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 631.8:543.21.062:546.18BS5551-4.2.3:1987 This British Standard, havin
2、g been prepared under the directionof the Chemicals Standards Committee, was published under the authorityofthe Board of BSIandcomes intoeffect on 30September1987 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference CIC/37 Draft for comment 83/54735 DC IS
3、BN 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 Committee CIC/37 upon which the following bodies were represented: Association of Public Analysts Department of Trade and
4、 Industry (Laboratory of the Government Chemist) Fertiliser Manufacturers Association Ltd Institute of Trading Standards Administration Ministry of Agriculture, Fisheries and Food Amendments issued since publication Amd. No. Date of issue CommentsBS5551-4.2.3:1987 BSI 10-1999 i Contents Page Committ
5、ees responsible Inside front cover Foreword ii 1 Scope and field of application 1 2 References 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Procedure 1 7 Expression of results 2 8 Precision 2 9 Test report 2 Publications referred to Inside back coverBS5551-4.2.3:1987 ii BSI 10-1999 Foreword This Sub
6、section of BS5551 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 Subcommittee4, Ch
7、emical analysis, of Technical Committee134, 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 BS5551. The standard is published in four Parts, each Part b
8、eing 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 nitrogen; Section 4
9、.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 Part4 is based on and is technically equivalent to ISO6598:1985 “Fertilizers Determination of phosphorus content Quinoli
10、ne phosphomolybdate gravimetric method”. The technical content of this Subsection agrees with ISO6598 except that the British Standard describing the method for extraction of phosphates soluble in mineral acids, BS5551-4.2.2, to which reference is made in6.1, is not technically equivalent to the cor
11、responding International Standard to which reference is made in ISO6598. For ease of production, it has been found convenient to reproduce the text of ISO6598, which has been amended to refer to the appropriate British Standards. Some terminology and certain conventions are not identical with those
12、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 symbol “mL” for millil
13、itre 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 BS5551. A British Standard does not purpor
14、t 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 cover, an inside front cov
15、er, pages i and ii, pages1 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.BS5551-4.2.3:1987 BSI 10-1999 1 1 Scope and field of applicat
16、ion This Subsection of BS5551 specifies a gravimetric method using quinoline molybdophosphate for the determination of phosphorus (expressed as diphosphorus pentaoxide) in a solution prepared from natural mineral phosphates or fertilizers. 2 References The titles of the publications referred to in t
17、his standard are listed on the inside back cover. 3 Principle Precipitation, after hydrolysis if necessary, of orthophosphate ions in the form of quinoline molybdophosphate, in an acid medium and in the presence of acetone, at approximately75 C. Filtration, washing, drying and weighing of the precip
18、itate obtained. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only water complying with BS3978. 4.1 Acetone, pure. 4.2 Sodium 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. NOTE
19、If acid of another concentration is used, adjust the volume added accordingly. 4.6 Potassium dihydrogenorthophosphate, previously dried at105 C. 4.7 Precipitation reagent, prepared as follows: 4.7.1 Solution A Dissolve 70 g of the sodium molybdate dihydrate(4.2) in100ml of water in a400ml beaker. 4.
20、7.2 Solution B Dissolve 60 g of the citric acid monohydrate(4.4) in100ml of water in a1000ml beaker. Add85ml of the nitric acid solution (4.5). 4.7.3 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) and100ml water in a400ml beaker and add5
21、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 porosity P10or P16(pore size index from4to164m) and, if necessary, filter the first part of the filtrate again until a clear filtrate is obtained. Do not wash
22、the residue with water. Add280ml of the pure acetone (4.1) to the filtrate and dilute to1000ml with water. The solution may be kept for1month in a stoppered bottle protected from sunlight and heat. 5 Apparatus Usual laboratory equipment and in particular 5.1 Conical flask, wide necked, of capacity50
23、0ml. 5.2 Sintered glass filter crucible, of porosity P10orP16(pore size index from4 to164m), complying with BS1752. 5.3 Oven, capable of being maintained at250 5 C. 5.4 Flameless heating apparatus 5.5 Desiccator, containing silica gel. 6 Procedure 6.1 Aliquot portion From the solution of fertilizer
24、obtained by extraction in accordance with BS5551-4.2.1 or BS5551-4.2.2, take an aliquot portion containing preferably10to20mg of diphosphorus pentaoxide and not more than20ml of citrate solution. Transfer to the conical flask (5.1). Add25ml of the nitric acid solution (4.5). Dilute to100ml with wate
25、r. 6.2 Determination 6.2.1 Hydrolysis If non-orthophosphates are present in the solution carry out a hydrolysis as follows. Heat the contents of the conical flask gently until they begin to boil and boil until hydrolysis is complete (generally1h). Ensure that losses by splashing and excessive evapor
26、ation which would reduce the original volume by more than half are avoided, for example by using a reflux 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.
27、2.2 Precipitation Operating under a fume hood, add, without stirring,100ml of the precipitation reagent(4.7.5, solution E) from a measuring cylinder to the contents of the flask.BS5551-4.2.3:1987 2 BSI 10-1999 Cover with a watch-glass and heat the flask immediately using the apparatus (5.4) so that
28、within10min boiling just starts (75to80 C) and maintain for about30s. Then remove the flask from the heating apparatus and allow to cool for at least30min. Swirl3or4times during cooling. Allow to settle. 6.2.3 Weighing of the crucible Heat the filter crucible (5.2) in the oven (5.3) maintained at250
29、 5 C, to constant mass. Weigh the crucible to the nearest0,0001g 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 in the conical flask with30m
30、l 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 until all excess liquid has been
31、 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 at250 5 C, to constant mass (15to30min). Cool the crucible in a desiccator (5.5) containing silica gel in good condition, transfer to a balance and then weigh i
32、mmediately to the nearest0,0001g. 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 that a determination on an aliquot p
33、ortion, containing10mg 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 to where m 0is the mass, in grams, of t
34、he test portion; m 1is the mass, in grams, of the precipitate; V 0is the volume, in millilitres, of the aliquot portion taken from the extraction solution; V 1is the volume, in millilitres, of the extraction solution; 141,95 is the relative molecular mass of diphosphorus pentaoxide; 4 425,84 is twic
35、e 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 about350mg), using equal volumes of the same solution of extraction, under the same conditions (same oper
36、ator, same apparatus, same laboratory and short interval of time) shall be less than2mg. 8.2 Reproducibility The absolute value of the difference between two individual results (mass of quinoline molybdophosphate about350mg), using equal volumes of the same solutions of extraction, under different c
37、onditions (different operators, different apparatus, different laboratories and/or different times shall be less than6mg. 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) the results and the method of expression used;
38、c) any unusual features noted during the determination; d) any operations not specified in this Subsection of BS5551, or in the British Standards to which reference is made, or regarded as optional, together with any circumstances likely to have affected the results.BS5551-4.2.3:1987 BSI 10-1999 Pub
39、lications referred to BS 1752, Specification for laboratory sintered or fritted filters including porosity grading. BS 3978, Specification for 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-so
40、luble phosphates. BS 5551-4.2.2, Extraction of phosphates soluble in mineral acids. ISO 6598, Fertilizers Determination of phosphorus content Quinoline phosphomolybdate gravimetric method 1) . 1) Referred to in the foreword only.BS 5551-4.2.3: 1987 BSI 389 Chiswick High Road London W4 4AL BSIBritish
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