[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
• Glossary of Terms:
  Term starting with letter: a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z
• References
• Members of IUPAC-IFCC/C-QU(CC) at the time of preparation
• Addresses of Authors

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 �.

Term	Symbol	Unit
absolute activity	[[lambda]]	1

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

�_B = 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, �_B.
2. The term component is recommended for clinical chemistry (2), ISO uses the term substance.
3. See relative activity.

Term	Symbol	Unit
absorbance	A	1

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(P_o/P_tr)
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.

Term	Symbol	Unit
absorbed dose	D	Gy

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

Term	Symbol	Unit
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.

Term	Symbol	Unit
absorption coefficient (linear)	a	m-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.

Term	Symbol	Unit
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.

Term	Symbol	Unit
acceleration	a	m s-2

Rate of change of velocity (10).

NOTE. a = dv/dt

Term	Symbol	Unit
acceleration of free fall	g	m s-2

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

NOTE. Also called acceleration due to gravity.

activity. See (relative) activity.

Term	Symbol	Unit
activity (of a radionuclide)	A	Bq

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).

Term	Symbol	Unit
activity coefficient	[[gamma]]	1

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

a_M,B = [[gamma]]_m,Bm_B/m- (T, p constant) (11)

when the solute substance (component), B, is in a solution containing molalities m_B, m_C,..., 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.

Term	Symbol	Unit
amount-of-substance	n	mol

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 Syst�me International d'Unit�s.
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.

Term	Symbol
ampere	A

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).

Term	Symbol	Unit
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

Term	Symbol
�ngstr�m	A

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).

Term	Symbol	Unit
area	A	m-2

A = || dx dy(12).

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

Term	Symbol
atmosphere, standard	atm

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

Term	Symbol	Unit
atomic mass	ma	kg

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.

Term	Symbol	Unit
atomic mass constant	mu	kg

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.

Term	Symbol	Unit
atomic number	Z	1

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

NOTE. Also known as proton number.

atomic weight. See relative atomic mass.

Term	Symbol	Unit
attenuance	D	1

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.

Term	Symbol	Unit
attenuation coefficient (linear)	m	m-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, �, by � = -(ln [[tau]])/l.
2. This quantity may also be called lineic attenuance.

Term	Symbol
atto	a

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

Term	Symbol	Unit
Avogadro constant	L, NA	mol-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

Term	Symbol
bar	bar

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).

Term	Symbol
becquerel	Bq

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

Term	Symbol	Unit
Boltzmann constant	k	J 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.

Term	Symbol
calorie	cal

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.

Term	Symbol
candela	cd

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).

Term	Symbol	Unit
capacitance	C	F

Electrical charge divided by potential difference (12).

Term	Symbol	Unit
catalytic activity	z	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.

Term	Symbol	Unit
catalytic activity concentration	b	kat 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.

Term	Symbol	Unit
catalytic activity content	z/m	kat/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.

Term	Unit
catalytic activity fraction	1

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.

Term	Symbol	Unit
Celsius temperature	t	�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.

Term	Symbol
centi	c

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

Term	Symbol	Unit
centripetal acceleration	arot	m s-2

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

Term	Symbol	Unit
centrifugal force	Frot	N

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

Term	Symbol	Unit
centrifugal radius	r	m

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.

Term	Symbol	Unit
charge number (of an ion)	z	1

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

chemical amount. See amount-of-substance.

Term	Symbol	Unit
chemical potential	�	J 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).

Term	Symbol	Unit
clearance	[[Delta]]V/[[Delta]]t	m3 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).

Term	Symbol
component	A, 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.

Term	Symbol	Unit
concentration gradient	grad C	m-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.

Term	Symbol	Unit
conductance	G	S

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

Term	Symbol	Unit
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).

Term	Symbol
coulomb	C

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

Term	Symbol
curie	Ci

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.

Term	Symbol
dalton	Da

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.

Term	Symbol
day	d

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).

Term	Symbol
deca	da

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

decay constant. See disintegration constant.

Term	Symbol
deci	d

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

Term	Symbol
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).

Term	Symbol
degree Celsius	�C

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

Term	Symbol	Unit
degree of dissociation	[[alpha]]	1

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

Term	Symbol	Unit
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.

