BS 4258-8-1978 Methods of test for phosphoric acid (orthophosphoric acid) for industrial use - Determination of calcium content (flame atomic absorption method)《工业用磷酸(正磷酸)试验方法 第8部分.pdf

1、BRITISH STANDARD BS 4258-8: 1978 ISO 3707:1976 Methods of test for Phosphoric acid (orthophosphoric acid) for industrial use Part 8: Determination of calcium content (flame atomic absorption method) ISO title: Phosphoric acid for industrial use (including foodstuffs) Determination of calcium content

2、 Flame atomic absorption method UDC 661.634.2:546.185 325:543.422.062:546.41BS4258-8:1978 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, waspublished under the authorityofthe Executive Boardon 31 January 1978 BSI 11-1999 The following BSI referen

3、ces relate to the work on this standard: Committee reference CIC/25 Draft for comment 75/50842 DC ISBN 0 580 09938 5 Cooperating organizations The Chemicals Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following Government depart

4、ments and scientific and industrial organizations: Association of Fatty Acid Distillers British Tar Industry Association Chemical Industries Association* Chemical Society, Analytical Division Department of Health and Social Security Department of Industry, Chemicals and Textiles Division Department

5、of Industry, Laboratory of the Government Chemist* Fertiliser Manufacturers Association Ltd.* Hydrocarbon Solvents Association Ministry of Agriculture, Fisheries and Food Ministry of Defence National Sulphuric Acid Association Paintmakers Association of Great Britain Ltd. Royal Institute of Public H

6、ealth and Hygiene Soap and Detergent Industry Association Standardization of Tar Products Tests Committee The organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Brit

7、ish Pharmacopoeia Commission Campden Food Preservation Research Association Flour Milling and Baking Research Association Institute of Metal Finishing Institution of Water Engineers and Scientists National Association of Soft Drinks Manufacturers Society of Chemical Industry Textile Institute Indivi

8、dual expert Amendments issued since publication Amd. No. Date of issue CommentsBS4258-8:1978 BSI 11-1999 i Contents Page Cooperating organizations Inside front cover Foreword ii 1 Scope 1 2 Field of application 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Procedure 1 7 Expression of results 2 8 Test

9、 report 3 Annex ISO Publications relating to phosphoric acid for industrial use 4 Publications referred to Inside back coverBS4258-8:1978 ii BSI 11-1999 Foreword This British Standard has been prepared under the direction of the Chemicals Standards Committee in order to provide methods for the analy

10、sis of phosphoric acid. For some years the United Kingdom has participated in the work of preparing methods of test applicable to phosphoric acid for industrial use, organized by Subcommittee6 (formerly Working Group7), Phosphoric acid and condensed phosphates, of Technical Committee47, Chemistry, o

11、f the International Organization for Standardization (ISO). As international agreement is reached on the methods, it is proposed to publish them as Parts of this British Standard. This Part is identical with ISO3707 “Phosphoric acid for industrial use (including foodstuffs) Determination of calcium

12、content Flame atomic absorption method”. Terminology and conventions. The text of the International Standard has been accepted as suitable for publication, without deviation, as a British Standard. Certain terminology and conventions are used, however, that are not identical with those used in Briti

13、sh Standards. Attention is therefore drawn to the following. Where the words “International Standard” relating to this publication appear, they should be interpreted as “British Standard”. The comma has been used throughout as a decimal marker. In British Standards it is current practice to use a fu

14、ll point (a full stop on the baseline) as the decimal marker. Cross references. The related ISO publications listed in theAnnex correspond to Parts of this British Standard as follows. There is no British Standard corresponding to ISO/R847 1)and it is not intended that one will be published as the m

15、ethod uses as a reagent the known carcinogen benzidine and ISO/TC47/SC6 has recommended that it be withdrawn. ISO publication Part of BS 4258 ISO/R 848 a Part 1 Determination of calcium content ISO/R 849 a Part 2 Determination of iron content ISO 2997 Part 3 Determination of sulphate content ISO 336

16、0 Part 4 Determination of fluorine content ISO 3361 Part 5 Determination of silica content ISO 3359 Part 6 Determination of arsenic content ISO 3706 Part 7 Determination of phosphorus (V) oxide content ISO 3707 Part 8 Determination of calcium content (flame atomic absorption method) ISO 3708 Part 9

17、Determination of chloride content ISO 3709 Part 10 Determination of oxides of nitrogen content ISO 4285 Part 11 Guide to sampling techniques b a At the time of publication of this British Standard, ISO/R847, ISO/R848 and ISO/R849 have not been transformed into International Standards, although they

