1、BRITISH STANDARD BS 4427-13: 1982 ISO 5373:1981 Methods of test for Sodium tripolyphosphate (pentasodium triphosphate) and sodium pyrophosphate (tetrasodium pyrophosphate) for industrial use Part 13: Condensed phosphates for industrial use (including foodstuffs) Determination of calcium content Flam
2、e atomic absorption spectrometric method UDC 661.833.456+661.833.458:543.422.062:546.41BS4427-13:1982 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, waspublished under the authorityofthe Board ofBSIandcomes into effect on 30 November1982 BSI 11-1
3、999 The following BSI references relate to the work on this standard: Committee reference CIC/25 Draft for comment 80/54095 DC ISBN 0 580 13080 0 Cooperating organizations The Chemicals Standards Committee, under whose direction this British Standard was prepared, consists of representatives from th
4、e following Government departments and scientific and industrial organizations: Association of Fatty Acid Distillers British Tar Industry Association Chemical Industries Association* Chemical Society, Analytical Division Consumer Standards Advisory Committee of BSI Department of Health and Social Se
5、curity Department 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 In
6、stitute of Public Health 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 Bri
7、tish Standard: 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 Amendments issued si
8、nce publication Amd. No. Date of issue CommentsBS4427-13:1982 BSI 11-1999 i Contents Page Cooperating organizations Inside front cover National 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 3 8 Test report 3 Annex A Exam
9、ples of the addition of sodium chloride solution(4.4)andphosphoric acid solution (4.3) 4 Annex B ISO publications relating to condensed phosphates forindustrialuse(including foodstuffs) 4 Table 1 2 Table 2 2 Publications referred to Inside back coverBS4427-13:1982 ii BSI 11-1999 National foreword Th
10、is British Standard has been prepared under the direction of the Chemicals Standards Committee in order to provide methods for the analysis of condensed phosphates for industrial use (including foodstuffs). This Part is identical with ISO5373 “Condensed phosphates for industrial use (including foods
11、tuffs) Determination of calcium content Flame atomic absorption spectrometric method” published in 1981 by the International Organization for Standardization (ISO). For some years the UK has participated in the work of preparing methods of test applicable to condensed phosphates for industrial use,
12、organized by subcommittee 6 (formerly working group 7) “Phosphoric acid and condensed phosphates” of Technical Committee 47 “Chemistry” of ISO. As international agreement is reached on the methods, it is proposed to publish them as Parts of this British Standard. Terminology and conventions. The tex
13、t 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
14、 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”. Cross-references. The ISO publications relating to condensed phos
15、phates for industrial use (including foodstuffs), which are listed inAnnex B, correspond to Parts of this British Standard as follows. This standard describes methods of test only and should not be used or quoted as a specification defining limits of purity. Reference to the standard should indicate
16、 that the methods of test used conform to the requirements of BS 4427. ISO publication Part of BS 4427 ISO 5372 Part 12 Condensed phosphates for industrial use (including foodstuffs) Determination of arsenic content Silver diethyldithiocarbamate photometric method (Identical) ISO 5373 Part 13 Conden
17、sed phosphates for industrial use (including foodstuffs) Determination of calcium content Flame atomic absorption method (Identical) ISO 5374 Part 14 Condensed phosphates for industrial use (including foodstuffs) Determination of chloride content Potentiometric method (Identical) ISO 5375 Part 15 Co
18、ndensed phosphates for industrial use (includingfoodstuffs) Determination of oxides of nitrogen content 3,4-Xylenol spectrophotometric method (Identical)BS4427-13:1982 BSI 11-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standard
19、s 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, pagesi toiv, pages1to4, an inside back cover and a back cover. This standard h
