[IFCC-IUPAC/C-NPU documents | Contents]

GLOSSARY OF TERMS IN QUANTITIES AND UNITS IN CLINICAL CHEMISTRY

Prepared by The IUPAC-IFCC/C-NPU (formerly C-QU (CC)):

H. P. Lehmann, X. Fuentes-Arderiu, L. F. Bertello

Hypertext version January 1996 by Inge Ibsen

The following text is based on the document published in Biochim Clin 1995; 19: 471-502.

Contents

Introduction

The goals of the IUPAC Commission on Quantities and Units in Clinical Chemistry (IUPAC-CQUCC)/IFCC Committee on Quantities and Units (IFCC-CQU) (formerly Expert Panel on Quantities and Units - EPQU) are to participate in the definition and of quantities and units used for health care and related activities, and to ensure that such quantities and units are consistent with standards promulgated by authoritative international standards organizations in metrology. To achieve these goals, a number of documents prepared by the Commission/ Committee, with input from many clinical laboratory scientists worldwide, have been published since 1967 (1 - 10). A compendium of all these publications is currently in preparation.
Because of the importance of a consistent terminology in clinical chemistry and because these documents are often published in journals that may not be readily accessible, the Commission/Committee felt that a glossary containing those terms considered of particular use to the practising clinical chemist would be helpful to the clinical chemistry and clinical laboratory science communities. As a result, the glossary has been compiled from definitions taken from published documents of the Commission/Committee (1-10). Also it contains a number of terms, and their definitions, considered relevant to the practice of clinical chemistry, taken from the official documents of other commissions of IUPAC (11, 15, 17, 18) and of international scientific organizations such as the International Organization for Standardization (ISO) (12, 14), the International Bureau of Weights and Measures (Bureau International des Poids et Mesures-BIPM) (13, 14) and the International Union of Biochemistry and Molecular Biology (IUBMB) ((16, (19).

Glossary of terms

For the sake of uniformity some definitions have been slightly modified from the original source. The entries are given in the form: Term, Symbol and Unit (for quantities).

The use of "round" parentheses () around words of some terms means that these words may be omitted if it is unlikely that this will cause confusion.
The use of "double square brackets" is a result of describing Greek letters in HTML, f.ex.[[lambda]](Greek letter "lambda" in italic (sloping)); [[Delta]] (Greek capital letter "Delta" in upright (no sloping)). An exception is the Greek letter µ.

TermSymbolUnit
absolute activity[[lambda]] 1

Number defined by [[lambda]]B = exp(µB/RT) when a component, B, is in a mixture of components (11), where:

µB = chemical potential of the component

R = molar gas constant

T = thermodynamic temperature

NOTES

  1. The definition applies to specific entities (B) which should be specified as subscripts, i.e. [[lambda]]B, µB.
  2. The term component is recommended for clinical chemistry (2), ISO uses the term substance.
  3. See relative activity.

TermSymbolUnit
absorbanceA1

Negative logarithm of one minus absorptance as measured on a uniform sample (5).

NOTES

  1. A = -lg(1 - [[alpha]]) = -lg [[tau]] = lg(1/[[tau]]) = lg(Po/Ptr)
  2. Known as decadic absorbance. May be defined analogously as Napierian absorbance: B = -ln(1 - [[alpha]])
  3. The quantity is of practical use if [[tau]] refers to an internal measurement.
  4. The terms "optical density" and "extinction" have been used for this quantity, but this usage is discouraged because they now have other meanings.

absorbance, lineic. See absorption coefficient.

TermSymbolUnit
absorbed doseDGy

Energy imparted to matter by ionizing radiation in a suitable small element of volume divided by the mass of that element of volume (15).

TermSymbolUnit
absorptance[[alpha]]1

Radiant power absorbed by a system divided by the incident radiant power (5).

NOTES

  1. Also known as absorption factor.
  2. The quantity is only of practical use when radiant power is lost solely by absorption by the sample, and there is no loss of radiant power due to scattering or reflection.

absorption. See absorbance and absorption coefficient.

TermSymbolUnit
absorption coefficient (linear)am-1

Absorbance divided by the pathlength of a parallel beam within a uniform sample (5).

NOTES

  1. When the absorbance is the decadic absorbance the quantity is called linear (decadic) absorption coefficient.
  2. When the absorbance is the Napierian absorbance the quantity is called linear (Napierian) absorption coefficient, symbol [[alpha]].
  3. The term only applies if the decrease in radiant power is due to absorption. If power is lost through other, undefined, processes, the quantity is linear (decadic/Napierian) attenuation coefficient.
  4. This quantity may also be called lineic absorbance.
  5. Use of the term absorbtance per unit length for this quantity is not recommended.

TermSymbolUnit
absorption coefficient (molar)[[epsilon]] m2 mol-1

Absorption coefficient (linear) due to a component divided by the amount-of-substance concentration of that component in moles (5).

NOTES

  1. The quantity is known more precisely as the molar linear decadic absorption coefficient.
  2. When the absorbance is the Napierian absorbance, the quantity is called molar linear Napierian absorption coefficient, symbol [[kappa]].
  3. The term molar (decadic/Napierian) absorbtivity is also used for this quantity.
  4. The term extinction coefficient was used when concentration is expressed as mass concentration. Use of this term is not deprecated by IUPAC.

absorption factor. See absorptance.

TermSymbolUnit
accelerationam s-2

Rate of change of velocity (10).

NOTE. a = dv/dt

TermSymbolUnit
acceleration of free fallgm s-2

Acceleration of free fall in vacuum due to gravity (10).

NOTE. Also called acceleration due to gravity.

activity. See (relative) activity.

TermSymbolUnit
activity (of a radionuclide)ABq

Number of nuclear decays occurring in a given quantity of material in a small time interval, divided by the duration of that time interval (15).

TermSymbolUnit
activity coefficient[[gamma]]1

Number defined in terms of the (relative) activity aB of the solute substance B in the solution by:

aM,B = [[gamma]]m,BmB/m- (T, p constant) (11)

when the solute substance (component), B, is in a solution containing molalities mB, mC,..., of solute substances B, C, ..., in a solvent substance A, and m- is the standard molality.

NOTES

  1. The name activity coefficient may be used for the quantity similarly defined but with substance concentration or mole fraction in place of molality.
  2. The term component is recommended for clinical chemistry (2), ISO uses substance.

amount concentration. See substance concentration.

amount fraction. See substance fraction.

TermSymbolUnit
amount-of-substancenmol

Number of entities divided by the Avogadro constant (11).

NOTES

  1. Amount-of-substance is one of the base quantities on which the International System of Units is based (12).
  2. See Système International d'Unités.
  3. The entities may be atoms, molecules, ions, formula units, etc.
  4. The term amount-of-sustance is recommended for clinical chemistry (2), IUPAC also uses chemical amount (11).

amount-of-substance concentration. See substance concentration.

amount-of-substance content. See substance content.

amount-of-substance fraction. See substance fraction.

TermSymbol
ampereA

Base unit of the SI for electric current, equal to that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in vacuum, would produce between those conductors a force equal to 2 · 10-7 newton per metre of length (13).

TermSymbolUnit
angle[[alpha]], [[beta]], [[gamma]], J, ....rad

Ratio of the arc cut out in a circle with its centre at that point to the radius of the circle (12).

NOTES

  1. 1 rad = 1 m m-1 = 1
  2. See also radian, degree, minute, second

TermSymbol
ångströmA

Non SI unit of length equal to 10-10m.

NOTE. The unit is recognized by the CIPM for temporary use with the SI until considered no longer necessary (13).

TermSymbolUnit
areaA m-2

A = || dx dy(12).

areic. Modifier used to denote divided by area (7).

TermSymbol
atmosphere, standardatm

Non SI unit for pressure, defined by: 1 atm = 101 325 Pa (13).

TermSymbolUnit
atomic massmakg

Mass of an atom of a stated nuclide in its nuclear and atomic ground state (11).

NOTE. Also called the rest mass of an atom.

TermSymbolUnit
atomic mass constantmukg

Constant equal to 1/12 of the rest mass of a neutral atom of the nuclide 12C in its nuclear and atomic glound state (11).

NOTE. The atomic mass constant is equal to one unified atomic mass unit (11).

atomic mass unit. See unified atomic mass unit.

TermSymbolUnit
atomic number Z1

Number of protons contained in an atomic nucleus (12).

NOTE. Also known as proton number.

atomic weight. See relative atomic mass.

