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+663.63:53/54BS6068-2.36:1989 This British Standard, having b
2、een prepared under the directionof the Environment andPollution Standards PolicyCommittee, was publishedunderthe authority ofthe BoardofBSI and comesintoeffecton 29September1989 BSI 06-1999 The following BSI references relate to the work on this standard: Committee reference EPC/44 Draft for comment
3、 87/51929 DC ISBN 0 580 17681 9 Amendments issued since publication Amd. No. Date of issue CommentsBS6068-2.36:1989 BSI 06-1999 i Contents Page National foreword ii 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 Ann
4、ex A (normative) The effect of other substances on this method Inside back cover Table 1 Conversion table 3 Table 2 Standard deviation of repeatability and reproducibility 4BS6068-2.36:1989 ii BSI 06-1999 National foreword This Section of BS6068, which has been prepared under the direction of the En
5、vironment and Pollution Standards Policy Committee, is identical with ISO7890-3:1988 “Water quality Determination of nitrate Part3:Spectrometric method using sulfosalicylic acid”. The international standard was prepared by subcommittee2, Physical, chemical and biochemical methods, of Technical Commi
6、ttee147, 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 BS6068 should only be carried out in laboratories with suitable facilities and by suitably qualified persons with an ap
7、propriate 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 generally correspond to particular international stand
8、ards. Sections are being, or will be, published in Parts1 to7, which together with Part0, are listed below. Part 0: Introduction; Part 1: Glossary; Part 2: Physical, chemical and biochemical methods; Part 3: Radiological methods; Part 4: Microbiological methods; Part 5: Biological methods; Part 6: S
9、ampling; 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 the text of the international standard. In clauses 3.6
10、, 3.7, 3.8, 6.1, 6.3.1, 6.3.4, 7.1 andTable 2, “nitrate” should be read as “nitrate nitrogen”. In clause7.1 insert the following for the final paragraph (and beforeTable 1): SeeTable 1 for conversion of A Nto in milligrams per litre or c (NO 3 ) in millimoles per litre. A British Standard does not p
11、urport 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. A NO 3 Summary of pages This document comprises a front cover, an insi
12、de front cover, pagesi andii, pages1 to4, 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.ISO7890-3:1988(E) BSI 06-1999 1 1 Scope 1.1 Substance
13、 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 suitable for application to raw and potable water samples. 1.3 Range Up to a nitrate nitrogen concentration, A N of0,2mg/l using the maximum test portion volume of 25
14、ml. The range can be extended upwards by taking smaller test portions. 1.4 Limit of detection 1) Using cells of optical path length40 mm and a25 ml test portion volume the limit of detection lies within the range A N =0,003 to0,013 mg/l. 1.5 Sensitivity 1) A nitrate nitrogen concentration of A N=0,2
15、 mg/l gives an absorbance of about0,68 unit, using a25ml test portion and cells of optical path length40 mm. 1.6 Interferences A range of substances often encountered in water samples has been tested for possible interference with this method. Full details are given inAnnex A. The main potential int
16、erferents are chloride, orthophosphate, magnesium and manganese(II), as shown inAnnex A. Other tests have shown that this method will tolerate a sample colour of up to150 mg/l Pt providing the test portion absorption correction procedure is followed. (See6.5.) 2 Principle Spectrometric measurement o
17、f the yellow compound formed by reaction of sulfosalicylic acid (formed by addition to the sample of sodium salicylate and sulfuric acid) with nitrate and subsequent treatment with alkali. Disodium dihydrogen ethylenedinitrilotetraacetate (EDTANa 2 ) is added with the alkali to prevent precipitation
18、 of calcium and magnesium salts. Sodium azide is added to overcome interference from nitrite. 3 Reagents During the analysis, use only reagents of recognized analytical grade, and only distilled water or water of equivalent purity. 3.1 Sulfuric acid, c(H 2SO 4 ) . 18 mol/l, A=1,84 g/ml. WARNING When
