1、BRITISH STANDARD BS ISO 6768:1998 Ambient air Determination of mass concentration of nitrogen dioxide Modified Griess-Saltzman method ICS 13.040.20BSISO6768:1998 This British Standard, having been prepared under the direction of the Health and Environment Sector Board, was published under the author
2、ity of the Standards Board and comes into effect on 15 October 1998 BSI 04-1999 ISBN 0 580 30470 1 National foreword This British Standard reproduces verbatim ISO6768:1998 and implements it as the UK national standard. It supersedes BS1747-8:1986 which is withdrawn. The UK participation in its prepa
3、ration was entrusted by Technical Committee EH/2, Air quality, to Subcommittee EH/2/3, Ambient atmospheres, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change,
4、 and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international or Eu
5、ropean publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the ne
6、cessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the
7、ISO title page, page ii, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date Comme
8、ntsBSISO6768:1998 BSI 04-1999 i Contents Page National foreword Inside front cover Foreword ii 1 Scope 1 2 Normative reference 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Sampling 4 7 Procedure 4 8 Expression of results 6 9 Test report 6 Annex A (informative) Bibliography Inside back cover Figure 1
9、 Examples of sampling trains capable of the determination of the mass concentration of nitrogen dioxide in ambient air 2 Figure 2 Examples of absorbers suitable for sampling nitrogen dioxide 3 Figure 3 Typical calibration graph 5ii blankBSISO6768:1998 ii BSI 04-1999 Foreword ISO (the International O
10、rganization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been estab
11、lished has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardizat
12、ion. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75% of the member bodies casting a vote. International Standard ISO 6768 was prepared by Technical Committee I
13、SO/TC146, Air quality, Subcommittee SC3, Ambient atmospheres. This second edition cancels and replaces the first edition (ISO6768:1985), which has been technically revised. Annex A of this International Standard is for information only. Descriptors: Air, quality, air pollution, chemical analysis, de
14、termination of content, nitrogen dioxide, concentration.BSISO6768:1998 BSI 04-1999 1 1 Scope This International Standard specifies a modified Griess-Saltzman method for the determination of the mass concentration of nitrogen dioxide present in ambient air. The method is applicable to the determinati
15、on of the mass concentration of nitrogen dioxide present in ambient and confined air within the range0,003mg/m 3to 2mg/m 3and for sampling times between 10min and 2h. Substances present in the air mass under investigation, and thus in the air sample, and known to have an effect on the instrument rea
16、ding, are given in7.4. Information on the performance characteristics is given in8.2. The method is not suitable for personal breathing-zone sampling. The Griess-Saltzman method is suitable for the analytical check of calibration gas mixtures which are used to calibrate chemiluminescence analysers (
17、see ISO7996). 2 Normative reference The following standard contains provisions which, through reference to this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements ba
18、sed on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 6349:1979, Gas analysis Preparation of calibration gas mixtu
19、res Permeation method. 3 Principle The nitrogen dioxide present in an air sample is absorbed by passage through an azo-dye-forming reagent within a specified period, resulting in the formation of a pink colour within 15min. The absorbance of the sample solution is then determined at a wavelength bet
20、ween 540nm and550nm using an appropriate spectrophotometer. The corresponding mass concentration of nitrogen dioxide is determined from a calibration graph of absorbance vs. concentration prepared using sodium nitrite solutions of known concentrations. 4 Reagents During the analysis, use only reagen
21、ts of recognized analytical grade and only nitrite-free water (4.1). 4.1 Nitrite-free water. If the water used to prepare the absorption and calibration solutions results in a pink coloration due to the presence of nitrite in the water, prepare nitrite-free water as follows. Add one crystal each of
22、potassium permanganate (KMnO 4 ) and barium hydroxide Ba(OH) 2 to the water and redistill using an all-glass still. 4.2 N-(1-naphthyl)ethylenediamine dihydrochloride, 0,5g/l stock solution. Dissolve 0,5g of N-(1-naphthyl)ethylenediamine dihydrochloride C 10 H 7 NH(CH 2 ) 2 NH 2 2HCl in1000ml of nitr
23、ite-free water (4.1). Store in a stoppered brown glass bottle at a temperature below 5C. The solution is stable for several months. NOTEIt is also possible to store small weighed amounts of the solid reagent. 4.3 Absorption solution. Dissolve 5,0g of sulfanilic acid (C 6 H 4 SO 3 HNH 2 ) in approx.
