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1、INTERNATIONAL STANDARD IS0 8761 First edition 1989-12-01 Work-place air - Determination of mass concentration of nitrogen dioxide - Method using detector tubes for short-term sampling with direct indication Air des lieux de travail - D in applications re- quiring better precision or freedom from int
2、erfer- ences, the use of classical chemical or instrumental methods is recommended. The method is suitable for personal, breathing-zone sampling as well as for the general area sampling. 2 Normative reference The following standard contains provisions which, through reference in this text, constitut
3、e provisions of this tnternational Standard. At the time of publi- cation, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encour- aged to investigate the possibility of applying the most recent edition of the
4、 standard indicated below. Members of IEC and IS0 maintain registers of cur- rently valid International Standards. IS0 6879:1983, Air quality - Performance character- istics and related concepts for air quality measuring methods. 3 Definitions For the purposes of this International Standard, the fol
5、lowing definitions apply. 3.1 length-of-stain detector tube: A tube containing a reagent which reacts rapidly with nitrogen dioxide present in the air sample, producing a sharply de- fined interface between reacted and unreacted rea- gent system. 3.2 volume per stroke: The amount of air or other gas
6、 mixture drawn by the detector-tube pump during the opening time per stroke. 3.3 opening time per stroke: The time taken for one complete cycle of the detector-tube pump air cham- ber. 4 Principle Reaction of nitrogen dioxide present in the air sam- ple passing through a detector tube within a given
7、 period with reagents coated on a solid support con- tained in the tube, resulting in the formation of a coloured reaction product which provides a sharply defined stain in the tube. Determination of the mass concentration of nitrogen dioxide by comparing the observed length of stain developed to le
8、ngths of stain prepared using cali- bration gas mixtures, taking into account the effect of interferents on the instrument reading and the correction factors for pressure, temperature and relative humidity. 5 Reactions and interferents Several colour-producing reactions by which nitro- gen dioxide c
9、an be detected are known. The follow- ing are used In detector tubes. 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100 Not for Resale, 04/24/2007 10:37:26 MDTNo reproduction or networking permitted without licens
10、e from IHS -,-,- IS0 8761:1989(E) 5.1 NJ -diphenylbenzldine reaction Tubes containing a reagent system based on NJ -diphenyl-benzidine are length-of-stain detector tubes; the change of intensity of colour is from grey to blue-grey. 5,l.l Reaction equation NO,+CGHS-NH-C,H4-CGH4-NH-C,HS -+ coloured co
11、mpounds 5,1,2 lnterferents Chlorine and ozone produce stains similar to those produced by nitrogen dioxide, but with lower sensi- tivity. For example, at the mass concentration of chlorine of 3 mg/ms, a length of stain corresponding to the length of stain at the mass concentration of nitrogen dioxid
12、e of 0,8 mg/m3 is produced; at the mass concentration of chlorine of 6 mg/ms, a length of stain corresponding to the length of stain at the mass concentration of nitrogen dioxide of I,6 mg/ms is produced: and at the mass concen- tration of ozone of 2 mg/ms, a length of stain corre- sponding to the l
13、ength of stain at the mass concentration of nitrogen dioxide of 0,4 mg/ms is produced. 5.2 N-(I-naphthyl)-ethylenediamine dlhydrochloride reaction Tubes containing a reagent system based on N-(I-naphthyl)-ethylenediamine dihydrochloride are length-of-stain detector tubes: the change of inten- sity o
14、f colour is from white to red. 5.2.1 Reaction equation NO*+C,H,-NH-CH2-CH2-NH*, PHCI+ +H*N-C,Hd-SO,H + diazo complex 5,2,2 lnterferents Chlorine and ozone are positive interferents. 5.3 o-Tolidine reaction Tubes containing a reagent system based on o-tolidine are length-of-stain detector tubes: the
15、change of intensity of colour is from white to yellow-orange. 5.3.1 Reaction equation N0,+NH2(CH,)C,H,-C,H,(CH,)NH* + coloured compounds 5,3,2 lnterferents Halogens and chlorine dioxide and most other oxidizing agents produce stains similar to that produced by nitrogen dioxide, Sulfur dioxide at mas
16、s concentrations greater than 100 mg/m3 bleach the stain produced by nitrogen dioxide. 6 Apparatus A complete measurement system consists of a compatible detector tube and detector-tube pump. These systems are normally calibrated and supplied by the same manufacturer. 6,l Detector tubes, containing
17、a reagent that is coated on a solid support and is suitable for a colour-producing reaction by which the mass con- centration of nitrogen dioxide present in the air at work places (work areas or stationary posts) can be determined, with measuring range approximately 1 mg/ms to greater than 50 mg/ms,