19、 using this reagent, eye protection and protective clothing are essential. 3.2 Glacial acetic acid, c(CH 3 COOH). 17 mol/l, A=1,05 g/ml. WARNING When using this reagent, eye protection and protective clothing are essential. 3.3 Alkali solution, A NaOH=200 g/l,= 50 g/l. Cautiously dissolve200 g 2 g o
20、f sodium hydroxide pellets in about800 ml of water. Add50 g0,5 g of disodium dihydrogen ethylenedinitrilotetraacetate dihydrate (EDTANa 2 ) CH 2 -N(CH 2 COOH)CH 2 -COONa 2 .2H 2 O and dissolve. Cool to room temperature and make up to1 litre with water in a measuring cylinder. Store in a polyethylene
21、 bottle. This reagent is stable indefinitely. WARNING When using this reagent, eye protection and protective clothing are essential. 3.4 Sodium azide solution, =0,5 g/l. Carefully dissolve0,05 g0,005 g of sodium azide in about90 ml of water and dilute to100 ml with water in a measuring cylinder. Sto
22、re in a glass bottle. This reagent is stable indefinitely. WARNING This reagent is very toxic if swallowed. Contact between the 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 solu
23、tion, =10 g/l. Dissolve 1 g0,1 g of sodium salicylate (HO-C 6 H 4 -COONa) in100 ml1 ml of water. Store in a glass or polyethylene bottle. Prepare this solution freshly on each day of operation. 1) Information derived from a United Kingdom interlaboratory test involving four participants. Limit of de
24、tection was taken as4,65 times the within- batch standard deviation of the blank. A CH 2 -NCH 2 COOH ()CH 2 -COONa 2 .2H 2 O A NaN 3 A NH 2 .SO 3 H A HO-C 6 H 4 -COONaISO7890-3:1988(E) 2 BSI 06-1999 3.6 Nitrate 2) , stock standard solution, A N=1000 mg/l. Dissolve 7,215 g0,001 g of potassium nitrate
25、 (KNO 3 ) (previously dried at105C for at least2 h) in about750 ml of water. Quantitatively transfer to a1 litre one-mark volumetric flask and make up to volume with water. Store the solution in a glass bottle for not more than2 months. 3.7 Nitrate 2) , standard solution, A N=100 mg/l. Pipette 50 ml
26、 of the stock standard solution (3.6) into a500 ml one-mark volumetric flask and make up to the mark with water. Store the solution in a glass bottle for not more than1 month. 3.8 Nitrate 2) , working standard solution, A N=1 mg/l. Into a 500 ml one-mark volumetric flask, pipette5ml of standard nitr
27、ate solution (3.7). Make up 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 of415 mm and equipped with cells of optical path length40 mm or50 mm. 4.2 Evaporating dishes, abo
28、ut50 ml capacity. If the 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 of6.3.2 to clean them. 4.3 Water bath, boiling, capable of accepting at least six of the evaporating dishes (4.2). 4.4 Water ba
29、th, capable of thermostatic regulation to25C0,5C. 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 between2C and5C may preserve many types of sample, but checks should be made to confirm
30、this with each 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 port
31、ion The maximum test portion volume which can be used for the determination of nitrate 2)concentration up to A N=0,2 mg/l is25 ml. Use smaller test portions as appropriate in order to accommodate higher nitrate concentrations. Before taking the test portion, allow laboratory samples containing suspe
32、nded matter to settle, centrifuge them or filter them through a washed glass fibre filter paper. Neutralize samples having a pH value greater than8 with acetic acid (3.2) before taking the test portion. 6.2 Blank test Carry out a blank test in parallel with the determination, using5,00 ml0,05 ml of
33、water instead of the test portion. Let the absorbance measured be A bunits. 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 and5 ml respectively of the working standard nitrate 2)solution (3.8), correspo
34、nding to nitrate amounts of m(N) =1;2;3;4 and5 g in the respective dishes. 6.3.2 Colour development Add 0,5 ml0,005 ml of sodium azide solution (3.4), and0,2 ml0,002 ml of acetic acid (3.2). Wait for atleast5 min, and then evaporate the mixture to dryness in the boiling water bath (4.3). Add1ml0,01
35、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 ml0,01 ml of sulfuric acid (3.1) and dissolve the residue in the dish by gentle agitation. Allow the mixture to stand
