ISO-6767-1990.pdf
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1、INTERNATIONAL STANDARD IS0 6767 First edition 1990-09-01 Ambient air - Determination of the mass concentration of sulfur dioxide - Tetrachloromercurate (TCM)/pararosaniline method Air ambiant - D in annex B, a determination is given for the mass concentration of sulfur dioxide present in the sodium
2、disuifite solution used for routine checks; in annex C, a method is given for the recovery of mercury from fresh and used solutions. iii Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/2
3、2/2007 21:22:23 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD IS0 6767:1990(E) Ambient air - Determination of the mass concentration of sulfur dioxide - Tetrachloromercurate (TCM)/pararosaniline method 1 Scope This international Standard specifies a
4、 spectro- photometric method, known as the tetrachioro- mercurate (TCM)/pararosaniline method, for the de- termination of the mass concentration of sulfur di- oxide in ambient air within the range of 20 ug/me to about 500 i.rg/m3. The sampling period is 30 min to 60 min. if a longer sampling period
5、than 60 min is used, or higher concentrations of sulfur dioxide (up to about 2000 ug/ms) are expected, care is necessary to en- sure that the concentrations of sulfur dioxide in the absorption solution given in clause 6, paragraph 2 are not exceeded. This can be achieved by a re- duction of the volu
6、me flow rate during sampling. Sample solutions obtained by this procedure may be stored for up to 24 h before making measure- ments, provided that they are kept in a refrigerator at about 5 “C. Substances which are known to interfere and which might be present in the air being sampled are listed in
7、7.5 indications of the precision and accuracy of the method, and of the lower detection limit are given in 8.2. Detection limit, standard deviations and lnterfer- ences qualify the TCM-method for orientating field measurements in the higher concentration range. When more accurafe measurements are ne
8、cessary, instruments which are specially tested and caii- brated should be used. 2 Normative references cation, the editions indicated were valid. Ail stan- dards are subject to revision, and parties to agreements based on this international Standard are encouraged to investigate the possibility of
9、ap- plying the most recent editions of the standards in- dicated below. Members of IEC and IS0 maintain registers of currently valid international Standards. IS0 4219:1979, Air quality - Determination of gaseous sulphur compounds in ambient air - Sam- pling equipment. IS0 6349:1978, Gas analysis - P
10、reparation of cali- bration gas mixtures - Permeation method. 3 Principle Absorption of sulfur dioxide present in the air sample by passage through a sodium tetra- chioromercurate (TCM) solution within a specified period resulting in the formation of a dichioro- sulfitomercurate complex. Destruction
11、 of any nitrite ions formed in the sodium tetrachioromercurate solution, by nitrogen oxides present in the air sample, by adding suifamic acid solution, Conversion of the dichiorosuifitomercurate complex into intensely violet coioured pararosaniiine methyl suifonic acid, by adding a formaldehyde sol
12、ution and acidified pararosaniiine hydrochloride soiutionartro the resuit- ant solution. Determination of the absorbance of the sample soi- ution at a wavelength of about 550 nm using an ap- propriate spectrophotometer (or coiorimeter) and calculation of the mass concentration of sulfur diox- ide by
13、 means of a calibration graph prepared using calibration gas mixtures. The following standards contain provisions which, Depending on the the equipment available in the through reference in this text, constitute provisions laboratory, it- may be convenient to use sodium of this international Standar
14、d. At the time of publi- disulfite solutions for routine checks. However, the 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:22:23 MDTNo reproduction or networking permitte
15、d without license from IHS -,-,- IS0 6767:1990(E) solutions are only used after proper calibration us- ing a permeation device. between a degree of purity of 100 % and the degree of purity obtained, add an additional 0,2 ml of PRA stock solution before making up to the mark with 4 Reagents water. Du
16、ring the analysis, use only reagents of recognized analytical grade and only distilled water, preferably double-distilled water, or water of equivalent purity, free from oxidants. WARNING - Use the reagents in accordance with the appropriate health and safety regulations. 4.3 Formaldehyde, approxima
17、tely 2 g/i solution. Pipette 5 ml of a commercially available 36 % (m/m) to 38 % (m/m) formaldehyde (HCHO) solution into a 1000 ml one-mark volumetric flask. Make up to the mark with water and mix well. Prepare this solution on the day of use. 4.1 Sodium tetrachloromercurate (TCM), absorp- tion solu
18、tion, c(Na,HgCid) = 0,04 mot/i. 4,4 Sulfamic acid, 6 g/i solution. - .- Dissolve IO,9 g of mercury(ii) chloride (HgCi,), 4,7 g of sodium chloride (NaCI) and 0,07 g of ethylene- dinitrilo tetraacetic the value obtained when dividing f by the volume, in cubic metres, of air sampled during the calibrat
19、ion procedure according to 7.1, shall differ by less than 10 % from the calibration factor fob- tained with calibration gas mixtures. 7.3 Determination 7.3.1 Leave the sample (clause 6) for at least 20 min after sampling to allow trapped ozone to de- compose. Then transfer the sample solution quanti
20、tatively to a 25 ml one-mark volumetric flask, using about 5 ml of water for rinsing. 7.3.2 Add 1 ml of the suifamic acid solution (4.4) to each flask and allow to react for 10 min to destroy the nitrites from oxides of nitrogen. Then pipette 2,0 ml of the formaldehyde solution (4.3) followed by 5 m
21、l of the pararosaniiine reagent (4.2.4) into the flasks. Make up to the mark with freshly boiled and cooled distilled water and store at 20 “C + 1 “C. Using the spectrophotometer or coiorimeter (5.2) measure the absorbance of the sample solution and the zero member solution, against distilled water
22、in the reference cell, between 30 min and 60 min after the addition of the reagents and Immediately after filling the ceils. Do not allow the coloured solutions to remain in the ceil as a coioured film will be deposited on the in- side wails. NOTE 2 Fixed time intervals between the addition of each
23、reagent, for example 1 min, ensure a better reproducibility of the formation of the absorbing com- pound. 7.4 Preparation of the blank solution Prepare a blank by pipetting 10 ml of unexposed absorption solution (4.1) Into a 25 ml one-mark volumetric flask, add the reagents as before, treat the solu
24、tion as described in 7.3.2 and read the absorbance against distilled water using 1 cm ceils. Compare this value with the one recorded for the zero member solution obtained when preparing the calibration graph (7.1). Differences of more than 10 % between the two values indicate contam- ination of the
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