BS 1741-8-1988 Methods for chemical analysis of liquid milk and cream - Determination of chloride content of liquid milk《奶与奶油的化学分析方法 第8部分 奶的氯化物含量的测定》.pdf

1、BRITISH STANDARD CONFIRMED OCTOBER1993 BS1741-8: 1988 Incorporating Amendment No. 1 Methods for Chemical analysis of liquid milk and cream Part8: Determination of chloride content of liquid milk UDC 637.12+637.148.074:543BS1741-8:1988 This British Standard, having been prepared under the directionof

2、 the Dairying Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 29 February1988 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment86/53332 DC ISBN 0 580 16405 5 Committees responsib

3、le for this British Standard The preparation of this British Standard was entrusted by the Dairying Standards Committee (DAC/-) to Technical Committee DAC/3, upon which the following bodies were represented: AFRC Institute of Food Research, Reading Laboratory Association of British Preserved Milk Ma

4、nufacturers Association of Public Analysts Association of Public Analysts of Scotland Creamery Proprietors Association Dairy Trade Federation Department of Trade and Industry (Laboratory of the Government Chemist) Ice Cream Alliance Limited Intervention Board for Agricultural Produce Joint Committee

5、 of the Milk Marketing Board and the Dairy Trade Federation Milk Marketing Board Milk Marketing Board for Northern Ireland Ministry of Agriculture, Fisheries and Food Royal Association of British Dairy Farmers Royal Society of Chemistry Society of Chemical Industry Society of Dairy Technology Amendm

6、ents issued since publication Amd. No. Date of issue Comments 6260 April1990 Indicated by a sideline in the marginBS1741-8:1988 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definition 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling 1 7 Procedure

7、 1 8 Expression of results 2 9 Precision 2 10 Test report 2 Publications referred to Inside back coverBS1741-8:1988 ii BSI 08-1999 Foreword This Part of BS1741 has been prepared under the direction of the Dairying Standards Committee. It is a revision of the method described in clause10 of BS1741:19

8、63, which is deleted by amendment. This revision introduces precision data. NOTEThis Part should be read in conjunction with Part1 “General introduction including preparation of samples”, published separately. A British Standard does not purport to include all the necessary provisions of a contract.

9、 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 and ii, pages1 and 2, an inside back cover a

10、nd 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.BS1741-8:1988 BSI 08-1999 1 1 Scope This Part of BS1741 describes a method for the determination of chloride content

11、of liquid milk. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definition For the purposes of this Part of BS1741, the following definition applies. 2.1 chloride content the quantity of chloride ions as determined under the conditions specified

12、 in this Part of BS1741 and expressed as a percentage by mass of the sample 3 Principle The organic matter is digested with nitric acid, followed by argentometric titration in nitric acid solution. 4 Reagents NOTESee BS1741-1. 4.1 Water complying with grade3 of BS3978. 4.2 Nitric acid, concentrated,

13、69.0% to71.0%(m/m), 20 =1.42g/mL. 4.3 Nitric acid solution, c(HNO 3 ) approximately5mol/L. 4.4 Silver nitrate solution, c(AgNO 3 ) approximately0.05mol/L. Determine the exact concentration as follows. Prepare a0.1mol/L solution of sodium chloride(NaCl) by dissolving5.844g of analytical reagent grade

14、 NaCl in1L of water.(Previously heat the sodium chloride at300 C for1h, and then allow to cool in a desiccator charged with a suitable desiccant.) Pipette10mL of the sodium chloride solution into a250mL flask and add1mL of potassium chromate indicator solution(approximately39g/L). Titrate with the s

15、ilver nitrate solution until an orange tint that persists for30s is obtained. Record the volume of silver nitrate used and calculate its concentration. 4.5 Ammonium iron(III) sulphate(ferric alum) indicator solution, saturated. Dissolve50g of ammonium iron(III) sulphate dodecahydrate (NH 4 Fe(SO 4 )

16、 2 .12H 2 O) in95mL of water and5mL of the nitric acid solution(4.3). 4.6 Potassium thiocyanate solution, approximately0.05mol/L. Pipette20mL of the silver nitrate solution (4.4) into a250mL conical flask and add25mL of water,5mL of the nitric acid(4.3) and1mL of the ferric alum indicator solution(4

17、.5). Titrate with the potassium thiocyanate solution until the solution in the flask shows an orange tint which persists for about15s. Record the volume of potassium thiocyanate solution used and calculate its concentration. 5 Apparatus Ordinary laboratory apparatus together with the following. 5.1

18、Balance, capable of weighing to an accuracy of1mg. 5.2 Conical flasks, wide-necked, of250mL capacity. 5.3 Pipette, 25mL capacity, class B, complying with BS1583. 5.4 Burette, 50mL, class B, complying with BS846. 5.5 Anti-bumping granules or glass beads 6 Sampling Take a representative sample of the

19、milk to be tested using, where appropriate, the procedures described in BS1741-1. 7 Procedure 7.1 Number of determinations Carry out duplicate determinations using two test portions from the same test sample. 7.2 Determination Weigh approximately10g of the sample, to the nearest0.01g, into a250mL co

20、nical flask(5.2). By means of a pipette(5.3) add25mL of the silver nitrate solution(4.4) and add two or three glass beads or some anti-bumping granules(5.5). Heat the contents of the flask to about80 C, add10mL of the nitric acid(4.2) and swirl the flask to mix the contents. Gently boil the contents

21、 of the flask, with occasional shaking, for a few minutes until the precipitate of silver chloride is granular and the liquid is pale yellow in colour and clear except for fat globules. Allow the contents of the flask to cool and then add60mL of water and2mL of the ferric alum indicator solution(4.5

22、). Mix thoroughly and immediately titrate the excess silver nitrate with the potassium thiocyanate solution (4.6) until the solution in the flask shows an orange tint which persists for about15s.BS1741-8:1988 2 BSI 08-1999 In the same manner, carry out a blank test, determining the equivalent of25mL

23、 of the silver nitrate solution(4.4) as thiocyanate using the same volume of reagents and water and substituting10mL of water for the test portion. 8 Expression of results Calculate the chloride content, expressed as a percentage by mass, using the following expression: Take the result as the arithm

24、etic mean of the results of the two determinations provided that the requirement for repeatability (see9.1) is satisfied. 9 Precision 9.1 Repeatability The difference between the values obtained from two determinations carried out simultaneously or in rapid succession by the same analyst using the s

25、ame apparatus shall not exceed0.005%(m/m). 9.2 Reproducibility The difference between the results obtained on samples of the same test material by two different analysts in different laboratories(where each result is the mean of two values that comply with the repeatability requirement) should not e

26、xceed0.01%(m/m). 10 Test report The test report shall be in accordance with BS1741-1. where V 1 is the volume of thiocyanate solution used in the blank titration(in mL); V 2 is the volume of thiocyanate solution used in the sample titration(in mL); C is the exact concentration of the thiocyanate sol

27、ution(in mol/L); m is the mass of the test portion(in g).0.03546 V 1 V 2 ()C m -100 BS1741-8:1988 BSI 08-1999 Publications referred to BS846, Specification for burettes. BS1583, Specification for one-mark pipettes. BS1741, Methods for chemical analysis of liquid milk and cream. BS1741-1, General int

28、roduction including preparation of samples. BS3978, Specification for water for laboratory use. BS1741-8: 1988 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards

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