《BS-6068-2.36-1989 ISO-7890-3-1988.pdf》由会员分享，可在线阅读，更多相关《BS-6068-2.36-1989 ISO-7890-3-1988.pdf（10页珍藏版）》请在三一文库上搜索。
1、BRITISH STANDARD BS 6068-2.36: 1989 ISO 7890-3: 1988 Water quality Part 2: Physical, chemical and biochemical methods Section 2.36 Spectrometric method for the determination of nitrate using sulphosalicylic acid UDC 556.11 + 614.777 + 628.1/.3 + 663.63:53/54 Licensed Copy: sheffieldun sheffieldun, n
2、a, Tue Dec 05 01:29:45 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.36:1989 This British Standard, having been prepared under the direction of the Environment and Pollution Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 29 September
3、 1989 BSI 06-1999 The following BSI references relate to the work on this standard: Committee reference EPC/44 Draft for comment 87/51929 DC ISBN 0 580 17681 9 Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:29:45 GMT+00:00
4、2006, Uncontrolled Copy, (c) BSI BS 6068-2.36:1989 BSI 06-1999i Contents Page National forewordii 1 Scope 1 2 Principle 1 3 Reagents 1 4 Apparatus 2 5 Sampling and samples 2 6 Procedure 2 7 Expression of results 3 8 Test report 3 Annex A (normative) The effect of other substances on this method Insi
5、de back cover Table 1 Conversion table 3 Table 2 Standard deviation of repeatability and reproducibility 4 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:29:45 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.36:1989 ii BSI 06-1999 National foreword This Section of BS 6068, which has
6、been prepared under the direction of the Environment and Pollution Standards Policy Committee, is identical with ISO 7890-3:1988 “Water quality Determination of nitrate Part 3: Spectrometric method using sulfosalicylic acid”. The international standard was prepared by subcommittee 2, Physical, chemi
7、cal and biochemical methods, of Technical Committee 147, Water quality, of the International Organization for Standardization (ISO) with the active approval and participation of the UK. NOTEThe tests described in this Section of BS 6068 should only be carried out in laboratories with suitable facili
8、ties and by suitably qualified persons with an appropriate level of chemical expertise and knowledge of the necessary safety precautions. Standard chemical procedures should be followed throughout. This British Standard is being published in a series of Parts subdivided into Sections that will gener
9、ally correspond to particular international standards. Sections are being, or will be, published in Parts 1 to 7, which together with Part 0, are listed below. Part 0: Introduction; Part 1: Glossary; Part 2: Physical, chemical and biochemical methods; Part 3: Radiological methods; Part 4: Microbiolo
10、gical methods; Part 5: Biological methods; Part 6: Sampling; Part 7: Precision and accuracy. Textual errors. When adopting the text of the international standard, the textual errors given below were discovered. They have been marked in the text and have been reported to ISO in a proposal to amend th
11、e text of the international standard. In clauses 3.6, 3.7, 3.8, 6.1, 6.3.1, 6.3.4, 7.1 and Table 2, “nitrate” should be read as “nitrate nitrogen”. In clause 7.1 insert the following for the final paragraph (and before Table 1): See Table 1 for conversion of AN to in milligrams per litre or c (NO3)
12、in millimoles per litre. A British Standard does not purport to include all the necessary 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. ANO 3 Summary of
13、 pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, 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 co
14、ver. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:29:45 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 7890-3:1988 (E) BSI 06-19991 1 Scope 1.1 Substance determined This part of ISO 7890 specifies a method for the determination of nitrate ion in water. 1.2 Type of sample The method is s
15、uitable for application to raw and potable water samples. 1.3 Range Up to a nitrate nitrogen concentration, AN of 0,2 mg/l using the maximum test portion volume of 25 ml. The range can be extended upwards by taking smaller test portions. 1.4 Limit of detection1) Using cells of optical path length 40
16、 mm and a 25 ml test portion volume the limit of detection lies within the range AN= 0,003 to 0,013 mg/l. 1.5 Sensitivity1) A nitrate nitrogen concentration of AN = 0,2 mg/l gives an absorbance of about 0,68 unit, using a 25 ml test portion and cells of optical path length 40 mm. 1.6 Interferences A
17、 range of substances often encountered in water samples has been tested for possible interference with this method. Full details are given in Annex A. The main potential interferents are chloride, orthophosphate, magnesium and manganese(II), as shown in Annex A. Other tests have shown that this meth