Term	Symbol	Unit
diffusion coefficient	D	m2 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.

Term	Symbol	Unit
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.

Term	Symbol	Unit
distribution constant	KD	1

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).

Term	Symbol	Unit
distribution ratio	D	1

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 (D_c) when the amount of component is given as concentration.
5. Different units may be used for the stationary phase:
   i. gram dry phase (D_g - m³ g^-1).
   ii. cubic metre of bed volume (D_v - 1).
   iii. square metre of surface (D_s - m) .

dose. See absorbed dose and dose equivalent.

Term	Symbol	Unit
dose equivalent (effective of radiation)	H	Sv

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.

Term	Symbol	Unit
electric charge	Q	C

Integral of electric current over time (12).

NOTE. See electric current.

electric conductance. See conductance.

electric conductivity. See conductivity.

Term	Symbol	Unit
electric current	I	A

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

NOTE. See Syst�me International d'Unit�s.

Term	Symbol	Unit
electric current density	J	A 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.

Term	Symbol	Unit
electric field strength	E	V m-1

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

electric mobility. See mobility.

Term	Symbol	Unit
electric potential difference (of a galvanic cell)	[[Delta]]V	V

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.

Term	Symbol	Unit
electrode potential	E	V

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).

Term	Symbol	Unit
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.

Term	Symbol	Unit
electromotive force	E	V

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

Term	Symbol
electronvolt	eV

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.

Term	Symbol	Unit
elementary charge	e	C

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).

Term	Symbol	Unit
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.

Term	Symbol	Unit
enthalpy	H	J

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).

Term	Symbol	Unit
entropy	S	J 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.

Term	Symbol	Unit
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:
   i. molality, K_m [(mol kg^-1)]^{[[Sigma]][[upsilon]]}, when instead of concentrations molalities are used.
   ii. pressure, K_p [Pa^{[[Sigma]][[upsilon]]}], when components are gases and concentrations are expressed in terms of pressure.

Term	Symbol
erg	erg

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.

Term	Symbol
exa	E

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

Term	Symbol	Unit
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]]n_B/[[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.

Term	Symbol
farad	F

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.

Term	Symbol	Unit
Faraday constant	F	C mol-1

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

Term	Symbol
femto	f

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

Term	Symbol	Unit (of X)
flux	JX	s-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.

Term	Symbol	Unit
force	F	N

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

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

Term	Unit
fraction	1

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).

Term	Symbol	Unit
frequency	J	Hz

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.

Term	Symbol	Unit
friction factor	�	1

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.

Term	Symbol	Unit
Gibbs energy	G	J

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).

Term	Symbol
giga	G

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

Term	Symbol
gram	g

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".

Term	Symbol
gray	Gy

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).

Term	Symbol	Unit
half life	T1/2	s

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.

Term	Symbol	Unit
heat capacity	C	J 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).

Term	Symbol
hecto	h

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

Term	Symbol
henry	H

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

Term	Symbol
hertz	Hz

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

Term	Symbol
hour	h

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).

Term	Symbol	Unit
illuminance	E	lx

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

Term	Symbol	Unit
impedance	Z	[[Omega]]

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

NOTE. See resistance.

Term	Symbol	Unit
internal energy	U	J

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.

Term	Symbol
international calorie	calIT

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 cal_IT.
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 Syst�me International d'Unit�s.

Term	Symbol
international unit	int. 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).

Term	Symbol	Unit
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: I_c = 1/2[[Sigma]]c_Bz_B²
2. Ionic strength may also be expressed in terms of molality (I_m = 1/2[[Sigma]]m_Bz_B², unit: mol kg^-1).

Term	Symbol	Unit
ionic transport number	t	1

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.

Term	Symbol	Unit
irradiance	E	W m-2

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

NOTE. See radiant exitance.

Term	Symbol
joule	J

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.

Term	Symbol
katal	kat

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).

Term	Symbol
kelvin	K

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).

Term	Symbol
kilo	k

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

Term	Symbol
kilogram	kg

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.

Term	Symbol	Unit
kinetic energy	Ek	J

Energy of a body due to motion (11).

NOTE. E = 1/2mv²

Term	Symbol	Unit
kinematic viscosity	[[Theta]]	m2 s-1

Quotient of the viscosity and the density (11).

