1、BRITISH STANDARD BS6068-2.47: 1995 ISO11083: 1994 Water quality Part 2: Physical, chemical and biochemical methods Section 2.47 Determination of chromium (VI) Spectrometric method using 1,5-diphenylcarbazideBS 6068-2.47:1995 This British Standard, having been prepared under the directionof the Healt
2、h and Environment Sector Board, waspublished under the authorityof the Standards Boardand comes intoeffecton 15 April1995 BSI07-1999 The following BSI references relate to the work on this standard: Committee referenceEPC/44 Draft for comment92/54770DC ISBN 0 580 24117 3 Committees responsible for t
3、his British Standard The preparation of this British Standard was entrusted to Technical CommitteeEPC/44, Water quality, upon which the following bodies were represented: Association of Consulting Scientists British Association for Chemical Specialities British Gas plc Chemical Industries Associatio
4、n Convention of Scottish Local Authorities Department of Economic Development (Northern Ireland) Department of the Environment for Northern Ireland Department of the Environment (Water Directorate) Department of Trade and Industry (Laboratory of the Government Chemist) Electricity Association Indust
5、rial Water Society Institution of Gas Engineers Institution of Water and Environmental Management Institution of Water Officers National Rivers Authority Royal Institute of Public Health and Hygiene Royal Society of Chemistry Scottish Association of Directors of Water and Sewerage Services Soap and
6、Detergent Industry Association Society of Chemical Industry Water Companies Association Water Research Centre Water Services Association of England and Wales Amendments issued since publication Amd. No. Date CommentsBS6068-2.47:1995 BSI 07-1999 i Contents Page Committees responsible Inside front cov
7、er National foreword ii 1 Scope 1 2 Principle 1 3 Reagents 1 4 Apparatus 1 5 Sampling and sample pretreatment 1 6 Interferences 2 7 Procedure 2 8 Expression of results 3 9 Test report 4 Table 1 Precision data 4BS 6068-2.47:1995 ii BSI 07-1999 National foreword This Section of BS6068 has been prepare
8、d by Technical CommitteeEPC/44, Water quality, and is identical with ISO11083:1994 Water quality Determination of chromium (VI) Spectrometric method using1,5-diphenylcarbazide, published by the International Organization for Standardization. The international standard was prepared by ISO Technical C
9、ommittee147, Water quality, with the active participation and approval of the UK BS6068 is being published in a series of Parts subdivided into Sections that will generally correspond to particular international standards. Sections are being, or will be, published in Parts1 to7, which, together with
10、 Part0, are as follows. 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: Sampling; Part 7: Precision and accuracy. It has been assumed in the drafting of this
11、 Section of BS6068 that the execution of its provisions is entrusted to appropriately qualified and experienced people. Standard chemical procedures should be followed throughout. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards ar
12、e 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, pagesi andii, pages1 to4 and a back cover. This standard has been updated (see cop
13、yright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.ISO11083:1994(E) BSI 07-1999 1 1 Scope This International Standard specifies a spectrometric method for determination of chromium(VI) in water. The method is applicable to t
14、he determination of dissolved chromium(VI) in waters in the concentration range of0,05mg/l to3mg/l. The application range may be extended by dilution of the sample. 2 Principle After sample pretreatment (which aims at stabilizing the valency states of chromium(VI) and chromium(III), if present) chro
15、mium(VI) reacts with1,5-diphenylcarbazide to form a red-violet chromium-1,5-diphenylcarbazone complex. The absorbance of this complex is then measured at a wavelength between540nm and550nm, the exact wavelength being given in the test report. 3 Reagents Use only reagents of recognized analytical gra
16、de and only distilled water or water of equivalent purity. Commercially available reagents with guaranteed concentrations may also be used. 3.1 Phosphate buffer solution, pH=9,0 0,2. Dissolve456g of dipotassium hydrogen phosphate (K 2 HPO 4 .3H 2 O) in1000ml of water. Check the pH and adjust if nece
17、ssary. 3.2 Sodium hydroxide solution Dissolve20g of sodium hydroxide (NaOH) in100ml of water. 3.3 Phosphoric acid solution A Dilute10ml of phosphoric acid (H 3 PO 4 , =1,71g/ml) to100ml with water. 3.4 Phosphoric acid solution B Dilute700ml of phosphoric acid (H 3 PO 4 , =1,71g/ml) to1000ml with wat
18、er. 3.5 Aluminium sulfate solution Dissolve247g of aluminium sulfate Al 2 (SO 4 ) 3 .18H 2 O in1000ml of water. 3.6 Sulfite solution Dissolve11,8g of sodium sulfite (Na 2 SO 3 ) in water and dilute to100ml. This solution is stable for about a week. 3.7 Sulfite test paper 3.8 1,5-diphenylcarbazide so