18、od will tolerate a sample colour of up to 150 mg/l Pt providing the test portion absorption correction procedure is followed. (See 6.5.) 2 Principle Spectrometric measurement of the yellow compound formed by reaction of sulfosalicylic acid (formed by addition to the sample of sodium salicylate and s
19、ulfuric acid) with nitrate and subsequent treatment with alkali. Disodium dihydrogen ethylenedinitrilotetraacetate (EDTANa2) is added with the alkali to prevent precipitation of calcium and magnesium salts. Sodium azide is added to overcome interference from nitrite. 3 Reagents During the analysis,
20、use only reagents of recognized analytical grade, and only distilled water or water of equivalent purity. 3.1 Sulfuric acid, c(H2 SO4) . 18 mol/l, A = 1,84 g/ml. WARNING When using this reagent, eye protection and protective clothing are essential. 3.2 Glacial acetic acid, c(CH3COOH) . 17 mol/l, A =
21、 1,05 g/ml. WARNING When using this reagent, eye protection and protective clothing are essential. 3.3 Alkali solution, ANaOH = 200 g/l, = 50 g/l. Cautiously dissolve 200 g 2 g of sodium hydroxide pellets in about 800 ml of water. Add 50 g 0,5 g of disodium dihydrogen ethylenedinitrilotetraacetate d
22、ihydrate (EDTANa2) CH2-N(CH2COOH)CH2-COONa2.2H2O and dissolve. Cool to room temperature and make up to 1 litre with water in a measuring cylinder. Store in a polyethylene bottle. This reagent is stable indefinitely. WARNING When using this reagent, eye protection and protective clothing are essentia
23、l. 3.4 Sodium azide solution, = 0,5 g/l. Carefully dissolve 0,05 g 0,005 g of sodium azide in about 90 ml of water and dilute to 100 ml with water in a measuring cylinder. Store in a glass bottle. This reagent is stable indefinitely. WARNING This reagent is very toxic if swallowed. Contact between t
24、he solid reagent and acids liberates very toxic gas. NOTESulfamic acid solution, = 0,75 g/l, may be used as an alternative to sodium azide solution. 3.5 Sodium salicylate solution, = 10 g/l. Dissolve 1 g 0,1 g of sodium salicylate (HO-C6H4-COONa) in 100 ml 1 ml of water. Store in a glass or polyethy
25、lene bottle. Prepare this solution freshly on each day of operation. 1) Information derived from a United Kingdom interlaboratory test involving four participants. Limit of detection was taken as 4,65 times the within- batch standard deviation of the blank. A CH2-N CH2COOH()CH2-COONa2.2H2O ANaN 3 AN
26、H 2.SO3H AHO-C 6H4-COONa Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:29:45 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 7890-3:1988 (E) 2 BSI 06-1999 3.6 Nitrate2), stock standard solution, AN = 1 000 mg/l. Dissolve 7,215 g 0,001 g of potassium nitrate (KNO3) (previously dried at 105
27、 C for at least 2 h) in about 750 ml of water. Quantitatively transfer to a 1 litre one-mark volumetric flask and make up to volume with water. Store the solution in a glass bottle for not more than 2 months. 3.7 Nitrate2), standard solution, AN = 100 mg/l. Pipette 50 ml of the stock standard soluti
28、on (3.6) into a 500 ml one-mark volumetric flask and make up to the mark with water. Store the solution in a glass bottle for not more than 1 month. 3.8 Nitrate2), working standard solution, AN = 1 mg/l. Into a 500 ml one-mark volumetric flask, pipette 5 ml of standard nitrate solution (3.7). Make u
29、p to volume with water. Prepare the solution freshly on each occasion of use. 4 Apparatus Usual laboratory apparatus, and 4.1 Spectrometer, capable of operating at a wavelength of 415 mm and equipped with cells of optical path length 40 mm or 50 mm. 4.2 Evaporating dishes, about 50 ml capacity. If t
30、he dishes are new, or not in regular use, they shall first be thoroughly rinsed with water and taken through the procedure in the first two paragraphs of 6.3.2 to clean them. 4.3 Water bath, boiling, capable of accepting at least six of the evaporating dishes (4.2). 4.4 Water bath, capable of thermo
31、static regulation to 25 C 0,5 C. 5 Sampling and samples Laboratory samples should be collected in glass bottles and should be analysed as soon as possible after collection. Storage of samples at between 2 C and 5 C may preserve many types of sample, but checks should be made to confirm this with eac
32、h sample type. 6 Procedure WARNING This procedure involves the use of concentrated sulfuric acid, acetic acid, sodium hydroxide and sodium azide solutions. Eye protection end protective clothing are essential when using these reagents. They must never be pipetted by mouth. 6.1 Test portion The maxim
33、um test portion volume which can be used for the determination of nitrate2) concentration up to AN = 0,2 mg/l is 25 ml. Use smaller test portions as appropriate in order to accommodate higher nitrate concentrations. Before taking the test portion, allow laboratory samples containing suspended matter
