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1、BRITISH STANDARD BS 5551-4.2.3: 1987 Fertilizers Part 4: Chemical analysis Section 4.2 Determination of phosphorus Subsection 4.2.3 Method for determination of phosphorus content (quinoline molybdophosphate gravimetric method) UDC 631.8:543.21.062:546.18 Licensed Copy: sheffieldun sheffieldun, na, M
2、on Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3:1987 This British Standard, having been prepared under the direction of the Chemicals Standards Committee, was published under the authority of the Board of BSI and comes into effect on 30 September 1987 BSI 10-1999 The foll
3、owing BSI references relate to the work on this standard: Committee reference CIC/37 Draft for comment 83/54735 DC ISBN 0 580 15876 4 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Committee (CIC/-) to Technical Comm
4、ittee CIC/37 upon which the following bodies were represented: Association of Public Analysts Department of Trade and Industry (Laboratory of the Government Chemist) Fertiliser Manufacturers Association Ltd Institute of Trading Standards Administration Ministry of Agriculture, Fisheries and Food Ame
5、ndments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3:1987 BSI 10-1999i Contents Page Committees responsibleInside front cover Forewordii 1Scope and field of application1
6、 2References1 3Principle1 4Reagents1 5Apparatus1 6Procedure1 7Expression of results2 8Precision2 9Test report2 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3:1987 ii BSI 10-1999 Forewo
7、rd This Subsection of BS 5551 has been prepared under the direction of the Chemicals Standards Committee in order to standardize the determination of phosphorus in fertilizers. For some years the United Kingdom has participated in the standardization of methods of analysing fertilizers through Subco
8、mmittee 4, Chemical analysis, of Technical Committee 134, Fertilizers and soil conditioners, of the International Organization for Standardization (ISO). As international agreement is reached on the methods, it is proposed to publish them as Sections of BS 5551. The standard is published in four Par
9、ts, each Part being subdivided into Sections and, where appropriate, Subsections. The four Parts are: Part 1: Terminology and labelling; Part 2: Sampling; Part 3: Physical properties; Part 4: Chemical analysis. Part 4 is to be divided into five Sections as follows. Section 4.1: Determination of nitr
10、ogen; Section 4.2: Determination of phosphorus; Section 4.3: Determination of potassium; Section 4.4: Determination of water; Section 4.5: Determination of other constituents. This Subsection of Part 4 is based on and is technically equivalent to ISO 6598:1985 “Fertilizers Determination of phosphoru
11、s content Quinoline phosphomolybdate gravimetric method”. The technical content of this Subsection agrees with ISO 6598 except that the British Standard describing the method for extraction of phosphates soluble in mineral acids, BS 5551-4.2.2, to which reference is made in 6.1, is not technically e
12、quivalent to the corresponding International Standard to which reference is made in ISO 6598. For ease of production, it has been found convenient to reproduce the text of ISO 6598, which has been amended to refer to the appropriate British Standards. Some terminology and certain conventions are not
13、 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. In British Standards it is current practice to use the
14、symbol “mL” for millilitre rather than “ml”. This British Standard describes a method of test only and should not be used as a specification defining limits of purity. Reference to the standard should indicate that the method of test used is in accordance with this Subsection of BS 5551. A British S
15、tandard 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 cov
16、er, an inside front cover, pages i and ii, pages 1 and 2, 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 sheffield
17、un, na, Mon Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3:1987 BSI 10-19991 1 Scope and field of application This Subsection of BS 5551 specifies a gravimetric method using quinoline molybdophosphate for the determination of phosphorus (expressed as diphosphorus pentaoxide
18、) in a solution prepared from natural mineral phosphates or fertilizers. 2 References The titles of the publications referred to in this standard are listed on the inside back cover. 3 Principle Precipitation, after hydrolysis if necessary, of orthophosphate ions in the form of quinoline molybdophos
19、phate, in an acid medium and in the presence of acetone, at approximately 75 C. Filtration, washing, drying and weighing of the precipitate obtained. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only water complying with BS 3978. 4.1 Acetone, pure. 4.2 Sodium
20、molybdate dihydrate 4.3 Quinoline, pure, distilled. 4.4 Citric acid monohydrate 4.5 Nitric acid, 20 = 1,38 g/ml, 63 % (m/m) solution. NOTEIf acid of another concentration is used, adjust the volume added accordingly. 4.6 Potassium dihydrogenorthophosphate, previously dried at 105 C. 4.7 Precipitatio
21、n reagent, prepared as follows: 4.7.1 Solution A Dissolve 70 g of the sodium molybdate dihydrate (4.2) in 100 ml of water in a 400 ml beaker. 4.7.2 Solution B Dissolve 60 g of the citric acid monohydrate (4.4) in 100 ml of water in a 1 000 ml beaker. Add 85 ml of the nitric acid solution (4.5). 4.7.
22、3 Solution C Add solution A to solution B and mix. 4.7.4 Solution D Mix 35 ml of the nitric acid solution (4.5) and 100 ml water in a 400 ml beaker and add 5 ml of the quinoline (4.3). 4.7.5 Solution E Add solution D to solution C and mix. Leave overnight. Filter through a sintered glass filter, of
23、porosity P 10 or P 16 (pore size index from 4 to 16 4m) and, if necessary, filter the first part of the filtrate again until a clear filtrate is obtained. Do not wash the residue with water. Add 280 ml of the pure acetone (4.1) to the filtrate and dilute to 1 000 ml with water. The solution may be k
24、ept for 1 month in a stoppered bottle protected from sunlight and heat. 5 Apparatus Usual laboratory equipment and in particular 5.1 Conical flask, wide necked, of capacity 500 ml. 5.2 Sintered glass filter crucible, of porosity P 10 or P 16 (pore size index from 4 to 16 4m), complying with BS 1752.