20、as 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 blankBS4427-13:1982 BSI 11-1999 1 1 Scope This International Standard specifies a flame atomic absorption spectrometric method for the determinati
21、on of the calcium content of condensed phosphates for industrial use (including foodstuffs). 2 Field of application The method is applicable to products having calcium contents equal to or greater than50mg/kg. The presence of soluble silica (SiO 2 ) up to 54g/ml in the test solution does not interfe
22、re. 3 Principle Preliminary hydrolysis by boiling a test portion in the presence of hydrochloric acid. Addition of sodium ions, until a constant concentration is obtained, to stabilize the promotion and emission of calcium, and addition of lanthanum chloride to increase the sensitivity of the method
23、. Aspiration of the solution into a dinitrogen monoxide-acetylene flame and determination of the calcium content by spectrometric measurement of the absorption of the422,7nm line emitted by a hollow-cathode calcium lamp. 4 Reagents During the analysis, use only reagents of recognized analytical grad
24、e and only water doubly distilled in borosilicate glass apparatus with ground glass joints, or water of equivalent purity. 4.1 Lanthanum chloride heptahydrate (LaCl 3 .7H 2 O), 100g/l solution. 4.2 Hydrochloric acid, solution containing approximately 220g of HCl per litre. 4.3 Phosphoric acid, 40 g/
25、l solution, free from calcium, corresponding to 29g of P 2 O 5per litre. Weigh, to the nearest 0,1g, 29g of phosphorus(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 p
26、lace of the desiccant), in order to effect the initial hydration. Then dissolve the hydrated phosphorus(V) oxide in 1000ml of water. NOTEIf a grade of orthophosphoric acid containing less than5mg of Ca per kilogram is available commercially, it can be used instead of phosphorus(V) oxide to prepare t
27、his solution by diluting 44g of90% H 3 PO 4solution (A approximately 1,75 g/ml), or its equivalent, to 1000ml with water. 4.4 Sodium chloride, 255 g/l solution. 1ml of this solution contains approximately 100mg of Na + . 4.5 Calcium, standard solution corresponding to1,000g of Ca 2+per litre. Weigh,
28、 to the nearest 0,0001g, 2,4972g of calcium carbonate, previously dried at about 250 C for2h and cooled in a desiccator. Place it in a beaker of suitable capacity (for example 600ml) and dissolve carefully in30ml of the hydrochloric acid solution(4.2). Dilute the solution and transfer quantitatively
29、 to a1000ml one-mark volumetric flask. Dilute to the mark and mix. 1ml of this standard solution contains 1,000 mg ofCa 2+ . Store this solution in a bottle of material free from calcium. 4.6 Calcium, standard solution corresponding to0,050g of Ca 2+per litre. Transfer 50,0ml of the standard calcium
30、 solution(4.5) to a 1000ml one-mark volumetric flask, dilute to the mark and mix. 1ml of this standard solution contains504g ofCa 2+ . Prepare this solution just before use. 5 Apparatus Ordinary laboratory apparatus, of material free from calcium, and 5.1 Atomic absorption spectrometer, equipped wit
31、h a burner designed to operate with acetylene and dinitrogen monoxide. 5.2 Hollow-cathode calcium lamp 6 Procedure WARNING The use of the dinitrogen monoxideacetylene flame presents some hazards. Handle the gases with suitable precautions and operate the apparatus under an efficiently ventilated fum
32、e hood. 6.1 Test portion Weigh, to the nearest 0,0002g, about5g of the test sample. 6.2 Preparation of the calibration graph 6.2.1 Preparation of standard matching solutions Into each of a series of five100ml one-mark volumetric flasks, place a quantity of the phosphoric acid solution (4.3) such tha
33、t its P 2 O 5concentration is the same as that of the test solution (6.3.1) (see for exampleAnnex A). Add5ml of the sodium chloride solution (4.4) and5ml of the hydrochloric acid solution (4.2) and then, respectively, the volumes of the standard calcium solution (4.6) shown inTable 1.BS4427-13:1982
34、2 BSI 11-1999 Table 1 To each flask, add1ml of the lanthanum chloride solution (4.1), dilute to the mark and mix. NOTEThe total quantity of calcium contained in the reagents used for the preparation of the standard matching solutions except the standard calcium solution (4.6), should be lower than50
35、4g. 6.2.2 Adjustment of the apparatus Fit the hollow-cathode calcium lamp (5.2) in the apparatus (5.1), switch on the current and allow to stabilize. Adjust the current, the sensitivity and the aperture of the slit according to the characteristics of the apparatus. Adjust the wavelength in the regio