34、 to settle, centrifuge them or filter them through a washed glass fibre filter paper. Neutralize samples having a pH value greater than 8 with acetic acid (3.2) before taking the test portion. 6.2 Blank test Carry out a blank test in parallel with the determination, using 5,00 ml 0,05 ml of water in
35、stead of the test portion. Let the absorbance measured be Ab units. 6.3 Calibration 6.3.1 Preparation of the set of calibration solutions To a series of clean evaporating dishes (4.2), add, from a burette, 1; 2; 3; 4 and 5 ml respectively of the working standard nitrate2) solution (3.8), correspondi
36、ng to nitrate amounts of m(N) = 1; 2; 3; 4 and 5 g in the respective dishes. 6.3.2 Colour development Add 0,5 ml 0,005 ml of sodium azide solution (3.4), and 0,2 ml 0,002 ml of acetic acid (3.2). Wait for at least 5 min, and then evaporate the mixture to dryness in the boiling water bath (4.3). Add
37、1 ml 0,01 ml of sodium salicylate solution (3.5), mix well and evaporate the mixture to dryness again. Remove the dish from the water bath and allow the dish to cool to room temperature. Add 1 ml 0,01 ml of sulfuric acid (3.1) and dissolve the residue in the dish by gentle agitation. Allow the mixtu
38、re to stand for about 10 min. Then add 10 ml 0,1 ml of water followed by 10 ml 0,1 ml of alkali solution (3.3). Quantitatively transfer the mixture to a 25 ml one-mark volumetric flask, but do not make up to the mark. Place the flask in the water bath (4.4) at 25 C 0,5 C for 10 min 2 min. Then remov
39、e the flask and make up to the mark with water. 2) See national foreword for details of textual errors. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:29:45 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 7890-3:1988 (E) BSI 06-19993 6.3.3 Spectrometric measurements Measure the absorbance
40、of the solution at 415 nm in cells of optical path length 40 mm or 50 mm against distilled water as a reference. Let the absorbance measured be As units. NOTETests have indicated that the absorbance of the coloured solutions remains constant for at least 24 h. 6.3.4 Plotting the calibration graph Su
41、btract the absorbance of the blank solution from the absorbances of each of the calibration solutions and plot a calibration graph of absorbance against mass of nitrate3), m(N) g. Check that the graph is linear and passes through the origin. If it is not, repeat the calibration. 6.4 Determination Pi
42、pette the selected test portion (6.1), of volume V ml such that the aliquot contains a mass of nitrate nitrogen of between m(N) = 1 g and 5 g, into a small evaporating dish (4.2). Then proceed as in 6.3.2 and 6.3.3. 6.5 Correction for test portion absorption If absorption by the test portion at the
43、analytical wavelength is known, or suspected, to interfere (as may arise with highly coloured samples), carry out the operations given in 6.3.2 and 6.3.3 on the duplicate test portion but omitting the addition of sodium salicylate solution. Let the absorbance measured be At units. 7 Expression of re
44、sults 7.1 Method of calculation Calculate the absorbance due to nitrate3) in the test portion, Ar, from the equation Ar= As Ab or, when a correction for sample absorption has been made, from the equation Ar= As Ab At In both equations, As, Ab and At refer to the sample, blank and correction absorban
45、ces respectively (see 6.2, 6.3.3 and 6.5). Read off from the calibration graph (6.3.4) the mass of nitrate, m(N), in micrograms corresponding to the absorbance value Ar. The nitrate content in the sample, AN, in milligrams per litre, is given by the formula where V is the volume of the test portion,
46、 in millilitres. Table 1 Conversion table Example: = 1 mg/l corresponds to AN = 0,226 mg/l. 7.2 Repeatability and reproducibility4) Standard deviations of repeatability and reproducibility are shown in Table 2. 8 Test report The test report shall include the following information: a) a reference to
47、this part of ISO 7890; b) precise identification of the sample; c) details of the storage of the laboratory sample before analysis; d) a statement of the repeatability achieved by the laboratory when using this method; e) the result, expressed as AN in milligrams per litre, or as in milligrams per l
48、itre or as c(NO3) in millimoles per litre; f) any deviation from the standard procedure or any other circumstances that may have affected the result. 3) See national foreword for details of textual errors. mN() V - Nitratea c(NO3)A AN mmol/lmg/lmg/l c(NO3) = 1 mmol/l = 1 mg/l AN = 1 mg/l 1 0,016 1 0
49、,071 4 62 1 4,427 14,01 0,226 1 a See national foreword for details of textual errors. 4) Information derived from a United Kingdom interlaboratory test involving four participants. ANO 3 ANO 3 ANO 3 ANO 3 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:29:45 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 7890-3:1988 (E) 4 BSI 06-1999 Table 2 Standard deviation of repeatability and reproducibility Sample Nitrateb content A AN Test portion volumeStandard deviat