19、lution Dissolve1g of1,5-diphenylcarbazide (C 13 H 14 N 4 O) in100ml of propanone (acetone), C 3 H 6 O, and acidify with one drop of glacial acetic acid. Stored in a brown glass bottle in a refrigerator at4C, this solution is stable for two weeks. Discard the solution if it becomes discoloured. 3.9 S
20、odium hypochlorite solution Dilute70ml of sodium hypochlorite solution (NaOCl, approximately150g of free Cl 2per litre) with water to1000ml. Stored in a brown glass bottle in a refrigerator at4C, this solution is stable for one week. 3.10 Potassium iodide starch test paper 3.11 Chromium(VI) stock so
21、lution WARNING Potassium chromate may be carcinogenic. Dissolve2,829g of potassium dichromate (K 2 Cr 2 O 7 ) in water in a1000ml volumetric flask and dilute to volume. This solution is stable indefinitely. 1ml of this solution contains1mg ofCr. 3.12 Chromium(VI) standard solution Transfer5ml of the
22、 chromium(VI) stock solution(3.11) to a1000ml volumetric flask and dilute to volume with water. Prepare this solution on the day of use. 1ml of this solution contains54g of Cr. 3.13 Sodium chloride, NaCl 4 Apparatus Ordinary laboratory apparatus and 4.1 Photometer or spectrometer, equipped with cell
23、s of optical path lengths between10mm and50mm. 4.2 Membrane filtration device, equipped with membrane filters with a pore size of0,44m to0,454m. 4.3 pH-measuring equipment 4.4 Gas flow control 5 Sampling and sample pretreatment Perform these pretreatment steps immediately after sample collection. An
24、alyse the samples as soon as possible after collection. NOTE 1If in doubt as to which procedure to use, take two samples and treat them according to either5.1 and7.1, or5.2 and7.2. If the results do not differ significantly, the procedures described in5.1 and7.1 may be used. 5.1 Samples in the absen
25、ce of oxidizing or reducing substances Collect a1000ml sample in a glass bottle, add10ml of buffer solution(3.1) and mix. Measure the pH using the equipment(4.3); it shall be between7,5 and8,0.ISO 11083:1994(E) 2 BSI 07-1999 If the pH is outside this range, adjust with sodium hydroxide solution(3.2)
26、 or phosphoric acid solution A(3.3), accordingly. Add1ml of aluminium sulfate solution(3.5) and mix. Check the pH; it shall be between7,0 and7,2. If the pH is outside this range, adjust with phosphoric acid solution A(3.3). Allow the precipitate to settle for at least2h. Decant the supernatant and f
27、ilter200ml through a membrane filter(4.2), discarding the first50ml of filtrate. 5.2 Samples in the presence of oxidizing or reducing substances Collect a1000ml sample in a glass bottle, add10ml of buffer solution(3.1) and mix. Measure the pH using the equipment(4.3); it shall be between7,5 and8,0.
28、If the pH is outside this range, adjust with sodium hydroxide solution(3.2) or phosphoric acid solution A(3.3), accordingly. Add1ml of aluminium sulfate solution(3.5) and mix. Check the pH; it shall be between7,0 and7,2. If the pH is outside this range, adjust with phosphoric acid solution A(3.3). A
29、dd1ml of sulfite solution(3.6), checking for an excess of sulfite using sulfite test paper(3.7). If there is no excess of sulfite, add more sulfite solution until an excess is obtained. Allow the precipitate to settle for at least2h. Decant the supernatant and filter200ml through a membrane filter(4
30、.2), discarding the first50ml of filtrate. 6 Interferences In the presence of lead, barium and silver ions (salts), chromates of low solubility may be formed and the chromium(VI) contained in them will not be determined. Hexavalent molybdenum and mercury salts also form a yellow or blue colour respe
31、ctively with the reagent, but the intensities are much lower than for chromium(VI). Iron(III) forms a yellow colour at concentrations above1mg/l and vanadium forms a yellow colour that fades. Chromium(III) and other interfering metal ions are precipitated in a phosphate-buffered solution using alumi
32、nium sulfate as a precipitation aid and are removed by filtration. Valency changes of chromium due to the presence of oxidizing or reducing substances can be avoided by using the following pretreatment steps. Oxidizing substances are reduced by the addition of sulfite to the neutralized sample; chro
33、mium(VI) will not react under these conditions. Excess sulfite and other reducing substances are then oxidized with hypochlorite. Excess hypochlorite and any chloroamines formed are destroyed in the acid solution by the addition of sodium chloride and the chlorine formed is purged with air. In spite
34、 of this pretreatment of the sample, slow reduction of chromium(VI) may occur in some waters. Leachate from landfills, raw domestic waste water and certain waste waters from chemical plants will show losses of chromium(VI) after several hours. It is therefore essential that these samples be analysed