TermSymbolUnit
attenuanceD1

Negative logarithm of transmittance of a parallel beam through a uniform sample (5).

NOTES

  1. D = -lg [[tau]], where [[tau]] is the transmitance. Known as decadic attenuance. May be defined analogously as Napierian attenuance by De= -ln [[tau]].
  2. Attenuance is non specific and may be caused by loss of transmittance of a sample by absorption or scattering.

TermSymbolUnit
attenuation coefficient (linear)mm-1

Attenuance, D, divided by the pathlength, l, of a parallel beam through a sample of uniform properties (5).

NOTES

  1. m = D/l = -(lg [[tau]])/l, where [[tau]] is the transmitance. Known as linear (decadic) attenuation coefficient. May be defined analogously as linear (Napierian) attenuation coefficient, µ, by µ = -(ln [[tau]])/l.
  2. This quantity may also be called lineic attenuance.

TermSymbol
attoa

Prefix used with SI units to denote 10-18 (13).

TermSymbolUnit
Avogadro constantL, NAmol-1

Number of entities in a system divided by the amount-of-substance of those entities (11).

NOTE. L = N/n = 6,022 136 7(36) · 1023 mol-1

TermSymbol
barbar

Non SI unit for pressure equal to 105 Pa (13).

NOTE. Approved by the CIPM for temporary use with SI units until considered no longer necessary (13).

base quantity. One of the quantities that, in a system of quantities, are conventionally accepted as functionally independent of one another (14).

base unit (of measurement). Unit of measurement of a base quantity in a given system of quantities (14).

NOTE. See unit (of measurement).

TermSymbol
becquerelBq

SI unit of (radio)activity, equal to one nuclear decay per second (13).

TermSymbolUnit
Boltzmann constantkJ K-1

Molar gas constant divided by the Avogadro constant (11).

NOTES

  1. k = 1,380 658 (12) 10-23 J K-1.
  2. Also called the molecular gas constant.

TermSymbol
caloriecal

Unit for energy (heat) whose use with the International System of Units is generally deprecated (13).

NOTES

  1. See international calorie and thermochemical calorie.
  2. The use of the unit calorie is also deprecated by ISO, IUPAC and IFCC.

TermSymbol
candelacd

Base unit of the SI for luminous intensity, equal to the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 · 1012 hertz and that has a radiant intensity in that direction of (1/683) watt per steradian (13).

TermSymbolUnit
capacitanceCF

Electrical charge divided by potential difference (12).

TermSymbolUnit
catalytic activityz kat

Increase in the rate of reaction of a specified chemical reaction that an enzyme produces in a specific assay system (16).

NOTE. See rate of reaction.

TermSymbolUnit
catalytic activity concentrationbkat m-3

Catalytic activity of the component divided by the volume of the system (2).

NOTES

  1. In clinical chemistry litre is recommended as unit for the volume (2).
  2. In clinical chemistry the component is usually an enzyme.
  3. The term catalytic concentration is accepted for use in clinical chemistry.
  4. Use of the term level as a synonym for concentration is deprecated.
  5. In describing a quantity, concentration must be clearly differentiated from content.

TermSymbolUnit
catalytic activity contentz/mkat/kg

Catalytic activity of the component divided by the mass of the system (2).

NOTES

  1. In clinical chemistry the component is usually an enzyme.
  2. The term catalytic content is accepted for use in clinical chemistry.
  3. Use of the term level as a synonym for concentration is deprecated.
  4. In describing a quantity, content must be clearly differentiated from concentration.

TermUnit
catalytic activity fraction1

Quotient of the catalytic activity of the isozyme and the catalytic activity of all the isozymes of the same enzyme in the system.

NOTES

  1. The term catalytic fraction is accepted for use in clinical chemistry.
  2. The definition is based on the definitions of catalytic activity and fraction.
  3. The definition also applies to other multiple forms of an enzyme that are not isoenzymes.

catalytic concentration. See catalytic activity concentration.

catalytic content. See catalytic activity content.

catalytic fraction. See catalytic activity fraction.

TermSymbolUnit
Celsius temperaturet°C

Difference in the thermodynamic temperature of a body and the thermodynamic temperature of the triple point of water, minus 0,01 K (12).

NOTES

  1. The thermodynamic temperature of the triple point of water is 273,16 K.
  2. The old name centigrade for the unit degree Celsius is deprecated.

TermSymbol
centic

Prefix used with SI units to denote 10-2 (13).

TermSymbolUnit
centripetal accelerationarotm s-2

Acceleration of a component as a result of a uniform rotational motion (10).

TermSymbolUnit
centrifugal forceFrotN

Fictisious force acting on a body as a result of centripetal acceleration (10).

TermSymbolUnit
centrifugal radiusrm

Distance from the axis of rotation at which the component is spinning at the end of centrifugation (10).

charge. See electric charge and elementary charge.

TermSymbolUnit
charge number (of an ion)z1

Ratio of the electric charge carried by an ion to the elementary charge (18).

chemical amount. See amount-of-substance.

TermSymbolUnit
chemical potentialµJ mol-1

Quotient of the differential change in the internal energy of a component in a system and the differential change in the amount-of-substance of the component, maintaining other extensive quantities constant (4).

TermSymbolUnit
clearance[[Delta]]V/[[Delta]]tm3 s-1

Product of the concentration of a component in the output system and the volume flow rate of that output system divided by the concentration of this component in the input system (2).

NOTES

  1. The term mean volume rate is recommended for this quantity (2).
  2. The unit litre per second is recommended for clinical chemistry (2).

coefficient. Proportionality constant, k, in a multiplicative relationship between two quantities, A and B, having different dimensions, (A = k · B) (12).

NOTE. When the quantities A and B have the same dimension the proportionality constant is called a factor.

coherent system of units (of measurement). System of units of measurement in which all of the derived units are coherent (14).

NOTE. See coherent unit (of measurement) and derived unit (of measurement).

coherent (derived) unit (of measurement). Derived unit of measurement that may be expressed as a product of powers of base units with the proportionality factor one (14).

TermSymbol
componentA, B,....N

Stated part of a system (2).

NOTES

  1. When the component is in the form of atoms, molecules or ions it is called a chemical component; ISO uses the term substance.
  2. Components may also be cells (e.g. lymphocytes), chemical components that are not clearly characterized e.g. heparins), etc (2).
  3. A process ocurring in a system may be conventionally regarded as a component of that system (e.g. coagulation in blood).

concentration. See substance concentration.

TermSymbolUnit
concentration gradientgrad Cm-4

Differential change in concentration of a component in a given direction in a small distance divided by the distance in that direction (10).

NOTES

  1. It is a vector quantity.
  2. May be expressed as amount-of-substance, mass, number, volume, concentration gradient.

TermSymbolUnit
conductanceGS

Reciprocal of the electrical resistance of a conductor (12). See resistance.

TermSymbolUnit
conductivity[[gamma]]S m-1

Reciprocal of the resistivity of a conductor (12). See resistivity.

content. See substance content.

conventional true value (of a quantity). Value attributed to a particular quantity and accepted, sometimes by convention, as having an uncertainty appropriate for a given purpose (14).

TermSymbol
coulombC

SI unit for electric charge, equal to the electric charge carried in one second by a constant current of one ampere (13).

TermSymbol
curieCi

Non SI unit for the activity of a radionuclide, corresponding to 3,7 · 1010 disintegrations per second (13).

NOTES

  1. 1 Ci = 3,7 · 1010 Bq.
  2. Approved by the CIPM for temporary use with the SI until considered no longer necessary.

current density. See electric current density.

cycles per second. See hertz.

TermSymbol
daltonDa

Non SI unit equal to one unified atomic mass unit (11).

NOTES

  1. The dalton, with symbol Da, is frequently used in biochemistry to express molecular mass, although the name and the symbol have not been approved by CIPM or ISO.
  2. See unified atomic mass unit.

TermSymbol
dayd

Non SI unit for time equal to 86 400 seconds (13).

NOTE. Because of its importance and wide use, the CIPM approved the use of the day with SI units (13).

TermSymbol
decada

Prefix used with SI units to denote 101 (13).

decay constant. See disintegration constant.

TermSymbol
decid

Prefix used with SI units to denote 10-1 (13).

TermSymbol
degree°

Non SI unit for plane angle, equal to [[pi]]/180 rad (13).

NOTE. Because of its importance and wide use, The CIPM approved use of the degree with SI units (13).