18、are listed as such in theAnnex. b In course of preparation. 1) At the time of publication of this British Standard, ISO/R847, ISO/R848 and ISO/R849 have not been transformed into International Standards, although they are listed as such in theAnnex.BS4258-8:1978 BSI 11-1999 iii Textual error. When a

19、dopting the text of the International Standard, the error given below was noticed. This has been corrected in this British Standard. Additional information. This standard specifies methods of test only and should not be used as a specification defining limits of purity. Reference to the standard sho

20、uld be in the form of words indicating that the methods of test used comply with the requirements of BS4258. WARNING. Attention is drawn to5.1. It is essential that the atomic absorption spectrophotometer is equipped with a burner designed to operate with an acetylene/dinitrogen monoxide flame, as s

21、erious hazards will result if the wrong type of burner is used with this gas mixture. 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

22、self confer immunity from legal obligations. Clause reference Textual change Annex In ISO3707, the title of ISO4285 was incorrectly given as “Sampling technique”. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv, pages1to4, an inside back cover and a back co

23、ver. 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.iv blankBS4258-8:1978 BSI 11-1999 1 1 Scope This International Standard specifies a flame atomic absorption method for the determ

24、ination of the calcium content of phosphoric acid for industrial use (including foodstuffs). 2 Field of application The method is applicable to products having a calcium content higher than50mg/kg but, by preparation of a suitable calibration graph, the range can be extended down to10mg/kg. Soluble

25、SiO 2present in the test solution at levels lower than5g/ml does not interfere. 2.1 Special case Presence of soluble SiO 2at levels higher than5g/ml of test solution (under study). 3 Principle Addition, to a hydrochloric acid solution of the test portion, of sodium ions to promote and to stabilize t

26、he emission of calcium, and of lanthanum ions to suppress the interference of aluminium. Aspiration of the solution into an acetylene-dinitrogen monoxide flame and determination of the calcium content by photometric measurement of the absorption of the422,7nm line emitted by a hollow-cathode calcium

27、 lamp. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only water doubly distilled in borosilicate glass apparatus with ground glass joints, or water of equivalent purity. 4.1 Phosphoric acid, 40g/l solution free from calcium. Weigh, to the nearest0,1g,29g of pho

28、sphorus(V) oxide (P 2 O 5 ) and spread out in a shallow layer in a suitable dish. Allow the dish to stand in a closed vessel containing water (for example a desiccator containing water in place of a desiccant), in order to effect the initial hydration. Then dissolve the hydrated oxide in1000ml of wa

29、ter. 4.2 Hydrochloric acid, approximately6N solution. 4.3 Sodium chloride and lanthanum chloride, combined solution. Dissolve 25,5g of sodium chloride and10g of lanthanum chloride heptahydrate (LaCl 3 .7H 2 O) in water and dilute to100ml. 1 ml of this solution contains approximately100mg of Na and10

30、0mg of lanthanum chloride heptahydrate. 4.4 Calcium, standard solution, corresponding to1,000g of Ca per litre. Weigh, to the nearest 0,0001g, 2,4972g of calcium carbonate, previously dried at250 C for2h and cooled in a desiccator. Place in a beaker of convenient capacity (for example600ml) and diss

31、olve carefully in30ml of the hydrochloric acid solution (4.2). Dilute the solution and transfer quantitatively to a1000ml one-mark volumetric flask. Dilute to the mark and mix. 1 ml of this standard solution contains1,000mg ofCa. Store this solution in a bottle of material free from calcium. 4.5 Cal

32、cium, standard solution, corresponding to0,050g of Ca per litre. Transfer 50,0 ml of the standard calcium solution(4.4) to a1000ml one-mark volumetric flask, dilute to the mark and mix. 1 ml of this standard solution contains50g of Ca. Prepare this solution just before use. 5 Apparatus Ordinary labo

33、ratory apparatus, of material free from calcium, and 5.1 Atomic absorption spectrophotometer, fitted with a burner fed with acetylene and dinitrogen monoxide. 5.2 Hollow-cathode calcium lamp 6 Procedure 6.1 Test portion Weigh, by difference, to the nearest0,001g, about5g of the test sample. 6.2 Prep

34、aration of the calibration graph 6.2.1 Preparation of the standard matching solutions Into each of a series of five100ml one-mark volumetric flasks, place a quantity of the phosphoric acid solution (4.1) such that it contains the same quantity of P 2 O 5as the test portion (6.1). Add1ml of the combi

