1、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/.3:663.63:54
2、3.24:546.41BS6068-2.8:1984 This British Standard, having been prepared under the directionof the Environment andPollution Standards Committee, was published underthe authority of the BoardofBSI and comes intoeffecton 31December 1984 BSI 10-1999 The following BSI references relate to the work on this
3、 standard: Committee reference EPC/44 Draft for comment 83/50597 DC ISBN 0 580 14198 5 Amendments issued since publication Amd. No. Date of issue CommentsBS6068-2.8:1984 BSI 10-1999 i Contents Page National foreword ii 1 cope and field of application 1 2 References 1 3 Principle 1 4 Reagents 1 5 App
4、aratus 2 6 Sampling and samples 2 7 Procedure 2 8 Expression of results 2 9 Precision 2 10 Interferences 2 11 Test report 3 Bibliography 4 Publications referred to Inside back coverBS6068-2.8:1984 ii BSI 10-1999 National foreword This Section of this British Standard, which has been prepared under t
5、he direction of the Environment and Pollution Standards Committee, is identical with ISO6058:1984 “Water quality Determination of calcium content EDTAtitrimetric method”. The International Standard was prepared by subcommittee 2, Physical, chemical and biochemical methods, of Technical Committee 147
6、, 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 a
7、re being, or will be, published in Parts 1 to 6 which, together with 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. Termino
8、logy 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 com
9、ma 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 St
10、andards 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 Britis
11、h 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 Standards Corresponding British
12、 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 2:1982 Section 6.2:1983 Guidance on sampling techniques (Identical) International Standard Corresponding British Standard ISO 5667-3 BS 6068 Water qua
13、lity Section 6.3 Guidance on the preservation and handling of samplesBS6068-2.8:1984 BSI 10-1999 iii 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
14、846:1980,25mL nominal capacity, smallest scale interval0.05mL, 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 it
15、self confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to 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 ind
16、icated in the amendment table on the inside front cover.iv blankBS6068-2.8:1984 BSI 10-1999 1 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, surfac
17、e 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
18、 contents ranging from2to100mg/l(0,05 to 2,5mmol/l). For waters containing more calcium than 100mg/l, a diluted sample shall be used. 2 References ISO 385-1, Laboratory glassware Burettes Part1: General requirements 1) . ISO 5667, Water quality Sampling Part1:Guidance on the design of sampling progr
19、ammes Part 2: Guidance on sampling techniques Part 3: Guidance on the preservation and handling of samples 2) . 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,
20、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
21、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 8g of sodium hydroxide in100ml of freshly distilled water. Store in a polyethylene bottle. NOTETake precaut
22、ions to avoid contamination by atmospheric carbon dioxide. 4.2 EDTA, standard volumetric solution, c(Na 2 EDTA) . 10 mmol/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) at 80 C for2h, dissolve3,725g of the dry salt in water and dilute to1000
23、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. Use20,0ml of the calcium s
24、tandard 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 c 2is the concentration, expressed in millimoles per litre, of the calcium standard reference sol
25、ution (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. 4.3 Calcium, standard reference solution, c(CaCO 3 )= 10mmol/l. Dry a sample of pure calcium carbonate for2h at150 C, and
26、allow to cool to room temperature in a desiccator. Place 1,001g in a 500ml conical flask, and moisten it with water. Add dropwise 4mol/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 ro
27、om temperature and add a few drops of methyl red indicator solution. Add3mol/l ammonia solution until the solution turns orange. Transfer the solution quantitatively to a1000ml one-mark volumetric flask and make up to the mark with water. 1ml of the solution contains0,400 8mg (0,01 mmol) of calcium.
28、 NOTECommercially available solutions may be used. 1) At present at the stage of draft. (Partial revision of ISO/R385:1964.) 2) At present at the stage of draft. c 1 c 2 V 1 V 2 - =BS6068-2.8:1984 2 BSI 10-1999 4.4 HSN, indicator. Mix thoroughly 0,2 g HSN 2-hydroxy-1 (2-hydroxy-4-sulfo-1-naphthylazo
29、)-3-naphthoic acid (C 21 H 14 N 2 O 7 S3H 2 O) and100g 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 (C 30 H 26 N 2 O 13 ). 5 Appar
30、atus Ordinary laboratory apparatus, and: Burette, 25 ml capacity, graduated in divisions of0,05ml, conforming to the requirements ofISO385-1, class A, or equivalent equipment. 6 Sampling and samples The samples should be taken in accordance with the relevant parts ofISO5667. 7 Procedure 7.1 Preparat
31、ion of the test portion The test portion should contain between 2 and100mg/l (0,05 and 2,5mmol/l) of calcium. If a concentration in excess of100mg/l (2,5mmol/l) is expected, dilute a known volume of test solution so as to bring the concentration within the required range and record the dilution fact
32、or 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 pipe
33、tte, transfer50,0ml of the test solution to a250ml conical flask. Add2ml of thesodium hydroxide solution (4.1) and approximately0,2g 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
34、 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, c Ca , expressed in millimoles per litre,
35、is given by the equation where c 1is the concentration, expressed in millimoles per litre, of the EDTA solution; V 0is the volume, in millilitres, of the test portion; V 3is the volume, in millilitres, of EDTA used in the titration. If required, the calcium content, Ca , expressed in milligrams per
36、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 5mg/l
37、in the range30to100mg/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 zin
38、c 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 than1mg/l precipitates calcium at the pH of the titration. Calcium carbonate may precipitate if the determination is p
39、erformed too slowly or if the calcium content is high (above100mg/l or2,5mmol/l). c Ca c 1 V 3 V 0 - = Ca c 1 V 3 V 0 -A =BS6068-2.8:1984 BSI 10-1999 3 Interfering metal ions can be masked. The interference from iron at concentrations of30mg/l or less can be masked by the addition of either250mg of
40、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 interfe
41、rences 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
42、) the result, expressed in milligrams per litre, to the nearest1mg/l, or 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
43、the results.BS6068-2.8:1984 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 SCHW
44、ARZENBACH, 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.BS6068-2.8:1984 BSI 10-1999 Publications referred to See national foreword.BS 6068-2.8: 1984 ISO 6058:1984 BSI
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