TermSymbol
degree Celsius°C

Special name used in place of kelvin to express Celsius temperature (13).

TermSymbolUnit
degree of dissociation[[alpha]]1

Ratio of the number of dissociated molecules of a substance to the total number of molecules (12).

TermSymbolUnit
density[[rho]]kg m-3

Mass of a substance or body divided by its volume (11).

NOTES

  1. The recommended systematic name is volumic mass (7).
  2. See mass density.

derived quantity. Quantity defined, in a system of quantities, as a function of base quantities of that system (14).

NOTE. See quantity and base quantity.

derived unit (of measurement). Unit of measurement of a derived quantity in a given system of quantities (14).

NOTES

  1. See unit (of measurement) and derived quantity.
  2. Derived units are expressed algebraically in terms of base units by means of the mathematical symbols of multiplication and division.

TermSymbolUnit
diffusion coefficientDm2 s-1

Absolute value of the product of the local number concentration of a component and the local average velocity of particles of that component divided by the number concentration gradient in the direction of movement (10).

dimension (of a quantity). Expression that represents a quantity of a system of quantities as the product of powers of factors that represent the base quantities of the system (14).

NOTE. See base quantity.

dimensionless quantity. See quantity of dimension one.

TermSymbolUnit
disintegration constant[[lambda]]s-1

Probability of disintegration in a small time interval divided by the duration of the time interval (12).

NOTES

  1. Also called decay constant.
  2. Used primarily for radionuclide decay.

TermSymbolUnit
distribution constantKD1

Quotient of the concentration of a component in a single definite form in an organic solvent phase, or in the chromatographyc stationary phase, and its concentration in the same form in the aqueous phase, or in the chromatographic mobile phase, at equilibrium (17).

NOTES

  1. For clinical chemistry the term component is recommended (2), ISO uses substance.
  2. Also called partition coefficient, but use of this term is not recommended for this quantity (17).

TermSymbolUnit
distribution ratioD1

Quotient of the amounts of a component in two phases (17).

NOTES

  1. For clinical chemistry the term component is recommended(2), ISO uses substance.
  2. The quantity is used most frequently in chromatography, regarding the stationary phase and the mobile phase (17).
  3. The amount of component is the measured amount regardless of its form (cf. distribution constant refers to a specific form of the component).
  4. The quantity may be expressed as concentrational distribution ratio (Dc) when the amount of component is given as concentration.
  5. Different units may be used for the stationary phase:
  6. i. gram dry phase (Dg - m3 g-1).
  7. ii. cubic metre of bed volume (Dv - 1).
  8. iii. square metre of surface (Ds - m) .

dose. See absorbed dose and dose equivalent.

TermSymbolUnit
dose equivalent (effective of radiation)HSv

Absorbed dose multiplied by a quality factor and the product of all other modifying factors, aimed at expressing on a common scale, for different types of radiations and distributions of absorbed dose, the biological effects associated with exposure (15).

NOTE. See also absorbed dose.

dynamic viscosity. See viscosity.

electric capacitance. See capacitance.

TermSymbolUnit
electric chargeQC

Integral of electric current over time (12).

NOTE. See electric current.

electric conductance. See conductance.

electric conductivity. See conductivity.

TermSymbolUnit
electric currentIA

Base quantity of the International System of Units (12).

NOTE. See Systéme International d'Unités.

TermSymbolUnit
electric current densityJA m-2

Electric current divided by area (12).

NOTES

  1. It is the current per area of an electrode.
  2. Systematic name is areic electric current.

TermSymbolUnit
electric field strengthEV m-1

Force exerted by an electric field on a point charge divided by the electric charge (12).

electric mobility. See mobility.

TermSymbolUnit
electric potential difference (of a galvanic cell)[[Delta]]VV

Difference in the potentials of electrodes on the right and left of a galvanic cell (11).

NOTE. When [[Delta]]V is positive, positive charge flows from left to right through the cell.

electric resistance. See resistance.

electric resistivity. See resistivity.

TermSymbolUnit
electrode potentialEV

Electromotive force of a cell in which the electrode on the left is a standard hydrogen electrode and the electrode on the right is the electrode in question (11).

TermSymbolUnit
electrokinetic potential[[zeta]]V

Electric potential difference between the fixed charges on the immobile support and the diffuse charge in the solution (9).

NOTE. Also called zeta potential.

TermSymbolUnit
electromotive forceEV

Energy supplied by a source divided by the electric charge transported through the source (12).

TermSymbol
electronvolteV

Kinetic energy acquired by an electron passing through a potential difference of one volt (13).

NOTES

  1. 1 eV = 1,602 177 33(49)·10-19 J (13).
  2. One electronvolt is the elementary charge multiplied by 1 V.
  3. Because of its importance and use in specialized fields, the CIPM approved use of the electronvolt with SI units (13).

electrophoretic mobility. See mobility.

TermSymbolUnit
elementary chargeeC

Electric charge of a proton (12).

NOTES

  1. The value of the elementary charge is apromimately equal to 1,602 177 33(49) · 10-19 C (11).
  2. This quantity is also used as an atomic unit of electric charge (11).

TermSymbolUnit
emittance[[epsilon]]1

Radiant exitance of a sample divided by the radiant exitance of a black body at the same temperature (5).

NOTES

  1. The term emittance is preferred to the more widely used term "emissivity", which has been designated other meanings.
  2. As with other radiation quantities, emittance varies with wavelength.

TermSymbolUnit
enthalpyHJ

Thermodynamic quantity qiven by the sum of the internal energy and the product of the pressure and volume of a system (12).

entitic. Modifier used to denote divided by number of entities (7).

TermSymbolUnit
entropySJ K-1

Quantity defined by dS = dQ/T when an amount of heat dQ is received by a system having a thermodynamic temperature T, provided that no irreversible change takes place in the system (12).

enzyme activity. See catalytic activity.

TermSymbolUnit
equilibrium constant (concentration)Kc(mol m-3)[[Sigma]][[upsilon]]

Product of the substance concentrations of the components of a specified reaction to the power of their stoichiometric numbers in the reaction equation (11).

NOTES

  1. See stoichiometric number.
  2. The equilibrium constant may be defined in terms of:
  3. i. molality, Km [(mol kg-1)][[Sigma]][[upsilon]], when instead of concentrations molalities are used.
  4. ii. pressure, Kp [Pa[[Sigma]][[upsilon]]], when components are gases and concentrations are expressed in terms of pressure.

TermSymbol
ergerg

Non SI unit for energy (13).

NOTES

  1. 1 erg = 10-7 J.
  2. The erg is a unit of the CGS unit system, and its use is discouraged.

TermSymbol
exaE

Prefix used with SI units to denote 1018 (13).

TermSymbolUnit
extent of reaction[[Delta]][[xi]]mol

Change in the amount-of-substance of a component divided by the stoichiometric coefficient of the component (11).

NOTES

  1. Extent of reaction [[Delta]][[xi]] = [[Delta]]nB/[[Theta]]B.
  2. For clinical chemistry the term component is recommended (2), ISO uses substance.

extinction. Sum of the effects of absorption, scattering, and luminescence (11).

NOTE. Use of the term extinction to denote absorbance is deprecated by IUPAC.

extinction coefficient. See absorption coefficient (linear).

NOTE. Use of the term extintion coefficient to denote absorption coefficient is deprecated by IUPAC.

factor. Proportionality quantity, k, in a multiplicative relation between two quantities, A and B, having the same dimension, A=k · B (12)

NOTE. When the quantities A and B have different dimensions the proportionality quantity is called a coefficient.

TermSymbol
faradF

SI unit for capacitance, equal to the capacitance of a capacitor between the plates of which there appears a potential difference of 1 V when it is charged by a quantity of electricity of 1 C (13).

NOTE. 1 F = m-2 kg-1 s4 A2.

TermSymbolUnit
Faraday constantFC mol-1

Product of the Avogadro constant and the charge of the proton (11).

TermSymbol
femtof

Prefix used with SI units to denote 10-15 (13).

TermSymbolUnit (of X)
fluxJXs-1 m-2

Rate of movement of a quantity X per area of surface normal to flow, or interface through which the movement is taking place (11).

NOTES

  1. Flux may be expressed by (dX/dt)A-1.
  2. Flux is sometimes used to express transfer or movement of a component within a system or across its boundary.
  3. Transfer may be expressed as a flow rate, for example areic mass rate, areic substance rate or areic volume rate (8).
  4. This definition may not be useful for transport phenomena in electrochemical systems.

