1、BRITISH STANDARD BS 6068-2.9: 1984 ISO 6059:1984 Water quality Part 2: Physical, chemical and biochemical methods Section 2.9 Determination of the sum of calcium and magnesium: EDTA titrimetric method ISO title: Water quality Determination of the sum of calcium and magnesium EDTA titrimetric method
2、UDC 556:614.777:628.1/.3:663.63:543.24:546.41+546.46BS6068-2.9:1984 This British Standard, having been prepared under the directionof the Environment and Pollution Standards Committee, was published under the authorityof the Board of BSI andcomes into effect on 31December1984 BSI 10-1999 The followi
3、ng BSI references relate to the work on this standard: Committee reference EPC/44 Draft for comment 83/50598 DC ISBN 0 580 14199 3 Amendments issued since publication Amd. No. Date of issue CommentsBS6068-2.9:1984 BSI 10-1999 i Contents Page National foreword ii 1 Scope and field of application 1 2
4、References 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Sampling and samples 2 7 Procedure 2 8 Expression of results 2 9 Precision 3 10 Interferences 3 11 Test report 3 Annex A Concepts of hardness of water 4 Bibliography 4 Publications referred to Inside back coverBS6068-2.9:1984 ii BSI 10-1999 Nat
5、ional foreword This Section of this British Standard, which has been prepared under the direction of the Environment and Pollution Standards Committee, is identical with ISO6059:1984 “Water quality Determination of the sum of calcium and magnesium EDTA titrimetric method”. The International Standard
6、 was prepared by subcommittee2, Physical, chemical and biochemical methods, of TechnicalCommittee147, Water quality, of the International Organization for Standardization (ISO) as a result of discussion in which the UK participated. This British Standard is being published in a series of Parts subdi
7、vided into Sections that will generally correspond to particular International Standards. Sections are being, or will be, published in Parts1 to6 which, together with Part0, are as follows. Part 0: Introduction; Part 1: Glossary; Part 2: Physical, chemical and biochemical methods; Part 3: Radiologic
8、al methods; Part 4: Microbiological methods; Part 5: Biological methods; Part 6: Sampling. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not ident
9、ical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring
10、 to this standard, they should be read as “British Standard”. It is current practice in British Standards for the symbol “L” to be used for litre rather than“l” and for the term “sulphur” to be used rather than “sulfur”. The following ISO standard (at present in course of preparation), which is refe
11、rred to in clause 2, is essentially of an advisory nature and the absence of corresponding British Standards does not affect the validity of this standard. However, it is intended that this International Standard will be published as a Section of this British Standard and the anticipated title has b
12、een included for information only. The Technical Committee has reviewed the provisions of ISO385-1 (at present in the course of preparation) to which reference is made in clauses2 and5, and has decided that burettes specified to BS846:1980,25mL nominal capacity, smallest scale interval0.05mL, ClassA
13、, are suitable. Cross-references International Standards Corresponding British Standards ISO 5667 BS 6068 Water quality: Part 6: Sampling Part 1:1980 Section 6.1:1981 Guidance on the design of sampling programmes (Identical) Part 2:1982 Section 6.2:1983 Guidance on sampling techniques (Identical) In
14、ternational Standard Corresponding British Standard ISO 5667-3 BS 6068 Water quality Section 6.3 Guidance on the preservation and handling of samplesBS6068-2.9:1984 BSI 10-1999 iii Textual error. When adopting the text of the International Standard the textual error given below was discovered. It ha
15、s been marked in the text and has been reported toISO in a proposal to amend the text of the International Standard. In clause7.2.1, paragraph 2, line4, “dropwise” should be inserted after “solution”. Additional information. In the Annex A,A.2.2 refers to the UK hardness degree(Clark). This is now a
16、lmost obsolete and in the UK hardness is now usually recorded as milligrams of calcium carbonate per litre, or, less preferred, as parts per million (ppm) of calcium carbonate. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are r
17、esponsible 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 toiv, pages1to4, an inside back cover and a back cover. This standard has been
18、 updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS6068-2.9:1984 BSI 10-1999 1 1 Scope and field of application This International Standard specifies a titrimetric method using ethylenediaminetetra
19、acetic acid (EDTA) for the determination of the sum of the calcium and magnesium concentrations in ground waters, surface waters and drinking waters. The method is not intended for effluents and waters having a high concentration of salts, such as sea waters. The lowest concentration that can be det
20、ermined is0,05mmol/l. 2 References ISO 385-1, Laboratory glassware Burettes Part1: General requirements 1) . ISO 5667, Water quality Sampling Part1:Guidance on the design of sampling programmes Part 2: Guidance on sampling techniques Part 3: Guidance on the preservation and handling of samples 2) .
