1、International Standard 6286 0 4ib INTERNATIONAL ORGANIZATION FOR STANOAAOlZATlONMEYHAPOHAR OPrAHH3AUblR fl0 CTAHWTbl3AUWORGANlSATiON INTERNATIONALE DE NORMALISATION Molecular absorption spectrometry - Vocabulary - General - Apparatus Spectromdtrie b) the characteristics and qualities of an instrumen
2、t, by giving a summary of the principles of certain methods of verifying them. 2 Terms, definitions, symbols, formulae and units Molecular absorption spectrometry is a technique applicable to both qualitative and quantitative analyses and it enables measurements to be made of the concentration of a
3、compound dissolved in a solution; it is effective in the near ultraviolet, visible and near infra-red regions, which correspond to a wavelength interval from about 186 to 1 000 nm. The terms given in tables 1 and 2 are classified so that they are defined before their use in later definitions. Table
4、1 is given for the purposes of comprehensiveness; it collates terms from the Vocabulaire international de Ieclairage (International lighting vocabulary), account of which has been taken in the choice of terms and in the drawing up of the defini- tions forming the subject of table 2. In table 1 - ter
5、ms 1 to 8 relate to the interaction of any electro- magnetic radiation of an optical nature (UV, visible, IR) with any medium observed from the outside; - terms 9 to 11 relate to the interaction of any electro- magnetic radiation of an optical nature (UV, visible, IR) with a medium with plane and pa
6、rallel surfaces, which is homogeneous, isotropic, non-luminescent and non- scattering, observed from the inside. Table 2 is in line with the scope of this International Standard and therefore concerns the interaction of a beam of monochromatic luminous radiation striking, at normal incidence, a medi
7、um consisting of a solution which is homogeneous, isotropic, non-luminescent and non-diffusing contained in an optical cell (with two plane and parallel sur- faces). In table 2 - terms 14 and 15 relate to the theoretical aspect, and are a simple adaptation of terms 9 and 11 to the special case of mo
8、lecular absorption spectrometry; - terms 16 to 20 relate to actual phenomenaand measure- ments; - terms 21 and 22 relate to the method of expression of results. A list of the French terms equivalent to those defined in tables 1 and 2 is given in the annex. 3 General Molecular absorption spectrometry
9、 obeys the following laws. 3.1 Lambert-Bouguers law When a parallel beam of monochromatic radiation of flux e traverses, at normal incidence, an absorbing medium with plane, parallel surfaces and which is homogeneous, isotropic, non-luminescent and non-scattering, over an optical path length 6, the
10、transmitted flux rr is given by the equation Qtr = Q. e-kb where e is the base of natural logarithms; k is a linear absorption coefficient. This equation is derived from integration of the differential equation d, = - k,dx where x varies from 0 to b, dr, is the reduction in radiant energy flux along
11、 an infinitely small optical path length dx, and !I transmis- Logarithm (to base ten) of the reciprocal sion (optical) density of the transmittance A A=lgl (CIE 45-20-100) T 6 absorbed flux without Difference between the incident and phenomena other than transmitted flux a 00 - tr W absorption 7 abs
12、orption Transformation of radiant energy to a (CIE 45-05-070) different form of energy by interaction with matter 8 absorptance Ratio of the absorbed radiant (luminous) a (CIE 45-20-115) flux to the incident flux a x 9 internal transmittance Ratio of the radiant (luminous) flux (of a homogenous non-
13、 reaching the exit surface of the layer to diffusing layer) the flux which leaves the entry surface 5, (CIE 45-20-090) 10 internal absorbance; internal transmission density (CIE 45-20-105) Logarithm (to base ten) of the reciprocal of the internal transmittance Ai Ai = lg 1 i 11 internal absorptance
14、Ratio of the radiant (luminous) flux (of a homogenous non- absorbed between the entry and the diffusing layer exit surfaces of the layer to the flux ai (CIE 45-20-120) which leaves the entry surfaces 1) The definition or this term, used, but not defined, in the Vocabulaire international de Ibclairag