TermSymbolUnit
forceFN

Vector quantity equal to the product of the mass of a body and its acceleration (10).

NOTE. F = m(dv/dt) = m a

TermUnit
fraction1

Quotient where the numerator quantity refers to a component while the denominator is a quantity of the same kind for the whole system (7).

NOTE. From the definition, a fraction has a value between zero (included) and one (included).

TermSymbolUnit
frequencyJHz

Number of regular events in a given time divided by that time (12).

NOTE. For electromagnetic radiation the frequency is related to photon energy by E = hJ, where is the Planck constant. Frequency is also related to the speed of light, c, and the wavelength, [[lambda]] by the expression J = c/[[lambda]] (11).

friction coefficient. See friction factor.

TermSymbolUnit
friction factorµ1

Quotient of frictional force and normal force, for a sliding body (12).

NOTE. Formerly called frictional coefficient or coefficient of friction.

gas constant. See molar gas constant.

TermSymbolUnit
Gibbs energyGJ

Thermodynamic quantity equal to the difference between the enthalpy of a system and the product of the thermodynamic temperature to the entropy of this system (12).

TermSymbol
gigaG

Prefix used with SI units to denote 109 (13).

TermSymbol
gramg

Base unit for mass in the CGS system of units (13).

NOTES

  1. The gram is equal to 10-3 kilogram, the SI base unit for mass.
  2. Names of decimal multiples and submultiples of the unit of mass within the SI are formed by attaching prefixes to the word "gram".

TermSymbol
grayGy

SI unit for absorbed dose of radiant energy, equal to one joule per kilogram (13).

NOTE. The gray is a special unit of the SI permitted by the GIPM for reasons of safeguarding human health (13).

TermSymbolUnit
half lifeT1/2s

Average time required for the exponential decay of one half of the atoms of a sample of a radionuclide (12).

NOTES

  1. The term is generally used to denote the time taken in a chemical reaction for the initial amount (mass, amount-of-substance, concentration, etc.) of the component (substance) to be halved.
  2. The term also denotes the time in which the concentration of a substance will be reduced by half, assuming a first order elimination process.

TermSymbolUnit
heat capacityCJ K-1

Quantity equal to dQ/dT, where dT is the increase in thermodynamic temperature as a result of the addition of an amount of heat dQ to a system (12).

TermSymbol
hectoh

Prefix used with SI units to denote 102 (13).

TermSymbol
henryH

Inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per second (13).

NOTES

  1. The henry is the SI unit for inductance (13).
  2. H = 1 m2 kg s-2 A-2

TermSymbol
hertzHz

SI unit for frequency, equal to one cycle per second (13).

TermSymbol
hourh

Non-SI unit for time, equal to 3 600 s (13).

NOTE. Because of its importance and wide use, the CIPM approved use of the hour with SI units (13).

TermSymbolUnit
illuminanceElx

Luminous flux incident on an element of a surface, divided by the area of that element (12).

TermSymbolUnit
impedanceZ[[Omega]]

Complex representation of potential difference divided by the complex representation of current (12).

NOTE. See resistance.

TermSymbolUnit
internal energyUJ

Quantity defined as the sum of the heat Q added to a system and the work W done on the system (11).

NOTE U = Q + W. When Q > 0 and W > 0 there is an increase in the internal energy of the system.

TermSymbol
international caloriecalIT

Non-SI unit for energy, equal to 4,186 8 J (13).

NOTES

  1. The international calorie is distinguished from the thermochemical calorie by use of the notation calIT.
  2. See calorie and thermochemical calorie.
  3. Use of the unit international calorie is deprecated by CIPM, ISO, IUPAC and IFCC.

International System of Units. See Système International d'Unités.

TermSymbol
international unitint. unit

Arbitrary unit for a measurement that is agreed upon by the World Health Organization (2).

NOTE. Frequently used to express the results of measurement of a biological activity of a component.

ionic concentration. See ionic strength (concentrational).

TermSymbolUnit
ionic strength (concentrational)Ic mol m-3

One half the product of the concentration of an ion and its charge to the power 2 (11).

NOTES

  1. The ionic strength of a solution containing several ions is the sum of the ionic strengths of the individual ions: Ic = 1/2[[Sigma]]cBzB2
  2. Ionic strength may also be expressed in terms of molality (Im = 1/2[[Sigma]]mBzB2, unit: mol kg-1).

TermSymbolUnit
ionic transport numbert1

Quotient of the current carried by an ionic component and the total current (12).

NOTE. For clinical chemistry the term component is recommended (2), ISO uses substance.

TermSymbolUnit
irradianceEW m-2

Radiant power received by an element of surface divided by the area of that element (5).

NOTE. See radiant exitance.

TermSymbol
jouleJ

SI unit for energy, equal to the work done when the point of application of a force of one newton is displaced through a distance of one metre in the direction of the force (13).

NOTE. 1 J = 1 N m = 1 m2 kg s-2.

TermSymbol
katalkat

Unit for catalytic activity coherent with the SI, equal to the catalytic activity that catalyzes a reaction rate of one mole per second in an assay system (16).

NOTES

  1. 1 kat = 1 mol s-1 (16).
  2. The katal is recommended for use in the specific context of enzymes and clinical chemistry (2).

TermSymbol
kelvinK

Base unit of the SI for thermodynamic temperature, equal to the fraction 1/273,16 of the thermodynamic temperature of the triple point of water (13).

TermSymbol
kilok

Prefix used with SI units to denote 103 (13).

TermSymbol
kilogramkg

Base unit of the SI for mass, equal to the mass of the international prototype of the kilogram (13).

NOTE. The names of the multiples and sub-multiples of the unit of mass are formed by adding the prefixes to the word gram.

kind-of-quantity. Abstract property common to several real quantities (2). See quantity.

TermSymbolUnit
kinetic energyEkJ

Energy of a body due to motion (11).

NOTE. E = 1/2mv2

TermSymbolUnit
kinematic viscosity[[Theta]]m2 s-1

Quotient of the viscosity and the density (11).

TermSymbolUnit
lengthlm

Base quantity of the international system of units (12).

NOTE. See Systeme International d'Unités.

life-time. See mean life.

linear absorption coefficient. See absorption coefficient (linear).

linear attenuation coefficient. See attenuation coefficient (linear).

lineic. Modifier used to denote divided by length (7).

lineic absorbance. See absorption coefficient (linear).

TermSymbol
litrel or L

Non SI unit for volume, equal to 10-3 m3 (13).

NOTES

  1. Because of its importance and wide use, the CIPM approved use of the litre with SI units.
  2. The litre is the recommended volume for reporting results of clinical laboratory measurements, e.g. concentrations (2).

TermSymbol
lumenlm

SI unit for luminous flux, equal to the luminous flux emitted in unit solid angle (steradian) by uniform point source having a luminous intensity of 1 candela (13).

NOTE. 1 lm = 1 cd sr

TermSymbolUnit
luminous fluxd[[phi]]lm

Quantity defined as I · d[[Omega]], where I is the luminous intensity in an element of solid angle d[[Omega]], of a source (12).

TermSymbolUnit
luminous intensityIcd

Base quantity of the International System of Units (12).

NOTE. See Système International d'Unités.

TermSymbol
luxlx

SI unit for illuminance, equal to one lumen per square metre (13).

NOTE. 1 lx = 1 m-2 cd sr

TermSymbolUnit
massmkg

Base quantity of the International System of Units (12).

NOTES

  1. See Système International d'Unités.
  2. For a body, mass is the proportionality constant for the relation between the force applied to the body and its acceleration (12).

TermSymbolUnit
mass concentration[[rho]]kg m-3

Mass of the component divided by the volume of the system (2).

NOTES

  1. In clinical chemistry litre is recommended as unit for the volume (2).
  2. For clinical chemistry the term component is recommended (2), ISO uses substance.
  3. For clinical chemistry the term system is recommended (2), ISO uses mixture.
  4. Use of the term level as a synonym for concentration is deprecated.

TermSymbolUnit
mass density[[rho]]kg m-3

Mass of a system divided by its volume (10).

NOTE. The name volumic mass is recommended for this quantity (7).

TermSymbolUnit
mass density gradientgrad [[rho]]kg m-4

Change in mass density in a small distance divided by that distance (10).

TermSymbolUnit
mass flow rateqmkg s-1

Mass of a mater crossing a surface divided by the time (12).

TermSymbolUnit
mass fractionw1

Quotient of the mass of a component and the mass of the system containing the component (12).