21、3 Principle Complexometric titration of calcium and magnesium with an aqueous solution of the disodium salt of EDTA at apH value of10. Mordant black11, which forms a claret or violet colour in the presence of calcium and magnesium ions, is used as the indicator. In the titration, the EDTA, reacts fi
22、rst with the free calcium and magnesium ions in solution, and then, at the equivalence point, with those calcium and magnesium ions which are combined with the indicator, liberating the indicator and causing the colour to change from claret or violet to blue. The results are given in amount of subst
23、ance concentration units. If the calcium content has been determined separately, the mass concentration of magnesium can be computed. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Buffer solution Dissolve
24、67,5g of ammonium chloride (NH 4 Cl) in570ml of ammonia solution 25%(m/m); 20 =0,910g/ml. Then add5,0g of the disodium magnesium salt of EDTA (C 10 H 12 N 2 O 8 Na 2 Mg) and dilute to1000ml with water. Store the solution (shelf-life limited) in a polyethylene bottle. Dilute10ml of the solution to100
25、ml with water. If this solution fails to give apH value of10 0,1, discard the original solution. 4.2 EDTA, standard volumetric solution, c(Na 2 EDTA) . 10mmol/l. 4.2.1 Preparation Dry a portion of the disodium salt of EDTA dihydrate (C 10 H 14 N 2 O 8 Na 2 2H 2 O) at80 C for2h, dissolve3,725g of the
26、 dry salt in water and dilute to1000ml in a volumetric flask. Store the EDTA solution in a polyethylene bottle and check the concentration at regular intervals. 4.2.2 Standardization Standardize the solution (4.2.1) against the calcium standard reference solution (4.3) by the procedure described in
27、clause7. Use 20,0ml of the calcium standard reference solution (4.3) and dilute to50ml. 4.2.3 Calculation of the concentration The concentration of the EDTA solution, c 1 , expressed in millimoles per litre, is given by the equation where 4.3 Calcium, standard reference solution, c(CaCO 3 )=10mmol/l
28、. Dry a sample of pure calcium carbonate for2h at150 C, and allow to cool to room temperature in a desiccator. 1) At present at the stage of draft. (Partial revision of ISO/R 385-1964.) 2) At present at the stage of draft. c 2 is the concentration, expressed in millimoles per litre, of the calcium s
29、tandard reference solution (4.3); V 1 is the volume, in millilitres, of the calcium standard reference solution; V 2 is the volume, in millilitres, of the EDTA solution used for the standardization. c 1 c 2V 1 V 2 - =BS6068-2.9:1984 2 BSI 10-1999 Place1,001g in a500ml conical flask, and moisten it w
30、ith water. Add dropwise4mol/l hydrochloric acid until all the carbonate has dissolved. Avoid adding excess acid. Add200ml of water and boil for a few minutes to expel carbon dioxide. Cool to room temperature and add a few drops of methyl red indicator solution. Add3mol/l ammonia solution until the s
31、olution turns orange. Transfer the solution quantitatively to a1000ml one-mark volumetric flask and make up to the mark with water. 1ml of the solution contains 0,4008mg(0,01mmol) of calcium. NOTECommercially available solutions may be used. 4.4 Mordant black 11, indicator. Dissolve 0,5g of mordant
32、black11, the sodium salt of 1-(1-hydroxy-2-naphthylazo)-6-nitro-2- naphthol-4-sulfonicacid (C 20 H 12 N 3 O 7 SNa), in100ml of triethanolamine (HOCH 2 CH 2 ) 3 N. Up to25ml ethanol may be added instead of triethanolamine to reduce the viscosity of the solution. NOTETo facilitate the detection of the
33、 end-point, the indicatormay be modified by the addition of0,17g methanil salt(4-anilido-azobenzene-sulfonic acid sodium salt). The colour will now change from red to pale grey or green. 5 Apparatus Ordinary laboratory apparatus, and: Burette, 25ml capacity, graduated in divisions of0,05ml, conformi
34、ng to the requirements of ISO385-1, class A, or equivalent equipment. 6 Sampling and samples The samples should be taken in accordance with the relevant parts of ISO5667. 7 Procedure 7.1 Preparation of the test portion The samples do not require pretreatment except that samples containing gross amou
35、nts of particulate matter should be filtered through a0,454m pore size filter as soon as possible after collection. If filtration is carried out there is a risk of removing some calcium and magnesium. Dilute test portions having a total calcium and magnesium content exceeding3,6mmol/l until they are