25、 5.3 Oven, capable of being maintained at 250 5 C. 5.4 Flameless heating apparatus 5.5 Desiccator, containing silica gel. 6 Procedure 6.1 Aliquot portion From the solution of fertilizer obtained by extraction in accordance with BS 5551-4.2.1 or BS 5551-4.2.2, take an aliquot portion containing prefe
26、rably 10 to 20 mg of diphosphorus pentaoxide and not more than 20 ml of citrate solution. Transfer to the conical flask (5.1). Add 25 ml of the nitric acid solution (4.5). Dilute to 100 ml with water. 6.2 Determination 6.2.1 Hydrolysis If non-orthophosphates are present in the solution carry out a h
27、ydrolysis as follows. Heat the contents of the conical flask gently until they begin to boil and boil until hydrolysis is complete (generally 1 h). Ensure that losses by splashing and excessive evaporation which would reduce the original volume by more than half are avoided, for example by using a r
28、eflux condenser system. When the hydrolysis is complete, make up to the original volume with water. NOTEIf phosphorus is present in the form of orthophosphate only, the hydrolysis is not necessary. 6.2.2 Precipitation Operating under a fume hood, add, without stirring, 100 ml of the precipitation re
29、agent (4.7.5, solution E) from a measuring cylinder to the contents of the flask. Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3:1987 2 BSI 10-1999 Cover with a watch-glass and heat the flask immediately using the apparatus (5
30、.4) so that within 10 min boiling just starts (75 to 80 C) and maintain for about 30 s. Then remove the flask from the heating apparatus and allow to cool for at least 30 min. Swirl 3 or 4 times during cooling. Allow to settle. 6.2.3 Weighing of the crucible Heat the filter crucible (5.2) in the ove
31、n (5.3) maintained at 250 5 C, to constant mass. Weigh the crucible to the nearest 0,000 1 g after cooling in a desiccator (5.5) containing silica gel in good condition. 6.2.4 Filtration and washing Decant the supernatant liquid through the filter crucible (5.2), using suction. Wash the precipitate
32、in the conical flask with 30 ml of water. Decant and filter the solution. Repeat this procedure five times. Quantitatively transfer the remainder of the precipitate into the crucible. Wash four times, adding the washing water only when filtration is practically complete. Continue to apply suction un
33、til all excess liquid has been extracted. 6.2.5 Drying and weighing Wipe the outside of the crucible with a filter paper. Heat the crucible in the oven (5.3), maintained at 250 5 C, to constant mass (15 to 30 min). Cool the crucible in a desiccator (5.5) containing silica gel in good condition, tran
34、sfer to a balance and then weigh immediately to the nearest 0,000 1 g. 6.3 Check of reagents For each series of determinations, carry out a check of the reagents using only the reagents and solvents in the proportions used for the extraction (citrate solution, etc.). 6.4 Check test It is recommended
35、 that a determination on an aliquot portion, containing 10 mg of diphosphorus pentaoxide, of potassium dihydrogenorthophosphate (4.6) solution be carried out to check the validity of the method. 7 Expression of results The diphosphorus pentaoxide content, expressed as a percentage by mass, is equal
36、to where m0 is the mass, in grams, of the test portion; m1 is the mass, in grams, of the precipitate; V0 is the volume, in millilitres, of the aliquot portion taken from the extraction solution; V1 is the volume, in millilitres, of the extraction solution; 141,95 is the relative molecular mass of di
37、phosphorus pentaoxide; 4 425,84 is twice the relative molecular mass of quinoline molybdophosphate. 8 Precision 8.1 Repeatability The absolute value of the difference between two individual results (mass of quinoline molybdophosphate about 350 mg), using equal volumes of the same solution of extract
38、ion, under the same conditions (same operator, same apparatus, same laboratory and short interval of time) shall be less than 2 mg. 8.2 Reproducibility The absolute value of the difference between two individual results (mass of quinoline molybdophosphate about 350 mg), using equal volumes of the sa
39、me solutions of extraction, under different conditions (different operators, different apparatus, different laboratories and/or different times shall be less than 6 mg. 9 Test report The test report shall include the following information: a) the reference of the method used, i.e. BS 5551-4.2.3; b)
40、the results and the method of expression used; c) any unusual features noted during the determination; d) any operations not specified in this Subsection of BS 5551, or in the British Standards to which reference is made, or regarded as optional, together with any circumstances likely to have affect
41、ed the results. Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3:1987 BSI 10-1999 Publications referred to BS 1752, Specification for laboratory sintered or fritted filters including porosity grading. BS 3978, Specification for
42、water for laboratory use. BS 5551, Fertilizers. BS 5551-4, Chemical analysis. BS 5551-4.2, Determination of phosphorus. BS 5551-4.2.1, Extraction of water-soluble phosphates. BS 5551-4.2.2, Extraction of phosphates soluble in mineral acids. ISO 6598, Fertilizers Determination of phosphorus content Q
43、uinoline phosphomolybdate gravimetric method1). 1) Referred to in the foreword only. Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 14:32:49 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5551-4.2.3: 1987 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the in
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