NOTES

  1. For clinical chemistry the term component is recommended (2), ISO uses substance.
  2. For clinical chemistry the term system is recommended (2), ISO uses mixture.

TermSymbolUnit
mass numberA1

Number of nucleons in an atomic nucleus (12).

NOTE. Also called nucleon number.

massic. Modifier used to denote divided by mass (7).

TermSymbolUnit
mean life[[tau]]s

Number of entities of a component in a system at equilibrium divided by the number of entities of the component being transformed per time (18).

NOTES

  1. See half life.
  2. For a reacting system with first order kinetics, the mean life of a component is the time taken for the concentration of the component to fall to 1/e of its initial value.
  3. This quantity is also called life-time.

mean volume rate. See clearance.

measurand. Particular quantity subject to measurement (14).

TermSymbol
megaM

Prefix used with SI units to denote 106 (13).

TermSymbol
metrem

Base unit of the SI for length, equal to the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second (13).

TermSymbolUnit
Michaelis constantKmmol m-3

Substance concentration of substrate at which the rate of reaction is equal to one half of the limiting rate (maximum rate) (19).

NOTES

  1. Also called the Michaelis concentration
  2. The Michaelis constant (Michaelis concentration) may be used only when Michaelis-Menten kinetics is obeyed.

TermSymbol
microµ

Prefix used with SI units to denote 10-6 (13).

TermSymbol
millim

Prefix used with SI units to denote 10-3 (13).

TermSymbol
millimetre of mercurymmHg

Non SI unit for pressure (13).

NOTES

  1. 1 mmHg » 133,322 Pa.
  2. This old unit is not recognized by CIPM or ISO, but it is used for blood pressure.

TermSymbol
minute (of arc) '

Non SI unit for plane angle, equal to ([[pi]]/10 800) rad (13).

NOTE. Because of its importance and wide use, the CIPM approved use of the minute of arc with SI units (13).

TermSymbol
minute (of time)min

Non SI unit for time, equal to 60 s (13).

NOTE. Because of its importance and wide use, the CIPM approved use of the minute of time with SI units (13).

TermSymbolUnit
mobility (electric)µm2 V-1 s-1

Average drift velocity imparted to a charged particle in a medium by the electric field divided by the field strength (11).

NOTE. Is often preceded by the term electrophoretic or electrolytic to indicate mobility in a specific system.

molal. See molality.

TermSymbolUnit
molalitymmol kg-1

Amount-of-substance of a solute substance (component) (in a solution) divided by the mass of the solvent (11).

NOTES

  1. The term component is recommended for clinical chemistry (2), ISO uses substance.
  2. Use of the term molal for this quantity is not recommended.

molar. Modifier used to denote divided by amount-of-substance (7).

NOTE. Use of the term molar to denote a unit of amount-of-substance concentration is discouraged.

molar absorptivity. See absorption coefficent (molar).

molar absorption coefficient. See absorption coefficent (molar).

molar concentration. See substance concentration.

TermSymbolUnit
molar conductivity[[Lambda]] Sm2 mol-1

Conductivity of an electrolyte divided by its substance concentration (11).

NOTES

  1. See conductivity and resistivity.
  2. See substance concentration.

TermSymbolUnit
(molar) gas constantRJ K-1 mol-1

Universal constant of proportionality in the ideal gas law (11).

NOTE. The gas constant is equal to the product of the Avogadro constant and the Boltzmann constant:

R = Lk = 8,314 510 (70) J K-1 mol-1

TermSymbolUnit
molar heat capacityCmJ mol-1 K-1

Heat capacity divided by amount-of-substance (12).

NOTE. See heat capacity.

TermSymbolUnit
molar massMkg mol-1

Mass of a component divided by its amount-of-substance (12).

NOTE. The term component is recommended for clinical chemistry (2), ISO uses substance.

TermSymbolUnit
molar volumeVmm3 mol-1

Volume of a component divided by its amount-of-substance (12).

NOTE. The term component is recommended for clinical chemistry (2). ISO uses substance.

molarity. See substance concentration.

NOTE. Use of the term molarity to describe the amount-of-substance concentration is not recommended.

TermSymbol
molemol

Base unit of the SI for amount-of-substance, equal to the amount-of-substance of a system which contains as many elementary entities as there are atoms in 0,012 kilogram of carbon 12 (13).

NOTE. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

mole fraction. See substance fraction.

molecular weight. See relative molecular mass.

TermSymbolUnit
moment of inertiaIm2 kg

Sum (or integral) of the products of the masses of the elements of a body rotating about an axis and the squares of their distances from the axis (10).

TermSymbol
nanon

Prefix used with SI units to denote 10-9 (13).

TermSymbol
newtonN

SI unit for force, equal to the force required to accelerate a body with the mass one kilogram by one metre per second per second (13).

NOTE. 1 N = m kg s-2.

TermSymbolUnit
number concentrationCNm-3

Number of defined particles, or elementary entities, of a component in a system divided by the volume of that system (2).

NOTES

  1. In clinical chemistry, the litre is recommended as a unit for the volume of system (2).
  2. The term component is recommended for clinical chemistry (2), ISO uses substance.
  3. The term system is recommended for clinical chemistry (2), ISO uses mixture.
  4. Use of the term level as a synonym for concentration is deprecated.
  5. In describing a quantity, concentration must be clearly distinguished from content.

TermSymbolUnit
number contentNB/mkg-1

Number of defined particles, or elementary entities, of a component in a system divided by the mass of that system (2).

NOTES

  1. The term component is recommended for clinical chemistry (2), ISO uses substance.
  2. The term system is recommended for clinical chemistry (2), ISO uses mixture.
  3. Use of the term level as a synonym for concentration is deprecated.
  4. In describing a quantity, content must be clearly distinguished from concentration.

TermSymbolUnit
number fractionx1

Number of defined particles, or elementary entities of a specified component divided by the total number of defined particles in the system (2).

NOTES

  1. The term component is recommended for clinical chemistry (2), ISO uses substance.
  2. The term system is recommended for clinical chemistry (2), ISO uses mixture.

TermSymbolUnit
number flow rateqNs-1

Number of defined particles, or elementary entities of a defined component, crossing a cross section divided by the time.

NOTES

  1. Here, number flow rate is defined by analogy, see mass flow rate and volume flow rate (12).
  2. The term component is recommended for clinical chemistry (2), ISO uses substance.

TermSymbolUnit
number of entitiesN1

Number of molecules or other elementary entities in a system (12).

numerical value (of a quantity). Quotient of the value of a quantity and the unit used in its expression (14).

NOTE. See value (of a quantity).

TermSymbol
ohm[[Omega]]

SI unit for electric resistance, equal to the electric resistance between two points of a conductor when a constant potential difference of 1 V, applied to these points, produces in the conductor a current of 1 A, the conductor not being the seat of any electromotive force (13).

NOTE. 1 [[Omega]] = V A-1 = m2 kg s-3 A-2

optical density. See absorbance.

NOTE. Use of the term optical density to denote absorbance is deprecated by IUPAC.

TermSymbolUnit
osmolalitymmol kg-1

Quotient of the negative natural logarithm of the rational activity of water and the molar mass of water (4).

osmolarity. See osmotic concentration.

TermSymbolUnit
osmotic coefficient[[phi]] 1

Quotient of the osmolality of a solute (component) and the sum of the molalities of all the solutes in the solution (4).

TermSymbolUnit
osmotic concentrationcmol m-3

Product of the osmolality and the mass density of water (4).

NOTES

  1. Formerly called osmolarity.
  2. The unit mole per litre is recommended for clinical chemistry (2).

TermSymbolUnit
osmotic pressure[[Pi]]Pa

Pressure difference between the solution and the pure solvent which provides the same chemical potential of the solvent in the solution and in the pure solvent (4).

NOTE. Also defined as the excess pressure required to maintain osmotic equilibrium between a solution and the pure solvent separated by a membrane permeable only to the solvent (12).

TermSymbolUnit
partial mass density[[rho]]Bkg m-3

Change in mass due to addition of a small amount of component to a system divided by the change in volume of the system (10).

NOTE. The systematic name is partial volumic mass.

TermSymbolUnit
partial pressurepBPa

Product of the amount-of-substance fraction of a gaseous component and the pressure of the gaseous system (12).

TermSymbolUnit
partial specific volumevBm3 kg-1

Change in volume of a system when a small amount of component is added divided by the mass of thae added component (10).