18、 within the ac- ceptable ranges of temperature, pressure and rela- tive humidity stated by the manufacturer. Use only detector tubes which a) are uniformly packed, i.e. uniform packing tightness with no obvious segregation; b) contain filling layers, the surfaces of which are perpendicular to the tu
19、be axis; c) are free from leaks; and, in addition, meet the following requirement: d) length-of-stain detector tubes shall be designed to have an inaccuracy of less than (additionally, for hand-operated detector tube pumps) the opening time per stroke ( 3.3) with a representative detector tube (6.1)
20、 attached to the detector-tube pump, in accordance with the manufacturer s instructions. Compare the measured values obtained with the corresponding calibration data of the detector-tube pump and the detector tube. If these data do not agree within the limits stated in 6.2 the detector-tube pump sha
21、ll be serviced or reconditioned. NOTE 3 The resistance to flow of the detector tube and thus the opening time per stroke differs according to the type of detector tube used. 8.2 Determlnation Immediately after completion of sampling, hold the used detector tube next to an unused detector tube (6.1)
22、against a white background in adequate light- ing, but not in direct sunlight, and proceed as spec- ified in 8.2.1 and 8.2.2. 8.2.1 Evaluation of detector tube indication The evaluation of the detector tube indication should be made only by a person trained and experienced in detector tube reading.
23、Evaluate the length of stain obtained by comparison with lengths of stain associated with known concen- trations of nitrogen dioxide, usually marked on the detector tube. Apply the following rules: a) if the leading edge of the stain is not sharply de- fined, take the reading at the point where slig
24、ht discoloration can just be distinguished from the colour of the unreacted reagent system; b) if the leading edge of the stain is not perpendic- ular to the detector tube axis, take the mean re- sulting from the shortest and the longest length of stain, provided that the difference between the shor
25、test and longest length of stain is not greater 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100 Not for Resale, 04/24/2007 10:37:26 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 8
26、781:1989(E) than 20 % of the mean. Discard the detector tube reading in cases where this requirement is not fulfilled. Record the concentration of nitrogen dioxide asso- ciated with the length of stain obtained. 8.2.2 Evaluation of correction factors The length of stain obtained and intensity of col
27、our developed may be a function of temperature, pres- sure and relative humidity of air sample and may also be affected by substances other than nitrogen dioxide present in the air sample. In some cases, the interfering effects shall be taken into account by applying correction factors. There- fore,
28、 evaluate, if necessary, correction factors ap- propriate for interpreting the detector tube reading, referring to, for example, correction factors supplied by the manufacturer of the detector tube. 8.3 Disposal of detector tubes Dispose of detector tubes with due regard to the toxic or corrosive re
29、agent or reaction products con- tained tn the tubes, and in accordance with the manufacturer s disposal instruction and national re- quirements. 9 Expression of results 9.1 Calculation The concentration of nitrogen dioxide in the air sample is given by the detector tube indication evaluated accordin
30、g to clause 8. This concentration shall be given as mass concentration p (NO,), ex- pressed in milligrams per cubic metre. NOTE 4 The mass concentration of nitrogen dioxide p(NO,), expressed in milligrams per cubic metre, is related to the volume concentration q(NOJ, expressed in parts per million (
31、1 ml per 10s ml), by the formula PWJ 46,0 xp 293,2 x = 24,05 x (0 f 273,2) x 101,3 x dN0,) 5,536 x p = x 0 + 273,2 v(NOS) where P e 460 24,05 is the pressure, in kiiopascais, of the air sample; is the temperature, in.degrees Celsius, of the air sample; is the molar mass, in grams per mole, of ni- tr
32、ogen dioxide; is the molar volume, in iitres per mole, of an ideal gas at 293,2 K and 101,3 kPa. At 293,2 K and 101,3 kPa, the conversion factors for ni- trogen dioxide are 1 wm = I,91 mg/ms 1 mg/ms - 052 ppm 9.2 Precision Relative errors in detector tube measurements are greater at the lower end of
33、 the measuring range than at the higher end. The maximum permissible random error, expressed as twice the relative standard deviation (coefficient of variation) of de- tector tube measurements specified in this Interna- tional Standard is rt: 25 % at the mass concentration level of nitrogen dioxide