Term	Symbol	Unit
length	l	m

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

NOTE. See Systeme International d'Unit�s.

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).

Term	Symbol
litre	l 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).

Term	Symbol
lumen	lm

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

Term	Symbol	Unit
luminous flux	d[[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).

Term	Symbol	Unit
luminous intensity	I	cd

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

NOTE. See Syst�me International d'Unit�s.

Term	Symbol
lux	lx

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

NOTE. 1 lx = 1 m^-2 cd sr

Term	Symbol	Unit
mass	m	kg

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

NOTES

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

Term	Symbol	Unit
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.

Term	Symbol	Unit
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).

Term	Symbol	Unit
mass density gradient	grad [[rho]]	kg m-4

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

Term	Symbol	Unit
mass flow rate	qm	kg s-1

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

Term	Symbol	Unit
mass fraction	w	1

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.

Term	Symbol	Unit
mass number	A	1

Number of nucleons in an atomic nucleus (12).

NOTE. Also called nucleon number.

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

Term	Symbol	Unit
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).

Term	Symbol
mega	M

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

Term	Symbol
metre	m

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).

Term	Symbol	Unit
Michaelis constant	Km	mol 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.

Term	Symbol
micro	�

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

Term	Symbol
milli	m

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

Term	Symbol
millimetre of mercury	mmHg

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.

Term	Symbol
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).

Term	Symbol
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).

Term	Symbol	Unit
mobility (electric)	�	m2 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.

Term	Symbol	Unit
molality	m	mol 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.

Term	Symbol	Unit
molar conductivity	[[Lambda]] S	m2 mol-1

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

NOTES

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

Term	Symbol	Unit
(molar) gas constant	R	J 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

Term	Symbol	Unit
molar heat capacity	Cm	J mol-1 K-1

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

NOTE. See heat capacity.

Term	Symbol	Unit
molar mass	M	kg 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.

Term	Symbol	Unit
molar volume	Vm	m3 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.

Term	Symbol
mole	mol

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.

Term	Symbol	Unit
moment of inertia	I	m2 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).

Term	Symbol
nano	n

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

Term	Symbol
newton	N

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.

Term	Symbol	Unit
number concentration	CN	m-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.

Term	Symbol	Unit
number content	NB/m	kg-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.

Term	Symbol	Unit
number fraction	x	1

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.

Term	Symbol	Unit
number flow rate	qN	s-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.

Term	Symbol	Unit
number of entities	N	1

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).

Term	Symbol
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.

Term	Symbol	Unit
osmolality	m	mol 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.

Term	Symbol	Unit
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).

Term	Symbol	Unit
osmotic concentration	c	mol 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).

Term	Symbol	Unit
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).

Term	Symbol	Unit
partial mass density	[[rho]]B	kg 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.

Term	Symbol	Unit
partial pressure	pB	Pa

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

Term	Symbol	Unit
partial specific volume	vB	m3 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.

Term	Symbol
pascal	Pa

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

Term	Symbol	Unit
period	T	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.

Term	Symbol
peta	P

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).

Term	Symbol
pico	p

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

Term	Symbol	Unit
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.

Term	Symbol
poise	P

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.

Term	Symbol	Unit
power	P	W

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.

Term	Symbol	Unit
pressure	p	Pa

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).

Term	Symbol
rad	rad

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.

Term	Symbol
radian	rad

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.

Term	Symbol	Unit
radiant energy	Q	J

Energy propagated as electromagnetic radiation (5).

Term	Symbol	Unit
radiant exitance	M	W 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.

Term	Symbol	Unit
radiant power	P	W

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).

Term	Symbol	Unit
rate	x	s-1

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

NOTE. Rate of x is dx/dt.

Term	Symbol	Unit
rate coefficient	k	s-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.

Term	Symbol	Unit
rate constant	k	varies

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

Term	Symbol	Unit
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.

Term	Symbol	Unit
rate of reaction	v	mol m-3 s-1

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

NOTE. See extent of reaction.

Term	Unit
ratio	1

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

Term	Symbol	Unit
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.

Term	Symbol	Unit
refractive index	n	1

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.