NOTE. The systematic name is partial massic volume.

partition coefficient. See distribution constant.

TermSymbol
pascalPa

SI unit for pressure, equal to of one newton acting perpendicular to a surface of area per square metre (13).

NOTE. 1 Pa = 1 N m-2 = 1 kg m-1 s-2

TermSymbolUnit
periodT s

A time divided by the number of regularly repeating events during that time (12).

NOTE. It is the time taken to complete one cycle of a defined event.

TermSymbol
petaP

Prefix used with SI units to denote 1015 (13).

pH. Quantity of dimension one used to express the hydrogen ion concentration of dilute aqueous solutions, where:

pH » -lg[[[gamma]]+/-c(H+)/mol L-1] +/- 0,02 (11).

NOTES

  1. c(H+) denotes the amount-of-substance concentration of hydrogen ion and [[gamma]]+/- denotes the mean ionic activity coefficient of a typical uni-univalent electrolyte in the solution on a concentration of substance basis.
  2. The definition applies when the substance concentation of the solution is less than 0,1 mol L-1, and 2 < pH < 12 (11).

TermSymbol
picop

Prefix used with SI units to denote 10-12 (13).

TermSymbolUnit
plane angle[[alpha]], [[beta]], [[gamma]], J, ....rad

Ratio of the arc cut out in a circle with its centre at that point to the radius of the circle (12).

NOTES

  1. 1 rad = 1 m m-1 = 1
  2. See also radian, degree, minute, second.

TermSymbol
poiseP

Non SI unit for viscosity, equal to 0,1 Pa·s (13).

NOTE. The poise is a unit of the CGS unit system, and its use is discouraged.

TermSymbolUnit
powerPW

Rate of energy transfer (11).

NOTES

  1. 1 W = 1 J s-1
  2. In an electric direct current, power is the product of current and potential difference, 1 W = 1 V A.

TermSymbolUnit
pressurepPa

Force divided by the area over which the force is acting (12).

quantity. Attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined quantitatively (14).

NOTES

  1. The term quantity may refer to a quantity in a general sense, for example length, mass, or to a particular quantity, for example length of a particular rod, mass of a specified object.
  2. The term kind-of-quantity refers to the abstract concept of a quantity common to a group of related quantities (2).

quantity of dimension one; dimensionless quantity. Quantity in the dimensional expression of which all the exponents of the dimensions of the base quantities are zero (14).

TermSymbol
radrad

Non SI unit for absorbed dose of ionizing radiation, equal to one centigray (13).

NOTE. Approved by the CIPM for temporary use with the SI until considered no longer necessary.

TermSymbol
radianrad

SI unit for plane angle, equal to the angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius (13).

NOTES

  1. 1 rad = 57,29578°.
  2. The plane angle is a quantity of dimension one.

TermSymbolUnit
radiant energyQJ

Energy propagated as electromagnetic radiation (5).

TermSymbolUnit
radiant exitanceMW m-2

Radiant power emitted by an element of surface at uniform temperature divided by the surface area of that element (5).

radiant flux. See radiant power.

TermSymbolUnit
radiant powerPW

Amount of radiant energy transferred to or from a defined system divided by the time interval (5).

NOTE. Also called radiant (energy) flux.

radioactivity. See activity (radionuclide).

TermSymbolUnit
ratexs-1

Derived quantity in which time is a denominator quantity (7).

NOTE. Rate of x is dx/dt.

TermSymbolUnit
rate coefficientks-1

Number fraction of particles of a component in a medium passing a given position in the direction of an applied force divided by time (10).

NOTE. The applied force may be gravitational acceleration in column chromatography, rotational acceleration in centrifugation, electromotive force in electrophoresis.

TermSymbolUnit
rate constantkvaries

Proportionality coefficient in a chemical reaction rate equation (11).

TermSymbolUnit
rate of conversion[[xi]]mol s-1

Change in the extent of a reaction over a time interval divided by that time interval (11).

NOTE. See extent of reaction.

TermSymbolUnit
rate of reactionvmol m-3 s-1

Rate of conversion of a (given) reaction divided by the volume of the system (11).

NOTE. See extent of reaction.

TermUnit
ratio1

Quotient of quantities of the same kind for different components within the same system (7).

TermSymbolUnit
reflectance[[rho]]1

Radiant power specularly reflected from the surfaces of a system divided by the incident radiant power (5).

NOTES

  1. The quantity is also known as "specular reflectance" or "reflection factor".
  2. In the absence of scattering and luminescence, the sum of the transmittance, absorptance and reflectance at given spectral position is equal to one.

TermSymbolUnit
refractive indexn1

Quotient of the speed in vacuum of electromagnetic radiation at a given spectral position and its speed in a given medium (5).

NOTE. The medium must be non absorbing, i.e. not absorb the electromagnetic radiation at the spectral position.

relative. Quotient of quantities having the same kind-of-quantity in different systems (7).

NOTES

  1. The denominator quantity is often called the reference quantity.
  2. Preferentially the same component is found in the numerator and denominator quantity.

TermSymbolUnit
(relative) activitya1

Number defined by aB = exp(µB-µB-/RT) when a component, B, is in a mixture of components (11), where:

µB = chemical potential of the component

µB- = standard chemical potential of the component

R = molar gas constant

T = thermodynamic temperature

NOTES

  1. The definition applies to specific entities (B) which should be specified as subscripts, i.e. [[lambda]]B,µB.
  2. The term component is recommended for clinical chemistry (2), ISO uses the term substance.
  3. See relative activity.

TermSymbolUnit
relative atomic massAr1

Ratio of the average mass per atom of an element to 1/12 of the mass of an atom of nuclide 12C (12).

NOTE. Also known as atomic weight.

TermSymbolUnit
relative densityd1

Quotient of the density of a substance and the density of a reference substance under specified conditions (12).

NOTES

  1. The systematic name is relative volumic mass.
  2. The term specific gravity is not recommended.

TermSymbolUnit
relative molecular massMr1

Ratio of the average mass per molecule of a compound to 1/12 of the mass of an atom of nuclide 12C (12).

NOTE. Also known as molecular weight.

TermSymbol
remrem

Non SI unit for dose equivalent, equal to one centisievert (13).

NOTES

  1. Approved by the CIPM for temporary use with SI units until considered no longer necessary.
  2. It is a special unit used to express dose equivalent in radioprotection.

repetency. wavenumber.

See
TermSymbolUnit
resistanceR[[Omega]]

Electric potential difference divided by the electric current when there is no electromotive force in a conductor (12).

TermSymbolUnit
resistivity[[rho]] [[Omega]] m

Electric field strength divided by the current density when there is no electromotive force in a conductor (12).

TermSymbol
revolutions per minuterpm

Non SI unit for rotational frequency (10).

NOTE. See rotational frequency.

TermSymbol
röntgenR

Non SI unit used to express exposure to ionizing radiation (13).

NOTES

  1. Approved by the CIPM for continued use with SI units until considered no longer necessary.
  2. 1 R = 2,58 · 10-4 C kg-1.

TermSymbolUnit
rotational frequencyfrotHz

Number of rotations divided by time (10).

NOTES

  1. The not recommended units revolutions per minute (rpm) and revolutions per second (rps) are usually used in specifications for rotationary equipment, for example centrifuges.
  2. Not recommended synonyms are rate of rotation, rate of revolution, centrifugal speed, centrifugation speed.

TermSymbolUnit
saturation fractionsB1

Amount-of-substance of a component (solute) in a solution divided by the amount-of-substance of the component when it is saturating the system at constant temperature and pressure (4).

NOTE. Also referred to simply as saturation, for example oxygen saturation.

TermSymbol
second (of arc) "

Non SI unit for plane angle, equal to ([[pi]]/648 000) rad (13).

NOTE. Because of its importance and wide use, the CIPM approved use of the second (of arc) with SI units.

TermSymbol
second (of time)s

Base unit of the SI for time, equal to the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom (13).

TermSymbolUnit
sedimentation coefficientsBs

Reciprocal of the rate coefficient of a suspended component in a fluid passing a given position in the direction of gravitational or centrifugal acceleration (10).

NOTES

  1. For clinical chemistry the term component is recommended (2), ISO uses substance.
  2. Use of the Svedberg unit for this quantity is not recommended.

TermSymbolUnit
sedimentation velocityvBm s-1

Velocity of a component in a fluid relative to the fluid in the direction of gravitational or centrifugal acceleration (10).

NOTES

  1. Also called sedimentation rate.
  2. For clinical chemistry the term component is recommended (2), ISO uses substance.