24、600ml of nitrite-free water (4.1) and 50ml of acetic acid by heating, if necessary, in a 1000ml one-mark volumetric flask. Cool the solution to room temperature, add 100ml of N-(1-naphthyl)ethylenediamine dihydrochloride solution (4.2), mix and make up to the mark with nitrite-free water(4.1) Store
25、in a well-stoppered brown glass bottle at a temperature below 5C. The solution is stable for2weeks. 4.4 Gas mixtures. Prepare gas mixtures, which are used to test the absorption efficiency (7.1.1), following the permeation technique specified in ISO6349 or by an equivalent method. 4.5 Reagents for p
26、reparation of the calibration graph. 4.5.1 Nitrite solution,= 250mg/l. Dissolve 375mg of sodium nitrite (NaNO 2 ) in nitrite-free water (4.1) in a 1000ml one-mark volumetric flask. Make up to the mark with nitrite-free water and mix well. Store in a well-stoppered bottle. The solution is stable for
27、at least 3 months. 1ml of this solution contains 2504g of NO 2 . 4.5.2 Nitrite solution,= 2,5mg/l. Transfer 10,0ml of nitrite solution (4.5.1) to a1000ml one-mark volumetric flask. Make up to the mark with nitrite- free water (4.1) and mix well. Prepare this solution immediately before use. 1ml of t
28、his solution contains 2,54g of NO 2 . NO 2 NO 2BSISO6768:1998 2 BSI 04-1999 5 Apparatus 5.1 Ordinary laboratory apparatus and sampling equipment, as specified in5.1.1 to5.1.7. 5.1.1 Sampling probe. Borosilicate glass, stainless steel or polytetrafluoroethylene tube whose internal diameter is approxi
29、mately 6mm and which is as short as possible, but in any case not longer than2m, provided with a downward-facing air intake. If the use of such short sampling probes is not possible, an auxiliary sampling pipe consisting of a sampling probe of internal diameter about 50 mm, provided with a joint for
30、 attachment to the sampling train, and a pump drawing air at a volume flowrate of about 2m 3 /h shall be used seeFigure 1c). 5.1.2 Cotton wool filter. Borosilicate glass tube, of internal diameter atleast15mm and length approximately 80mm, loosely packed with bleached, not optically brightened, and
31、non-finished cotton wool. It shall be a component of the sampling train only if it is considered necessary to remove ozone from the air before it enters the fritted bubbler (see also7.4). Figure 1 Examples of sampling trains capable of the determination of the mass concentration of nitrogen dioxide
32、in ambient airBSISO6768:1998 BSI 04-1999 3 5.1.3 Fritted bubbler. Borosilicate all-glass bubblers equipped with a frit whose porosity shall be fine enough to enable an absorption efficiency of at least 0,95 to be attained without providing too great a pressure drop in use. Frits having pore diameter
33、s between 404m and604m are suitable. Four examples of fritted bubblers (types A to D) that have been found to be suitable are shown inFigure 2. The absorption efficiency of each individual fritted bubbler shall be tested at least once a year using calibration gas mixtures prepared following the perm
34、eation technique specified in ISO6349 or by an equivalent method. Coloured frits shall be cleaned with a mixture of a potassium dichromate solution and concentrated sulfuric acid or other appropriate cleaning agents. When a dichromate-sulfuric acid mixture is used, care shall be taken that the frits
35、 are thoroughly rinsed with nitrite-free water (4.1). WARNING Avoid physical contact with dichromate and reagents containing dichromate, in particular with a dichromate-sulfuric acid mixture. 5.1.4 Trap. Conical flask of capacity 100ml, filled with glass-wool. 5.1.5 Membrane filter. 5.1.6 Sampling p
36、ump and control system, capable of drawing air at a volume flow rate of about 0,4l/min to 0,6l/min during the sampling period. 5.1.7 Air metering device. Use either a wet test meter, a calibrated all-glass variable-area flowmeter, a calibrated critical orifice or a calibrated mass flowmeter. In all