15、e (International lighting vocabulary) has been deduced from the definitions which follow it. NOTE - The references between parentheses are those of publication CIE No. 38, Vocabulaire internationale de / partial internal transmission density21 The ratio, expressed as a percentage, of the sample flux
16、 to the reference flux Fraction of the internal absorbance of a solution due to certain of its consti- tuents. The absorbance of a solution for given experimental conditions is thus the difference between its internal absorb- ance and that of the solution used as reference 100: I Ig; s characteristi
17、c partial internal absorbance; characteristic partial internal transmission density21 The partial internal absorbance of a solution due to only one of its con- stituents (for example compound dissolved for analysis) lg.; s 21 concentration Ratio of the mass of compound dissolved to the volume of the
18、 solution According to the units used, one can dif- ferentiate 21.1 and 21.2 !l.l mass concentration Ratio of the mass of the compound dissolved to the volume of the solution 21 .i - amount-of-substance concentration Ratio of the amount-of-substance of compound dissolved to the volume of the solutio
19、n International symbol for unit mm or cm mm or cm W W kg/m3 mol/l 1) Terms 12 and 13 are equivalent when the incident light ray is normal. The product of the optical path length and the refractive index of the absorbing solution is called the “chemin optique” (literally “optical path”). 2) The terms
20、 “partial internal transmission density” and “characteristic partial internal transmission density” are obsolete. 3 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 62
21、86-1982 (E) Table 2 koncluded) No. Term Definition Symbol Formula International symbol for unit 22 characteristic partial Characteristic absorbance per unit internal absorbance thickness and per unit concentration of coefficient the dissolved compound under con- sideration NOTE - By extension, and i
22、n general, the con- centration used is often that of the element or molecule being determined. According to the units used, one can dif- ferentiate 22 1 and 22.2 22.1 specific mass absorbance Absorbance coefficient for which the coefficient thickness is usually expressed in cen- timetres and the con
23、centration in grams a AC re cm-f.g-l,l of compound dissolved in one litre of solution 22.2 specific molar absorbance coefficient 1) Absorbance coefficient for which the thickness is usually expressed in cen- timetres and the concentration in moles of compound dissolved in one litre of solution 4 cm-
24、l.mol-1.1 -the measurement wavelength I, in nanometres; -the nature of the solvent; -the value x of the term in question with its subscript or unit, if necessary. Example : For specific mass absorbance coefficient 540 b) c x subscript or unit at t “C, I nanometres, solvent Example : For specific mas
25、s absorbance coefficient 2 200 cm-1.9-1.1 at 20 OC, 540 nm, in aqueous solution 4 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 6286-1982 (EI 3.2 Beers law The radi
26、ant flux of a beam of parallel monochromatic radiation decreases exponentially as the concentration of the absorbing compound increases, all other factors being constant : atr = G+, e-km Q or = 0 e-4 c where e is the incident flux; Qtr IS the transmitted flux; e is the base of natural logarithms; k,
27、 and k, are absorption coefficients which are constant for given experimental conditions; e C is the mass concentration; is the amount of substance concentration. 3.3 Additive nature of the laws of Lambert-Bouguer and Beer When a beam of parallel monochromatic radiation traverses, at normal incidenc
28、e, an absorbing medium with plane, parallel surfaces and which is homogeneous, isotropic, non- luminescent, and non-scattering, and consists of a solution of n dissolved compounds which do not react with one another, the total absorbance is equal to the sum of the n characteristic ab- sorbances. 3.4
29、 General law The laws of Lambert-Bouguer and Beer can be expressed by a single equation : Qtr = !Do lo- abQ or Qtr = o lo- 6 is the optical path length; E is the specific molar absorbance coefficient which is constant for given experimental conditions; e, Qtr, e and c have the same meanings as in 3.
