BS-6068-2.8-1984 ISO-6058-1984.pdf

BRITISH STANDARD BS 6068-2.8: 1984 ISO 6058:1984 Water quality Part 2: Physical, chemical and biochemical methods Section 2.8 Determination of calcium content: EDTA titrimetric method ISO title: Water quality Determination of calcium content EDTA titrimetric method UDC 556:614.777:628.1/.3:663.63:543.24:546.41 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 This British Standard, having been prepared under the direction of the Environment and Pollution Standards Committee, was published under the authority of the Board of BSI and comes into effect on 31 December 1984 © BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference EPC/44 Draft for comment 83/50597 DC ISBN 0 580 14198 5 Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 © BSI 10-1999i Contents Page National forewordii 1cope and field of application1 2References1 3Principle1 4Reagents1 5Apparatus2 6Sampling and samples2 7Procedure2 8Expression of results2 9Precision2 10Interferences2 11Test report3 Bibliography4 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 ii © BSI 10-1999 National foreword This Section of this British Standard, which has been prepared under the direction of the Environment and Pollution Standards Committee, is identical with ISO 6058:1984 “Water quality Determination of calcium content EDTA titrimetric method”. The International Standard was prepared by subcommittee 2, Physical, chemical and biochemical methods, of Technical Committee 147, 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 subdivided into Sections that will generally correspond to particular International Standards. Sections are being, or will be, published in Parts 1 to 6 which, together with Part 0, 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. 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 identical 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 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 referred 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 been included for information only. Cross-references International StandardsCorresponding British Standards ISO 5667 Part 1:1980 BS 6068 Water quality Part 6 Sampling Section 6.1:1981 Guidance on the design of sampling programmes (Identical) Part 2:1982Section 6.2:1983 Guidance on sampling techniques (Identical) International StandardCorresponding British Standard ISO 5667-3BS 6068 Water quality Section 6.3 Guidance on the preservation and handling of samples Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 © BSI 10-1999iii The Technical Committee has reviewed the provisions of ISO 385-1 (at present in the course of preparation) to which reference is made in clauses 2 and 5, and has decided that burettes specified to BS 846:1980, 25 mL nominal capacity, smallest scale interval 0.05 mL, Class A, are suitable. 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. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, 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 cover. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 © BSI 10-19991 1 Scope and field of application This International Standard specifies a titrimetric method using ethylenediaminetetraacetic acid (EDTA) for the determination of the calcium content of ground waters, surface waters and drinking waters. It can also be used for municipal and industrial raw waters, provided they do not contain interfering amounts of heavy metals. The method is not applicable to sea waters and other similar waters with a high concentration of salts. It is applicable to waters with calcium contents ranging from 2 to 100 mg/l (0,05 to 2,5 mmol/l). For waters containing more calcium than 100 mg/l, a diluted sample shall be used. 2 References ISO 385-1, Laboratory glassware Burettes Part 1: General requirements1). ISO 5667, Water quality Sampling Part 1: Guidance on the design of sampling programmes Part 2: Guidance on sampling techniques Part 3: Guidance on the preservation and handling of samples2). 3 Principle Complexometric titration of calcium ions with an aqueous solution of the disodium salt of EDTA at a pH value of between 12 and 13. HSN, which forms a red complex with calcium, is used as the indicator. Magnesium is precipitated as the hydroxide and does not interfere with the determination. In the titration, the EDTA first reacts with the free calcium ions and then with the calcium ions combined with the indicator. The indicator then changes its colour from red to bright blue. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Sodium hydroxide, 2 mol/l, solution. Dissolve 8 g of sodium hydroxide in 100 ml of freshly distilled water. Store in a polyethylene bottle. NOTETake precautions to avoid contamination by atmospheric carbon dioxide. 4.2 EDTA, standard volumetric solution, c(Na2EDTA) . 10 mmol/l. 4.2.1 Preparation Dry a portion of the disodium salt of EDTA dihydrate (C10H14N2O8Na2·2H2O) at 80 °C for 2 h, dissolve 3,725 g of the dry salt in water and dilute to 1 000 ml 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 clause 7. Use 20,0 ml of the calcium standard reference solution (4.3) and dilute to 50 ml. 4.2.3 Calculation of the concentration The concentration of the EDTA solution, c1, expressed in millimoles per litre, is given by the equation where c2 is the concentration, expressed in millimoles per litre, of the calcium standard reference solution (4.3); V1 is the volume, in millilitres, of the calcium standard reference solution; V2 is the volume, in millilitres, of the EDTA solution used for the standardization. 