TermSymbol
siemensS

SI unit for electric conductance, equal to the conductance between two points of a conductor having a resistance of 1 [[Omega]] (13).

NOTE. 1 S = 1 A V-1 = 1 m-2 kg-1 s3 A2.

TermSymbol
sievertSv

SI unit for dose equivalent of absorbed radiant energy (13).

NOTES

  1. The sievert is a special derived unit of the SI permitted by the CIPM for reasons of safeguarding human health.
  2. 1 Sv = 1 J kg-1 = 1 m2 s-2.

TermSymbol
solid anglesr

Ratio of the area cut out on a spherical surface (with its centre at the apex of a cone) to the square of the radius of the sphere (12).

NOTE. See also steradian.

specific. Modifier used to denote divided by mass (12).

EXAMPLES. specific activity, specific heat.

NOTE. Use of the term massic instead of specific is recommended (7), for example, massic activity, massic heat, etc.

TermSymbolUnit
specific activityaBq kg-1

Activity of a sample divided by its mass (12).

NOTES

  1. The ISO definition is given for radionuclides with a unit Bq kg-1.
  2. For radionuclides, the systematic name is massic radioactivity.

specific conductance. See conductivity.

TermSymbolUnit
specific heat capacitycJ kg-1 K-1

Heat capacity divided by mass (12).

NOTE. See heat capacity.

TermSymbolUnit
specific volumevm3 kg-1

Volume of a substance divided by its mass (12).

NOTES

  1. It is the reciprocal of mass density.
  2. A synonym is massic volume (7).

speed. See velocity.

standard atmosphere. See atmosphere.

TermSymbol
steradiansr

SI unit for solid angle, equal to the solid angle extending from the centre of a sphere to span an area on its surface equal to the square of the radius (13).

NOTE. The solid angle is a quantity of dimension one.

TermSymbol
stokesSt

Unit for kinematic viscosity in the CGS system of units (13).

NOTES

  1. 1 St = 1 cm2 s-1 = 10-4 m2 s-1.
  2. Use of the Stokes is not recommended with the SI (13).

TermSymbolUnit
stoichiometric number[[nu]]1

Number or simple fraction for a substance (component) occurring in the expression for a chemical reaction (12).

NOTES

  1. The stoichiometric number is negative for reactants and positive for products in the reaction equation (11).
  2. For clinical chemistry the term component is recommended (2), ISO uses substance.

TermSymbolUnit
substance concentrationcmol m-3

Amount-of-substance of a component divided by the volume of the system (2).

NOTES

  1. The term substance concentration is recommended for clinical chemistry (2), IUPAC also uses amount concentration (11), and ISO uses concentration.
  2. The term component is recommended for clinical chemistry (2), ISO uses substance.
  3. The term system is recommended for clinical chemistry (2), ISO uses mixture.
  4. The unit mole per litre is recommended for clinical chemistry (2).
  5. Use of the term molarity for this quantity is not recommended.
  6. Use of the term level as a synonym for concentration is deprecated.
  7. In describing a quantity, concentration must be clearly differentiated from content.

TermSymbolUnit
substance contentn/mmol kg-1

Amount-of-substance of a component divided by the mass of the system (2).

NOTES

  1. The term component is recommended for clinical chemistry (2), ISO uses substance.
  2. The term system is recommended for clinical chemistry (2), ISO uses mixture.
  3. Use of the term level as a synonym for content is deprecated.
  4. In describing a quantity, content must be clearly differentiated from concentration.

TermSymbolUnit
substance fractionx1

Ratio of the amount-of-substance of the component to the total amount-of-substance in the system containing the component (2).

NOTES

  1. The term substance fraction is recommended for clinical chemistry (2), IUPAC also uses mole fraction and amount fraction (11).
  2. For clinical chemistry the term component is recommended (2), ISO uses substance.
  3. For clinical chemistry the term system is recommended (2), ISO uses mixture.

TermUnit
substance flow ratemol s-1

Amount-of-substance of a component crossing a surface divided by the time (12).

NOTE. For clinical chemistry the term component is recommended (2). ISO uses substance.

TermSymbolUnit
surface density[[rho]]Skg m-2

Mass divided by area (12).

NOTE. The systematic name is areic mass.

TermSymbolUnit
surface tension[[gamma]]N m-1

Force perpendicular to a line element in a surface divided by the length of the line element (12).

symbol (in quantities and units). Conventional sign designating a quantity or a unit of measurement (12).

NOTES

  1. Symbols for quantities are denoted by letters of the Latin or Greek alphabet printed in italic (sloping) type; pH is an exception.
  2. Symbols for units are denoted by letters of the Latin or Greek alphabet printed in roman (upright) type.

system. Arbitrarily defined part of the universe, regardless of form or size (1).

EXAMPLES. patient, patient plasma, patient urine.

system of units (of measurement). Set of base units, together with derived units, defined in accordance with given rules, for a given system of quantities (14).

EXAMPLE. Système International d'Unités.

Système International d'Unités (SI). Coherent system of units adopted and recommended by the Conférence Général de Poids et Mesures (CGPM) (14).

NOTE. At present, the SI is based on the following seven base units (13):

  • the metre, unit of length
  • the kilogram, unit of mass
  • the second, unit of time
  • the ampere, unit of electric current
  • the kelvin, unit of thermodynamic temperature
  • the mole, unit of amount-of-substance
  • the candela, unit of luminous intensity
  • temperature. See thermodynamic temperature.

    TermSymbol
    teraT

    Prefix used with SI units to denote 1012 (13).

    TermSymbol
    thermochemical calorie calth

    Non SI unit for energy, equal to 4,184 J (13).

    NOTES

    1. The thermochemical calorie is distinguished from the international calorie by use of the notation calth.
    2. See calorie.
    3. Use of the unit thermochemical calorie is deprecated by CIPM, ISO, IUPAC and IFCC.

    TermSymbolUnit
    thermodynamic temperatureT K

    Base quantity of the International System of Units (12).

    NOTE. See Système International d'Unités.

    TermSymbolUnit
    timets

    Base quantity of the International System of Units (12).

    NOTE. See Système International d'Unités.

    TermSymbol
    torrtorr

    Non SI unit for pressure (11).

    NOTES

    1. 1 torr = 133,332 Pa.
    2. Use of the unit torr is generally deprecated (13).

    transmission. See transmittance.

    TermSymbolUnit
    transmittance[[tau]]1

    Radiant power transmitted by a system in the direction of a parallel beam, divided by the incident radiant power (5).

    NOTES

    1. The symbol T may be used instead of [[tau]].
    2. The term transmission is used for this quantity but is not recommended.

    true value (of a quantity). Value consistent with the definition of a given particular quantity (14).

    NOTES

    1. The true value of a quantity is an ideal concept and, in general, cannot be known exactly.
    2. It is a value that would be obtained by a perfect measurement.
    3. The best approximation to the true value is obtained using a definitive measurement procedure.
    4. See conventional true value.

    TermSymbolUnit
    unified atomic mass unitukg

    Non SI unit for mass, equal to 1/12 of the rest mass of a neutral atom of the nuclide 12C in its nuclear and atomic glound state (11).

    NOTES

    1. 1 u = 1,660 540 2(10) · 10-27 kg (13).
    2. Because of its importance ans use in specialized fields, the CIPM approved use of the unified atomic mass unit with SI units (13).
    3. The unified atomic mass unit is also sometimes called the dalton, with symbol Da, althought the name and the symbol have not been approved by CIPM or ISO.

    unit (of measurement). Particular quantity, defined and adopted by convention, with which other quantities of the same kind are compared in order to express their magnitudes relative to that quantity (14).

    value (of a quantity). Magnitude of a particular quantity generally expressed as a unit of measurement multiplied by a number (14).

    TermSymbolUnit
    velocityvm s-1

    Distance travelled divided by time of travel (10).

    TermSymbolUnit
    viscosity; dynamic viscosity[[eta]]Pa s

    Constant of proportionality for shear stress, [[tau]]xz, in a fluid moving with a velocity gradient dvx/dz perpendicular to the plane of shear (10).

    NOTE. [[tau]]x,z = [[eta]](dvx/dz)

    TermSymbol
    voltV

    SI unit for electric potential, equal to the potential difference between two points of a conducting wire carrying a constant current of 1 A, when the power dissipated between these points is equal to 1 W (13).

    NOTE. 1 V = 1 W A-1 = 1 m2 kg s-3 A-1.