36、 below that concentration and record the dilution factorF. If the test portions have been acidified for preservation, neutralize them with the calculated amounts of2mol/l sodium hydroxide solution. In the calculation of results, take into account any dilution of the sample, or test portion, by acid
37、or alkali. 7.2 Determination 7.2.1 By means of a pipette, transfer50,0ml of the test solution to a250ml conical flask. Add4ml of the buffer solution (4.1) and3 drops of mordant black11 indicator (4.4). The colour of solution should now turn to claret or violet and itspH value should be10,0 0,1. Titr
38、ate immediately, adding the EDTA solution(4.2) from a burette (clause5) under continuous stirring. Titrate rather rapidly at the beginning and slowly towards the end of the titration. Add the EDTA solution when the colour of the solution 3)starts to change from claret or violet to blue. The end-poin
39、t is reached when the last red shade has disappeared. The colour should not change any more on addition of another drop of EDTA solution. 7.2.2 Titrate an additional test portion in the following manner. Transfer50,0ml of the test solution to a flask. Add an amount of EDTA solution that is0,5ml less
40、 than that consumed in the first titration (7.2.1). Add4ml of the buffer solution (4.1) and3drops of the mordant black11indicator (4.4). Add EDTA dropwise until the end-point is reached. 7.2.3 If the consumption of EDTA solution is less than4,5ml, titrate using a larger test portion, and increase th
41、e volume of the buffer solution (4.1) in proportion. If the consumption of EDTA solution exceeds20ml, titrate using a smaller test portion. Add water so that the starting volume is50ml. 8 Expression of results The sum of the calcium and magnesium contents, c Ca+Mg , expressed in millimoles per litre
42、, is given by the equation where 3) See national foreword for details of textual error. c 1 is the concentration, expressed in millimoles per litre, of the EDTA solution; V 0 is the volume, in millilitres, of the test portion (normally50ml); V 3 is the volume, in millilitres, of EDTA used in the tit
43、ration (see7.2.2). c CaMg + c 1V 3 V 0 - =BS6068-2.9:1984 BSI 10-1999 3 If a diluted test portion has been used, modify the calculation accordingly, using the dilution factorF. For calculation of hardness, see theAnnex A. 9 Precision The repeatability of the procedure is 0,04mmol/l, corresponding to
44、 approximately2drops of the EDTA solution. 10 Interferences WARNING Sodium cyanide is a poison. Take the necessary precautions when handling and disposing of the chemical. Solutions containing sodium cyanide must not be acidified. The metal ions of aluminium, barium, lead, iron, cobalt, copper, mang
45、anese, tin and zinc interfere with the determination, either because they are titrated as calcium and magnesium, or because they obscure the colour change at the end-point. Orthophosphate and carbonate ions may precipitate calcium at thepH of the titration. Also some organic matter may interfere wit
46、h the determination. The interference from iron ions at concentrations of10mg/l or less can be masked by the addition of250mg of sodium cyanide to the test portion. Cyanide also minimizes interference from zinc, copper and cobalt. Ensure that the solution is alkaline before adding sodium cyanide. If
47、 the interferences cannot be eliminated, use an atomic absorption method. A suitable method will form the subject of a future International Standard. 11 Test report The test report shall include the following information: a) a reference to this International Standard; b) complete identification of t
48、he sample; c) the result, expressed in millimoles per litre, to the nearest0,02mmol/l; d) the preparation of the test portion (if any); e) any deviation from the procedure specified in this International Standard or any other circumstances that may have affected the results.BS6068-2.9:1984 4 BSI 10-
49、1999 Annex A Concepts of hardness of water (This annex does not form part of the Standard.) A.0 Introduction Hardness of water is an old concept used to describe the content of calcium and magnesium in waters. There are different kinds of hardness (total hardness, carbonate hardness and others) and various countries have adopted different definitions of the concept. Some definitions are given in clauseA.1 as examples. A.1 Definitions A.1.1 total hardness: The total concentration of calcium