35、 as soon as possible after collection. Ammonia nitrogen does not interfere in concentrations below500mg/l, but amine compounds may be transformed by hypochlorite into chloroamines, which are not always decomposed by the addition of chloride. This interference is indicated by the appearance of a yell
36、ow or brownish colour on addition of1,5-diphenylcarbazide. Nitrite nitrogen interferes with the formation of the red violet chromium(VI)-1,5-diphenylcarbazone complex in concentrations exceeding20mg/l. Vanadium in excess of4mg/l, and molybdenum and mercury each in excess of200mg/l may interfere. 7 P
37、rocedure 7.1 Procedure in the absence of oxidizing or reducing substances Transfer50ml (volume V) of the filtrate(5.1) to a100ml volumetric flask. Add2ml of phosphoric acid solution B(3.4) and2ml of diphenylcarbazide solution(3.8) and dilute to100ml with water. Measure the absorbance after5min to15m
38、in at a wavelength between540nm and550nm using water in the reference cell (absorbance A s ), and cells with an optical path length of40mm or50mm for concentrations below0,5mg/l, and of10mm for concentrations between0,5mg/l and3mg/l. If the concentration is higher than3mg/l, repeat the determination
39、, using a smaller aliquot of the filtrate (volume V). For the blank value, carry out a blank test in parallel with the determination using water in place of the sample (absorbance A b ). NOTE 2This blank does not take into account the chromium content of the precipitation reagents, which has been fo
40、und to be negligible. If the measured blank disagrees significantly with the blank from the calibration function(7.3), check the latter.ISO11083:1994(E) BSI 07-1999 3 If the filtrate is coloured or turbid, take another aliquot and treat it as described in this subclause, omitting the1,5-diphenylcarb
41、azide solution. Use the absorbance measured as a colour correction (absorbance A t ). 7.2 Procedure in the presence of oxidizing or reducing substances Transfer50ml (volume V) of the filtrate(5.2) to a100ml volumetric flask. Add1ml of sodium hypochlorite solution(3.9), after checking for1min for exc
42、ess chlorine using the potassium iodide starch test paper(3.10). If there is no excess chlorine, add more sodium hypochlorite solution(3.9) until an excess is obtained. Add2ml of phosphoric acid solution B(3.4), dissolve10g of sodium chloride(3.13) in the sample, and pass air through the sample with
43、 a flow rate of approximately40l/h for40min. Perform this procedure in a fume chamber. Add2ml of1,5-diphenylcarbazide solution(3.8) and dilute to100ml with water. Measure the absorbance after5min to15min at a wavelength between540nm and550nm using water in the reference cell (absorbance A s ) and ce
44、lls with an optical path length of40mm or50mm for concentrations below0,5mg/l, and of10mm for concentrations between0,5mg/l and3mg/l. If the concentration is higher than3mg/l, repeat the determination, using a smaller aliquot of the filtrate (volume V). For the blank value, repeat the procedure, usi
45、ng water in place of the filtrate (absorbance A b ). NOTE 3This blank does not take into account the chromium content of the precipitation reagents, which has been found to be negligible. If the measured blank disagrees significantly with the blank from the calibration function(7.3), check the latte
46、r. If the filtrate is coloured or turbid, take another aliquot and treat it as described in this subclause, omitting the1,5-diphenylcarbazide solution. Use the absorbance measured as colour correction (absorbance A t ). 7.3 Calibration Pipette, for example, 0ml; 0,5ml; 1,0ml; 2,0ml; 3,0ml; 4,0ml and
47、5,0ml of chromium(VI) standard solution(3.12) into a series of100ml volumetric flasks. Dilute each to approximately40ml with water, add2ml of phosphoric acid solution B(3.4) and2ml of1,5-diphenylcarbazide solution(3.8) and dilute to100ml with water. These calibration solutions have concentrations of
48、0mg/l;0,025mg/l;0,05mg/l;0,10mg/l; 0,15mg/l;0,20mg/l and0,25mg/l of chromium(VI) respectively. Measure the absorbance after5min to15min at a wavelength between540nm and550nm (absorbance A c ) in cells with an optical path length of40mm or50mm using water in the reference cell. The wavelength used sh
49、all be the same for the calibration and the measurement. Plot the mass concentration of chromium(VI) against the absorbance values to establish the calibration graph. Alternatively, calculate the calibration graph by regression analysis. The slope of the calibration graph is a measure of the sensitivity of the method. The ordinate intercept is the blank. Check both the slope of the graph and the blank regularly, especially when new batches of reagents are used. For calibration of other concentration ranges, proceed in the same way using differen