    TermSymbolUnit
    volumeVm3

    V = ||| dx dy dz (12).

    NOTE. In clinical chemistry the litre, symbol l or L, is the recommended unit for volume (2).

    TermSymbolUnit
    volume flow rateqvm3 s-1

    Volume of a component crossing a surface divided by the time (12).

    NOTE. For clinical chemistry the term component is recommended (2), ISO uses substance.

    TermSymbolUnit
    volume fraction[[phi]] 1

    Quotient of the volume of a component and the total volume of the system containing the component (12).

    NOTES

    1. For clinical chemistry the term component is recommended (2), ISO uses substance.
    2. For clinical chemistry the term system is recommended (2), ISO uses mixture.

    volume rate. See clearance.

    volumic. Modifier used to denote divided by volume of the system (7).

    TermSymbolUnit
    volumic mass[[rho]]kg m-3

    The volumic mass of a substance is its mass divided by its volume (7).

    NOTES

    1. See density.
    2. For clinical chemistry the volume litre is recommended (2).

    TermSymbol
    wattW

    The watt is the SI unit for power, equal to the power which in 1 s give rise to energy of 1 J (13).

    NOTE. 1 W = 1 J s-1 = 1 m2 kg s-3.

    TermSymbolUnit
    wavelength[[lambda]]m

    Distance in the direction of propagation of a regular wave divided by the number of cycles of the wave in that distance (5).

    TermUnit
    wavenumber (in a vacuum)J m-1

    Number of cycles of a regular wave in a given distance divided by that distance (5).

    NOTE. The systematic name is repetency.

    TermSymbol
    weberWb

    The weber is the SI unit for magnetic flux, equal to the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 V if it were reduced to zero at a uniform rate of 1 s (13).

    NOTE. 1 Wb = 1 V s = 1 m2 kg s-2 A-1.

    TermSymbolUnit
    weightGN

    Force which when applied to a body in a specified reference system would give it an acceleration equal to the local acceleration of free fall in that reference system (12).

    NOTE. The term weight is often used as a synonym for mass, but this usage is discouraged.

    TermSymbolUnit
    workWJ

    Force multiplied by the displacement in the direction of the force (12).

    NOTE. See also joule.

    TermSymbol
    yoctoy

    Prefix used with the SI to denote 10-24 (13).

    TermSymbol
    yottaY

    Prefix used with the SI to denote 1024 (13).

    TermSymbol
    zeptoz

    Prefix used with the SI to denote 10-21 (13).

    zeta potential. See electrokinetic potential.

    TermSymbol
    zettaZ

    Prefix used with the SI to denote 1021 (13).


    References

    1. Dybkaer, R. and Jørgensen, K. Quantities and Units in Clinical Chemistry Including Recommendation 1966 of the Commission on Clinical Chemistry of the IUPAC and of the IFCC. x + 102 pp. Munksgaard: Copenhagen (1967).
    2. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Expert Panel on Quantities and Units. Quantities and Units in Clinical Chemistry, (Recommendations 1979). Pure & Appl. Chem., 1:2451-2479 (1979), and Clin. Chim. Acta 96:157F-183F (1979).
    3. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Expert Panel on Quantities and Units. List of Quantities in Clinical Chemistry, (Recommendations 1979). Pure & Appl. Chem., 51:2481-2502(1979) and Clin. Chim. Acta 96:185F-204F (1979).
    4. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Expert Panel on pH and Blood Gases. Physicochemical Quantities and Units in Clinical Chemistry with Special Emphasis on Activities and Activity Coefficients, (Recommendations 1983). Pure & Appl. Chem., 56:567-594 (1984), and J. Clin. Chem. Clin. Biochem., 25:369-391 (1987).
    5. International Union of Pure and Applied Chemistry Commission on Molecular Structure and Spectroscopy, and Commission on Quantities and Units in Clinical Chemistry. Names, Symbols, Definitions and Units of Quantities in Optical Spectroscopy, (Recommendations 1985). Pure & Appl. Chem., 57:105-120 (1985).
    6. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Expert Panel on Quantities and Units. Quantities and Units in Clinical Chemistry: Nebulizer and Flame Properties in Flame Emission and Absorption Spectrometry, (Recommendations 1986). Pure & Appl. Chem., 58:1737-1742 (1986) and J. Clin. Chem. Clin. Biochem., 23:365-371 (1985).
    7. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry. Nomenclature of Derived Quantities (Recommendations 1991). Pure & Appl. Chem., 63:1307-1311 (1991).
    8. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Committee on Quantities and Units. Quantities and Units for Metabolic Processes as a Function of Time (Recommendation 1992). Pure & Appl. Chem., 64:1569-1575 (1992), Eur. J. Clin. Chem. Clin. Biochem., 30:901-905 (1992) and Clin. Chim. Acta, 211:S5-S11 (1992).
    9. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Committee on Quantities and Units. Quantities and Units for Electrophoresis in the Clinical Laboratory (Recommendations 1994). Pure & Appl. Chem., 66:891-896 (1994) and Clin. Chim. Acta., 205:S17-S23 (1992).
    10. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry/International Federation of Clinical Chemistry Committee on Quantities and Units. Quantities and Units for Centrifugation in the Clinical Laboratory (Recommendations 1994). Pure & Appl. Chem., 66:897-907 (1994) and Ann. Biol. Chem., 50:45-49 (1992).
    11. International Union of Pure and Applied Chemistry Commission on Physicochemical Symbols Terminology and Units. Quantities, Units and Symbols in Physical Chemistry. 2nd Edition. Blackwell Scientific Publications: Oxford (1993).
    12. International Standards Organization. ISO Standards Handbook; Quantities and units. 3rd edition. International Standards Organization: Geneva (1993).
    13. Bureau International des Poids et Mesures. The International System of Units (SI). 6th Edition. Bureau International des Poids et Mesures: Sèvres (1991).
    14. International Bureau of Weights and Measures, International Electrotechnical Commission, International Organization for Standardization, International Organization of Legal Metrology, International Federation of Clinical Chemistry, International Union of Pure and Applied Chemistry and International Union of Pure and Applied Physics. International Vocabulary of Basic and General Terms in Metrology. 2nd Edition. International Organization for Standardization: Geneva (1993).
    15. International Union of Pure and Applied Chemistry Commission on Analytical Radiochemistry and Nuclear Materials. Glossary of Terms used in Nuclear Analytical Chemistry. Pure & Appl. Chem., 54:1533-1554 (1982).
    16. Nomenclature Committee of the International Union of Biochemistry. Units of Enzyme Activity, Recommendations 1978. Eur. J. Biochem., 97:319-320 (1979).
    17. International Union of Pure and Applied Chemistry Analytical Chemistry Division. Compendium of Analytical Nomenclature. Definitive Rules 1987. Blackwell Scientific Publications: Oxford (1987).
    18. International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology. IUPAC Recommendations. Blackwell Scientific Publications: Oxford (1987).
    19. Nomenclature Committee of the International Union of Biochemistry. Symbolism and Terminology in Enzyme Kinetics. Arch. Bioch. Bioph., 224:732-740 (1983).

    Membership of the Commission and the Committee for varying periods during which this glossary was prepared was as follows:

    Chairmen: H. P. Lehmann (USA); H. Olesen (Denmark),

    Titular Members: D. R. Bangham (UK); L. F. Bertello (Argentina); G. Férard (France); X. Fuentes-Arderiu (Spain); J. G. Hill (Canada); M. Lauritzen (Denmark); P. Storring (UK),

    Associate Members: S. J. Bryant (Australia); D. J. Cambell (Canada); J. Kratochvila (Czech Republic); C. Onkelinx (Belgium); O Siggaard-Andersen (Denmark); P. Soares de Araujo (Brazil); C-H. de Verdier (Sweden); B. F. Visser (Netherlands); U. Worsaae (Denmark); R. Zender (Switzerland).


    Addresses of Authors

    H. Peter Lehmann, Ph.D., Dept. of Patholgy, Louisiana State Univ. Med. Center, 1901 Perdido Street, New Orleans, Louisiana 70112, USA.

    X. Fuentes-Arderiu, Ph.D., Servei de Bioquímica Clínica, Ciutat Sanitària i Universitària de Bellvitge, Feixa Llarga s/n, 08907 L'Hospitalet de Llobregat, Barcelona, Spain.

    Louis F. Bertello, Prof., Perù 420, 1641 Acassuso, R. Argentina.


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