Term	Symbol	Unit
(relative) activity	a	1

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

�_B = chemical potential of the component

�_B- = 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,�_B.
2. The term component is recommended for clinical chemistry (2), ISO uses the term substance.
3. See relative activity.

Term	Symbol	Unit
relative atomic mass	Ar	1

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.

Term	Symbol	Unit
relative density	d	1

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.

Term	Symbol	Unit
relative molecular mass	Mr	1

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.

Term	Symbol
rem	rem

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

Term	Symbol	Unit
resistance	R	[[Omega]]

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

Term	Symbol	Unit
resistivity	[[rho]]	[[Omega]] m

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

Term	Symbol
revolutions per minute	rpm

Non SI unit for rotational frequency (10).

NOTE. See rotational frequency.

Term	Symbol
r�ntgen	R

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.

Term	Symbol	Unit
rotational frequency	frot	Hz

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.

Term	Symbol	Unit
saturation fraction	sB	1

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.

Term	Symbol
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.

Term	Symbol
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).

Term	Symbol	Unit
sedimentation coefficient	sB	s

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.

Term	Symbol	Unit
sedimentation velocity	vB	m 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.

Term	Symbol
siemens	S

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.

Term	Symbol
sievert	Sv

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.

Term	Symbol
solid angle	sr

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.

Term	Symbol	Unit
specific activity	a	Bq 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.

Term	Symbol	Unit
specific heat capacity	c	J kg-1 K-1

Heat capacity divided by mass (12).

NOTE. See heat capacity.

Term	Symbol	Unit
specific volume	v	m3 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.

Term	Symbol
steradian	sr

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.

Term	Symbol
stokes	St

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).

Term	Symbol	Unit
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.

Term	Symbol	Unit
substance concentration	c	mol 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.

Term	Symbol	Unit
substance content	n/m	mol 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.

Term	Symbol	Unit
substance fraction	x	1

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.

Term	Unit
substance flow rate	mol 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.

Term	Symbol	Unit
surface density	[[rho]]S	kg m-2

Mass divided by area (12).

NOTE. The systematic name is areic mass.

Term	Symbol	Unit
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. Syst�me International d'Unit�s.

Syst�me International d'Unit�s (SI). Coherent system of units adopted and recommended by the Conf�rence G�n�ral de Poids et Mesures (CGPM) (14).

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

temperature. See thermodynamic temperature.

Term	Symbol
tera	T

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

Term	Symbol
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.

Term	Symbol	Unit
thermodynamic temperature	T	K

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

NOTE. See Syst�me International d'Unit�s.

Term	Symbol	Unit
time	t	s

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

NOTE. See Syst�me International d'Unit�s.

Term	Symbol
torr	torr

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.

Term	Symbol	Unit
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.

Term	Symbol	Unit
unified atomic mass unit	u	kg

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).

Term	Symbol	Unit
velocity	v	m s-1

Distance travelled divided by time of travel (10).

Term	Symbol	Unit
viscosity; dynamic viscosity	[[eta]]	Pa s

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

NOTE. [[tau]]_x,z = [[eta]](dv_x/dz)

Term	Symbol
volt	V

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.

Term	Symbol	Unit
volume	V	m3

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

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

Term	Symbol	Unit
volume flow rate	qv	m3 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.

Term	Symbol	Unit
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).

Term	Symbol	Unit
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).

Term	Symbol
watt	W

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.

Term	Symbol	Unit
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).

Term	Unit
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.

Term	Symbol
weber	Wb

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.

Term	Symbol	Unit
weight	G	N

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.

Term	Symbol	Unit
work	W	J

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

NOTE. See also joule.

Term	Symbol
yocto	y

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

Term	Symbol
yotta	Y

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

Term	Symbol
zepto	z

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

zeta potential. See electrokinetic potential.

Term	Symbol
zetta	Z

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

References

1. Dybkaer, R. and J�rgensen, 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: S�vres (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. F�rard (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 Bioqu�mica Cl�nica, Ciutat Sanit�ria i Universit�ria de Bellvitge, Feixa Llarga s/n, 08907 L'Hospitalet de Llobregat, Barcelona, Spain.

Louis F. Bertello, Prof., Per� 420, 1641 Acassuso, R. Argentina.

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