35、ned solution (4.3) and4ml of the hydrochloric acid solution (4.2) and then, respectively, the volumes of the standard calcium solution (4.5) shown in the following table. Standard calcium solution (4.5) Corresponding mass of Ca ml g 0 a 1,0 2,0 4,0 6,0 0 50 100 200 300 a Blank test on reagents of th

36、e calibration graph.BS4258-8:1978 2 BSI 11-1999 Dilute the contents of each flask to the mark and mix. NOTEIf the test solution contains less than50g of calcium (Ca) in100ml, prepare a more dilute standard calcium solution by diluting10,0ml of the standard calcium solution (4.5) to100ml. Use this we

37、aker solution to prepare a calibration graph covering the range0 to50g of Ca in100ml. The bracketing measurements (6.3.2.2) should then be carried out between two standard matching solutions differing by5g of Ca in100ml. 6.2.2 Spectrophotometric measurements 6.2.2.1 ADJUSTMENT OF THE APPARATUS FITTE

38、D WITH THE HOLLOW CATHODE CALCIUM LAMP (5.2) Switch on the current to the apparatus (5.1) a sufficient time in advance to ensure stabilization. Adjust the wavelength to about422,7nm and adjust the sensitivity and the aperture of the slit according to the characteristics of the apparatus. Adjust the

39、pressure of the acetylene and of the dinitrogen monoxide according to the characteristics of the aspirator burner. Adjust the aspiration rate to between2 and4ml/min. 6.2.2.2 MEASUREMENTS Aspirate the series of standard matching solutions(6.2.1) in the flame and measure the absorbance for each. Take

40、care to keep the aspiration rate constant throughout the preparation of the calibration graph. Aspirate water through the burner after each measurement. 6.2.3 Plotting the calibration graph Plot a graph having, for example, the numbers of micrograms of Ca contained in100ml of the standard matching s

41、olutions as abscissae and the corresponding values of the absorbances, reduced by the value for the standard matching solution No.0, as ordinates. 6.3 Determination 6.3.1 Preparation of the test solution Transfer the test portion (6.1) to a500ml one-mark volumetric flask and dilute to about250ml. Ad

42、d20ml of the hydrochloric acid solution (4.2), and5ml of the combined solution (4.3). Dilute to the mark and mix. If the calcium content is between50 and200mg/kg, carry out the measurements directly on the test solution thus obtained. If the calcium content is higher, carry out further dilutions as

43、indicated in the following table. 6.3.2 Spectrophotometric measurements 6.3.2.1 PRELIMINARY MEASUREMENT Carry out a preliminary measurement on the test solution (6.3.1) following the procedure specified in6.2.2.2, at the same time as the spectrophotometric measurements are carried out on the standar

44、d matching solutions (6.2.1). From the calibration graph (6.2.3), calculate the approximate concentration of Ca, in micrograms per100ml of the test solution (6.3.1). 6.3.2.2 BRACKETING MEASUREMENT Carry out a second measurement on the test solution (6.3.1) by bracketing between two standard matching

45、 solutions differing by only25g of Ca in100ml. To prepare these standard matching solutions, follow the procedure specified in6.2.1, using, however, suitable quantities of the standard calcium solution (4.5). 7 Expression of results The concentration C of calcium, expressed as micrograms of Ca per10

46、0ml of the test solution, is given by the formula where Expected Ca content Aliquot portion of the test solution (6.3.1) to be taken Combined solution (4.3) to be added Final volume of the solution mg/kg ml ml ml 200 to500 50 0,50 100 500 to 1000 25 0,75 100 1000 to1500 20 0,80 100 1500 to2000 10 0,

47、90 100 C 1 is the concentration, in micrograms per100ml, of the weaker bracketing solution; A 1 is the corresponding value of the absorbance; C 2 is the concentration, in micrograms per100ml, of the stronger bracketing solution; A 2 is the corresponding value of the absorbance; A 0 is the value of t

48、he absorbance corresponding to the test solution (6.3.1). CC 1 C 2 C 1 () A 0 A 1 A 2 A 1 - + =BS4258-8:1978 BSI 11-1999 3 The calcium (Ca) content, expressed in milligrams per kilogram, is given by the formula where 8 Test report The test report shall include the following particulars: a) the refer

49、ence of the method used; b) the results and the method of expression used; c) any unusual features noted during the determination; d) any operation not included in this International Standard or regarded as optional. C is the concentration of Ca, expressed as micrograms per100ml of the test solution; m is the mass, in grams, of the test portion(6.1); D is the dilution ratio (see the table in6.3.1); 5is the ratio of the volume of the test solution(6.3.1) to the volume of the calibration solutions (6.2.1). C m - 500 100 -