37、cases, the air volume flowrate should be known to within 5%. Figure 2 Examples of absorbers suitable for sampling nitrogen dioxide (The ends of the glass tubes of each of these absorbers can be designed as spherical ground joints, conical ground joints or olives.)BSISO6768:1998 4 BSI 04-1999 A wet t
38、est meter or a soap bubble meter is convenient for testing the calibration of the variable-area flowmeter, the critical orifice or the mass flowmeter. 5.2 Spectrophotometer, capable of determining absorbance at a wavelength of between 540nm and550nm, and capable of taking optical cells for spectroph
39、otometric measurements of liquids as specified in5.3. 5.3 Optical cells, plane, matched pairs, having an optical pathlength of 10mm to 50mm. 5.4 One-mark pipettes, of capacities 5ml; 10ml; 15 ml; 20ml; 25ml; 50ml. 6 Sampling Assemble a sampling train in accordance with the examples shown inFigure 1
40、and any special requirements for the air mass under investigation. Use ground glass joints upstream from the fritted bubbler or butt-to-butt glass with polyvinylchloride or polytetrafluoroethylene connections. Transfer, by means of a pipette (5.4), a suitable volume of absorption solution (4.3) into
41、 the dry fritted bubbler (5.1.3), namely 25ml for fritted bubblers of type A, 20ml for fritted bubblers of typeB, 50ml for fritted bubblers of type C and10ml for fritted bubblers of type D. Connect the fritted bubbler to the sampling train. Record the reading on the wet test meter (5.1.7) and the ti
42、me, and start the sampling pump (5.1.6). Adjust the air-volume flow regulator to give an air- volume flowrate of about 0,4l/min to 0,6l/min. The sampling period shall be 10min to 2h as required. Protect the absorption solution from light during sampling. At the end of the sampling period, switch off
43、 the sampling pump, note the reading on the wet test meter and the time. Remove the fritted bubbler from the sampling train. Mix the bulk of the sample solution outside the frit with the small quantity of the sample solution inside the frit by sucking a sufficient portion through the frit and then r
44、eleasing. Repeat several times. Stopper the fritted bubbler carefully and protect the sample solution from light. Allow the sample solution to stand for 15min. Due to the limited time stability of the sample solution, the interval of time between the end of sampling and the beginning of measurements
45、 to be carried out with the sample solution shall not exceed 20h. NOTEGenerally, the influence of evaporation can be neglected for short sampling periods. However, with an extended sampling period, a small volume of absorption solution and dry air conditions, the influence of evaporation should be t
46、aken into account. 7 Procedure 7.1 Test of fritted bubblers 7.1.1 Test of absorption efficiency In accordance with the examples shown inFigure 1, assemble a sampling train where two fritted bubblers of the same type are connected in series, each of them containing the appropriate volume of absorptio
47、n solution, as specified in clause6. Introduce the inlet of the sampling train into the outlet of a permeation device (or use an equivalent method) capable of producing gas mixtures (see4.4) at a volume flowrate higher than that expected at the intake area of the sampling train. Prepare a gas mixtur
48、e having a mass concentration of nitrogen dioxide of about 1mg/m 3 . Avoid mass concentrations of nitrogen dioxide higher than 2mg/m 3 . Choose a sampling period resulting in the absorption of a mass of nitrogen dioxide of about0,54g per 1ml of the absorption solution exposed in the first fritted bu
49、bbler, and carry out sampling as specified in clause6. Calculate the absorption efficiency by dividing the absorbance of the sample solution in the first fritted bubbler by the sum of the absorbances of the sample solution in the first and the second fritted bubbler. The absorption efficiency shall be at least 0,95. Fritted bubblers that do not meet this requirement should not be used. 7.1.2 Test of frit porosity The porosity of the frits may be affected by repeated cleaning. Therefore, the frits shall be checked, for example, using a su