34、of 6 mg/m3. Some of the major sources of variation in detector tube meas- urements are: a) b) cl variability of the internal diameter of the glass tubes; for example, a tolerance of +_ 0,l mm is a f 4 % variation in a 5 mm internal diameter de- tector tube: variability of the filling layer containin
35、g the rea- gent system for the colour-producing reaction: important parameters are, for example, purity and uniformity of distribution of the reagent sys- tem, uniformity of particle size and bulk density of the solid substrate, and alignment of the filling layer in the detector tube; variability of
36、 the air volume and air volume flow rate due to the how characteristics of the detector-tube pump. 10 Test report The test report shall include at least the following information: 4 b) cl d) e) 0 cl) identification data for the air sample; reference to this International Standard; location in which
37、the air sample was taken and whether personal or general area; identification of the manufacturer of the detector tube and detector-tube pump used, the man- ufacturer s detector tube batch number, and the detector tube expiry date; start time and end time of the sampling period; number of detector-t
38、ube pump strokes or volume of the air sample; temperature, pressure and relative humidity of the air sample; Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100 Not for Resale, 04/24/2007 10:37:26 MDTNo reproduction o
39、r networking permitted without license from IHS -,-,- IS0 8761:1989(E) h) interferents known or suspected to be present in the air sample; i) mass concentration of nitrogen dioxide, ex- pressed in milligrams per cubic metre, as deter- mined by the measurement with the detector tube; j) name of the p
40、erson who performed the meas- urement. The test report shall also contain, if available, the mass concentration of nitrogen dioxide, expressed in milligrams per cubic metre, as determined by a method other than measurements with detector tubes. 5 Copyright International Organization for Standardizat
41、ion Provided by IHS under license with ISO Licensee=Defense Supply Ctr/9960866100 Not for Resale, 04/24/2007 10:37:26 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 8761:1989(E) Annex A (normative) Calibration of detector tubes Detector tubes suitable for the determina
42、tion of the concentration of nitrogen dioxide present in the air at work places (work areas or stationary posts) as commercially available and specified in 6.1 have been calibrated by the manufacturer of the detector tubes using calibration gas mixtures, These shall be mixtures of nitrogen dioxide a
43、nd a complimentary gas (e.g. purified air or nitrogen). The composition of these mixtures shall be known within specified limits. At the request of the user, the manufacturer of the detector tubes shall supply the calibration data for the detector tubes. Therefore, recalibration of detector tubes is
44、 required only in exceptional cases. Recalibration of detector tubes can be carried out by the user of the detector tubes provided that staff trained and experienced in preparing calibration gas mixtures are available. Some remarks on carrying out the calibration of detector tubes specified in 6.1 a
45、re given below. Prepare calibration gas mixtures following one of the dynamic methods listed in annex B or, prefera- bly, by the use of permeation tubes in a dynamic gas flow mixing system. Prepare a zero gas and several gas mixtures at different concentration levels of ni- trogen dioxide within the
46、 accuracy of + 5 % cover- ing the working range, for example 2 mglme, 4 mg/m3, 6 mg/ms, 10 mg/ms, 20 mg/ms, 30 mg/m3 and 50 mg/me. NOTE 5 The concentration of nitrogen dioxide in the gas mixture generated should be independently verified by, for example a chemiiuminescence method. At each of the sel
47、ected concentration levels, take at least five samples as foflows: Test the detector-tube pump (6.2) for leaks by in- serting an unopened detector tube (6.1) into the inlet port of the detector-tube pump and then operating the detector-tube pump. No air should flow in the system. if air-flow occurs,
48、 as indicated by, for ex- ample, a movement of the detector-tube pump air chamber, leaks may be present in the detector-tube pump, and the detector-tube pump shall be exam- ined and repaired or replaced, as necessary. Also test for flow blockage by operating the detector-tube pump without a detector
49、 tube. The detector-tube 6 pump should operate freely. if not, examine and re- pair or replace the detector-tube pump. Break off both ends of the detector tube and connect the opened detector tube, with the prescribed orien- tation if applicable, to the device used for generating the calibration gas mtxture by a butt-to-butt glass joint with, for example, a polyvinyl chloride con- nection. insert the free end of the detector tube into t
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