36、for about10 min. Thenadd10ml0,1 ml of water followed by10ml0,1 ml of alkali solution (3.3). Quantitatively transfer the mixture to a25 ml one-mark volumetric flask, but do not make up to the mark. Place the flask in the water bath (4.4) at25C0,5C for10 min2 min. Then remove the flask and make up to
37、the mark with water. 2) Seenational foreword for details of textual errors.ISO7890-3:1988(E) BSI 06-1999 3 6.3.3 Spectrometric measurements Measure the absorbance of the solution at415 nm in cells of optical path length40 mm or50 mm against distilled water as a reference. Let the absorbance measured
38、 be A sunits. NOTETests have indicated that the absorbance of the coloured solutions remains constant for at least24 h. 6.3.4 Plotting the calibration graph Subtract the absorbance of the blank solution from the absorbances of each of the calibration solutions and plot a calibration graph of absorba
39、nce against mass of nitrate 3) , m(N)g. Check that the graph is linear and passes through the origin. If it is not, repeat the calibration. 6.4 Determination Pipette the selected test portion (6.1), of volume V ml such that the aliquot contains a mass of nitrate nitrogen of between m(N) =1g and5 g,
40、into a small evaporating dish (4.2). Then proceed as in6.3.2 and6.3.3. 6.5 Correction for test portion absorption If absorption by the test portion at the analytical wavelength is known, or suspected, to interfere (asmay arise with highly coloured samples), carry out the operations given in6.3.2 and
41、6.3.3 on the duplicate test portion but omitting the addition of sodium salicylate solution. Let the absorbance measured be A tunits. 7 Expression of results 7.1 Method of calculation Calculate the absorbance due to nitrate 3)in the test portion, A r , from the equation A r = A s A b or, when a corr
42、ection for sample absorption has been made, from the equation A r = A s A b A t In both equations, A s , A band A trefer to the sample, blank and correction absorbances respectively (see6.2, 6.3.3 and6.5). Read off from the calibration graph (6.3.4) the mass of nitrate, m(N), in micrograms correspon
43、ding to the absorbance value A r . The nitrate content in the sample, A N , in milligrams per litre, is given by the formula where V is the volume of the test portion, in millilitres. Table 1 Conversion table Example: = 1 mg/l corresponds to A N=0,226 mg/l. 7.2 Repeatability and reproducibility 4) S
44、tandard deviations of repeatability and reproducibility are shown inTable 2. 8 Test report The test report shall include the following information: a) a reference to this part of ISO7890; b) precise identification of the sample; c) details of the storage of the laboratory sample before analysis; d)
45、a statement of the repeatability achieved by the laboratory when using this method; e) the result, expressed as A Nin milligrams per litre, or as in milligrams per litre or as c(NO 3 ) in millimoles per litre; f) any deviation from the standard procedure or any other circumstances that may have affe
46、cted the result. 3) Seenational foreword for details of textual errors. m N () V - Nitrate a c(NO 3 ) A A N mmol/l mg/l mg/l c(NO 3 ) =1 mmol/l =1 mg/l A N=1 mg/l 1 0,0161 0,0714 62 1 4,427 14,01 0,226 1 a See national foreword for details of textual errors. 4) Information derived from a United King
47、dom interlaboratory test involving four participants. A NO 3 A NO 3 A NO 3 A NO 3ISO7890-3:1988(E) 4 BSI 06-1999 Table 2 Standard deviation of repeatability and reproducibility Sample Nitrate bcontent A A N Test portion volume Standard deviation aRepeatability A A N Reproducibility mg/l ml mg/l mg/l
48、 Standard solution (blank) Standard solution River water River water River water 0,00 0,20 4,40 9,18 10,0 25 25 1,0 0,5 0,5 0,001 to0,005 0,003 to0,011 0,07to0,22 0,13to0,54 0,06to0,09 0,005 to0,011 0,07to0,48 0,16to0,98 0,06to0,12 a The highest and lowest values from the exercise. All values have 9
49、 degrees of freedom. b See national foreword for details of textual errors.ISO7890-3:1988 (E) BSI 06-1999 Annex A (normative) The effect of other substances on this method 5) 5) Data from the United Kingdom. Other substance (expressed in terms of substance in brackets) Amount of other substance in a25 ml test portion Effect ing N of other substance in a25 ml test portion g m(N)= 0,00 g g m(N)= 5,00 g g Sodium chloride (Cl ) Sodium chloride (Cl ) Sodium hydrogen carbonate