30、2. In practice, absorbances are generally measured so that the characteristic absorbance of the dissolved compound under consideration can be obtained by applying the additive law (see 3.3) in the form A, - A, = A, = abe = Ebc where A, is the absorbance of solution 1; A2 is the absorbance of solutio
31、n 2; A, is the characteristic absorbance of the dissolved com- pound under consideration; a, 6, c, E and Q have the same meanings as in 3.2 and in the previous equation. 4 Apparatus Sub-clause 4.1 is intended to facilitate understanding of the objectives mentioned in clause 1 and which are detailed
32、in 4.2 and 4.3. 4.1 Components of molecular absorption spectrometers The components which make up molecular absorption spec- trometers, i.e. instruments designed for the determination of absorbance or percentage transmittance, are intended to assure the three following functions : a) production of a
33、 beam of radiation of a selected band of wavelengths and control of the bandwidth; b) introduction of the solution to be examined into the beam of radiation; c) measurement. To the three fundamental units assuring these three functions, one must add various associated devices (collimators, lenses, f
34、ixed or rotating mirrors, diaphragms, slits, etc.) which define the beam appropriately in space and direct it onto the various parts of these units. A wavelength scale system, the graduations of which may cor- respond to wavelength mm) or to wave number (cm-t), com- pletes the instrument. 4.1.1 Devi
35、ces for the production of a beam of radiation The beam of radiation is characterized by its spectral compos- ition, its intensity, its configuration and its direction in space; consequently, its production involves a source of radiation, a selector of the wavelengths emitted, and various complemen-
36、tary devices. The spectral characteristics of an instrument are not directly related to any one of these parts but result from their associa- tion. 5 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted w
37、ithout license from IHS-,-,-IS0 6286-1982 (El 4.1.1.1 Sources of radiation 4.1.1.3 Complementary devices Sources of radiation are differentiated principally by the emis- sion spectra they produce. Such a spectrum may, in fact, cover a range of wavelengths, more or less expanded, and show a continuou
38、s or discontinuous profile with, as the case may be, bands of various width or line emissions, For example, a tungsten filament lamp emits a continuous spectrum in the visible and near infra-red. Other examples are a hydrogen lamp emitting a continuous spectrum in the ultra- violet and metal vapour
39、lamps (Hg, Na, Cd, etc.) which, under certain conditions, emit a line spectrum. An instrument may be equipped with one or more sources. Some types of sources of continuous radiation are associated with interferometers in order to obtain a temporal programming of the emission of radiation; this resul
40、ts in a particular exploita- tion of the signals received by the detector (Fourier transforma- tion technique). This technique eliminates the need for wavelength selectors (4.1.1.2). 4.1 .I .2 Wavelength selector This is the part of the instrument comprising one or more devices which allow the isola
41、tion of a range of wavelengths from the spectrum emitted by the radiation source. An entrance slit and an exit slit are associated with these devices, depending on the circumstances. These devices (which may be used singly, alternatively, or together in the same apparatus) may be classified accordin
42、g to the phenomena to which they relate : a) absorbing filters, the function of which is based on the selective absorption of certain radiations; b) interference filters, the function of which is based on the interference of radiation: c) prisms and gratings, the function of which is based on the di
43、spersion of radiation (the term “monochromator” is often used to designate a selection device to isolate a nar- row wavelength region). These devices may equally well be grouped into two categories according to their method of use : - fixed pass band selectors, generally known as filters : the chang
44、e from one wavelength to another is effected by placing a different filter in the path of the beam. Each filter corresponds to a definite wavelength band; - selectors for continuous variation of wavelength, which are known as prisms, gratings and adjustable interference filters : a mechanical device
45、 works so that the different rays that they separate are dispersed in a con- tinuous way (with reference to the exit slit when this is pro- vided). The exit slit of the selector is often adjustable and is generally adjusted so that it is of the same width as the entrance slit; its width is one of th
46、e parameters upon which the spectral purity of the measuring beam depends. These are the parts of the apparatus which give the radiation beam the appropriate spatial definition, i.e. cross-section, parallelism, focus, path-type (single or double beam) etc. Various devices, such as collimators, lense
47、s, fixed or rotating mirrors, diaphragms and slits, are used for this purpose. 4.1.2 Devices for introducing the solution In order to intercept the measuring beam, solutionsaregenerally introduced in a transparent vessel called an “optical cell” or more simply “cell”. There are several versions whic
48、h differ in their geometry, and which allow for intermittent or continuous introduction of the solutions for measurement. The simplest are hollow rectangular prisms. The cells are usually supported and positioned by cell carriers which, in instruments for the visi- ble and ultraviolet regions, are p
49、ositioned after the wavelength selector. The compartment in which the cell carrier is mounted is, according to the design of the instrument, more or less totally shaded from ambient light and can be equipped with ancillary devices such as thermal conditioning, cell-changer, etc. 4.1.3 fvleasurement system The conversion of the information contained within the emergent beam into signals which are intelligible to the user of the instrument (excluding electronic stabilization devices) involves : a) reception