4.3 Calcium, standard reference solution, c(CaCO3) = 10 mmol/l. Dry a sample of pure calcium carbonate for 2 h at 150 °C, and allow to cool to room temperature in a desiccator. Place 1,001 g in a 500 ml conical flask, and moisten it with water. Add dropwise 4 mol/l hydrochloric acid until all the carbonate has dissolved. Avoid adding excess acid. Add 200 ml 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. Add 3 mol/l ammonia solution until the solution turns orange. Transfer the solution quantitatively to a 1 000 ml one-mark volumetric flask and make up to the mark with water. 1 ml of the solution contains 0,400 8 mg (0,01 mmol) of calcium. NOTECommercially available solutions may be used. 1) At present at the stage of draft. (Partial revision of ISO/R 385:1964.) 2) At present at the stage of draft. c1 c2V1 V2 -= Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 2 © BSI 10-1999 4.4 HSN, indicator. Mix thoroughly 0,2 g HSN 2-hydroxy-1 (2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid (C21H14N2O7S·3H2O) and 100 g of sodium chloride (NaCl). NOTEThis indicator is also known under the name “calcon carboxylic acid”. Another indicator that may be used for calcium is calcein 2,7-bis N, N-di-(carboxymethyl)-aminomethyl-fluorescein (C30H26N2O13). 5 Apparatus Ordinary laboratory apparatus, and: Burette, 25 ml capacity, graduated in divisions of 0,05 ml, conforming to the requirements of ISO 385-1, class A, or equivalent equipment. 6 Sampling and samples The samples should be taken in accordance with the relevant parts of ISO 5667. 7 Procedure 7.1 Preparation of the test portion The test portion should contain between 2 and 100 mg/l (0,05 and 2,5 mmol/l) of calcium. If a concentration in excess of 100 mg/l (2,5 mmol/l) is expected, dilute a known volume of test solution so as to bring the concentration within the required range and record the dilution factor F. If the test portions have been acidified for preservation, neutralize them with the calculated amounts of the sodium hydroxide solution (4.1). In the calculation of the results, take into account any dilution of the sample or test portion by acid or alkali. 7.2 Determination By means of a pipette, transfer 50,0 ml of the test solution to a 250 ml conical flask. Add 2 ml of the sodium hydroxide solution (4.1) and approximately 0,2 g of the HSN indicator (4.4). Mix and titrate immediately. Add the EDTA solution (4.2) from a burette (clause 5) under continuous stirring. Titrate rather rapidly at the beginning and slowly towards the end of the titration. The end-point is reached when the colour has changed to a distinct blue. The colour should not change any more on addition of another drop of EDTA solution. 8 Expression of results The calcium content, cCa, expressed in millimoles per litre, is given by the equation where c1 is the concentration, expressed in millimoles per litre, of the EDTA solution; V0 is the volume, in millilitres, of the test portion; V3 is the volume, in millilitres, of EDTA used in the titration. If required, the calcium content, ÕCa, expressed in milligrams per litre, is given by the equation where A is the relative atomic mass of calcium (40,08). If a diluted test portion has been used, modify the calculation accordingly, using the dilution factor F. 9 Precision Results obtained on the same test solution in different laboratories should agree within ± 5 mg/l in the range 30 to 100 mg/l. 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, manganese, tin and zinc interfere with the determination, either because they are titrated as calcium, or because they obscure the colour change at the end-point. Orthophosphate in concentrations greater than 1 mg/l precipitates calcium at the pH of the titration. Calcium carbonate may precipitate if the determination is performed too slowly or if the calcium content is high (above 100 mg/l or 2,5 mmol/l). cCa c1V3 V0 -= ÕCa c1V3 V0 -A×= Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 © BSI 10-19993 Interfering metal ions can be masked. The interference from iron at concentrations of 30 mg/l or less can be masked by the addition of either 250 mg of sodium cyanide or a few millilitres of triethanolamine to the sample just before the titration. Cyanide also minimizes interference from zinc, copper and cobalt, and triethanolamine reduces interference from aluminium. Ensure that the solution is alkaline before adding sodium cyanide. If 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 the sample; c) the result, expressed in milligrams per litre, to the nearest 1 mg/l, or in millimoles per litre, to the nearest 0,02 mmol/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. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 4 © BSI 10-1999 Bibliography 1 AMERICAN PUBLIC HEALTH ASSOCIATION, AMERICAN WATERWORKS ASSOCIATION, WATER POLLUTION CONTROL FEDERATION, JOINT EDITORIAL BOARD. Standard Methods for the Examination of Water and Wastewater, 15th ed., Denver, Colorado, USA, 1980, p. 185. 2 SCHWARZENBACH, G. and FLASCHKA, H. Complexometric Titrations, 2nd ed., New York, Barnes & Noble, 1969. 3 WHO. International Standards for Drinking-Water, Geneva, World Health Organization, 1971. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8:1984 © BSI 10-1999 Publications referred to See national foreword. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 01:28:07 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6068-2.8: 1984 ISO 6058:1984 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions British Standards are updated by amendment or revision. Users of British Standards should make sure that they possess the latest amendments or editions. It is the constant aim of BSI to improve t