36、n of422,7nm to maximum absorbance. Adjust the pressure of the acetylene and of the dinitrogen monoxide according to the characteristics of the aspirator/burner. Adjust the aspiration rate to between2and4ml/min. 6.2.3 Spectrometric measurements Aspirate the series of standard matching solutions(6.2.1
37、) in succession into the flame and measure the absorbance for each. Take care to keep the aspiration rate constant throughout the preparation of the calibration graph. Aspirate water through the burner after each measurement. 6.2.4 Plotting the graph Plot a graph having, for example, the masses, in
38、micrograms, of Ca 2+contained in100ml of the standard matching solutions as abscissae, and the corresponding values of the measured absorbance, corrected for the value of the absorbance measured in the blank test on reagents for calibration (6.2.1 zero term), as ordinates. 6.3 Determination 6.3.1 Pr
39、eparation of the test solution Transfer the test portion (6.1) to a beaker of suitable capacity (for example600ml) and dissolve it in250ml of water and 25ml of the hydrochloric acid solution(4.2). Cover the beaker with a clock glass and boil for20min. Cool the solution and transfer it quantitatively
40、 to a500ml one-mark volumetric flask. Add5ml of the lanthanum chloride solution(4.1) and the amount of sodium chloride solution (4.4) required to obtain a sodium concentration of approximately5mg/ml in the final solution, including the sodium contained in the test portion (6.1) (see for example Anne
41、x A which refers to pure products). Dilute to the mark and mix. If the calcium content is between 50and200mg/kg, carry out the measurements directly on the test solution thus obtained. If the calcium content is higher, carry out further dilutions as indicated inTable 2. Table 2 Standard calcium solu
42、tion (4.6) Corresponding mass of Ca ml 4g 0 a 1,0 2,0 4,0 6,0 0 50 100 200 300 a Blank test on reagents for calibration. Expected Ca content Aliquot portion ofthe test solution(6.3.1) tobetaken Hydrochloric acid solution (4.2) to be added Sodium chloride solution (4.4) to be added Lanthanum chloride
43、 solution(4.1) tobeadded Final volume ofthesolution mg/kg ml ml ml ml ml 200 to500 500 to 1000 1000 to 1500 1500 to 2000 50 25 20 10 2,50 3,75 4,00 4,50 2,50 3,75 4,00 4,50 0,50 0,75 0,80 0,90 100 100 100 100BS4427-13:1982 BSI 11-1999 3 6.3.2 Spectrometric measurements 6.3.2.1 Preliminary measuremen
44、t Carry out a preliminary measurement on the test solution (6.3.1) following the procedure specified in6.2.3, at the same time as the spectrometric measurements are carried out on the standard matching solutions (6.2.1). From the calibration graph (6.2.4), calculate the approximate concentration of
45、Ca 2+in100ml 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) following the procedure specified in6.2.3, by bracketing between two standard matching solutions of composition similar to that of the standard matching solutions (6.
46、2.1), but havingCa 2+contents which differ by 254g/100ml. To prepare these standard matching solutions, follow the procedure specified in6.2.1, using, however, suitable quantities of the standard calcium solution (4.6). 7 Expression of results 7.1 Concentration of the test solution The calcium conce
47、ntration, c, expressed in micrograms of Ca 2+per100ml of the test solution, is given by the formula where 7.2 Content of the sample 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)
48、an identification of the sample; b) the reference of the method used; c) the results and the method of expression used; d) any unusual features noted during the determination; e) any operation not included in this International Standard, or regarded as optional. c 1 is the concentration, in microgra
49、ms per100ml, of the standard matching solution of lower concentration, used for the bracketing measurement (6.3.2.2); A 1 is the corresponding value of absorbance; c 2 is the concentration, in micrograms per100ml, of the standard matching solution of higher concentration, used for the bracketing measurement(6.3.2.2); A 2 is the corresponding value of absorbance; A 0 is the value of absorbance corresponding to the test solution(6.3.1). cc 1 c 2 c 1 () A 0 A 1 A 2 A 1 - + = c is the calcium concentration, expressed in
