6598 International Standard (ISO INTERNATIONAL ORGANIZATION FOR STANDARDIZATION+MEKAYHAPOAHAA OPrAHM3AUWR NO CTAHAAPTW3ALMWORGANISATION INTERNATIONALE DE NORMALISATION ANsl Internat Doc Sect Fertilizers - Determination of phosphorus content Quinoline phosphomolybdate gravimetric method Engrais-Dosageduphosphore-- Methodegravimetriqueauphosphomolybdatedequinoleine First edition-1985-09-15 OCT 9 1985 ISO 6598-1985 (E) UDC 631.8:543.21:546.185 Ref.No.ISO6598-1985(E) Descriptors : fertilizers, chemical analysis, determination of content, phosphorus, gravimetric analysis. Pricebasedon3pages Foreword ISo (the International Organization for Standardization)is a worldwide federation of national standards bodies (IsO member bodies). The work of preparing International Standards is normally carried out through iSo technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with iso, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISo Council. They are approved in accordance with Iso procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 6598 was prepared by Technical Committee ISO/TC 134, Fertilizersand soilconditioners. International Organization for Standardization, 1985 Printed inSwitzerland ISO 6598-1985 (E) INTERNATIONAL STANDARD Fertilizers - Determination of phosphorus content Quinoline phosphomolybdate gravimetric method Scope and field of application 4.6 Potassium dihydrogenorthophosphate, previously dried at 105 °C. This International Standard specifies a gravimetric method using quinoline phosphomolybdate forthe determination of 4.7 Precipitation reagent, prepared as follows: phosphorus (expressed as diphosphorus pentaoxide) in a sol- ution prepared from natural mineraf phosphates or fertilizers. 4.7.1 Solution A Dissolve 70 g of the sodium molybdate dihydrate (4.2) in 100 mi 2 References of water in a 400 ml beaker. ISO5316,Fertilizers-Extraction of water-soluble phosphates. 4.7.2 Solution B ISo 7497, Fertilizers - Extraction of phosphates soluble in Dissolve 60 g of the citric acid monohydrate (4.4) in 100 ml of mineral acids. water in a 1 000 ml beaker. Add 85 ml of the nitric acid solution (4.5). 4.7.3 Solution C 3Principle Add solution A to solution B and mix. Precipitation, after hydrolysis if necessary, of orthophosphate ions in the form of quinoline phosphomolybdate, in an acid 4.7.4 Solution D mediumand inthepresence of acetone,at approximately 75°C. Filtration, ,washing, drying and weighing of the precipitate obtained 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 Reagents Add solution D to solution C and mix. Leave overnight. Filter During the analysis, use only reagents of recognized analytical through a sintered glass filter, of porosity P 10 or P 16 (pore grade and only distilled water or water of equivalent purity. size index from 4 to 16 μm) 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 4.1 Acetone,pure. acetone (4.1) to the filtrate and dilute to 1 000 ml with water 4.2 Sodium molybdate dihydrate. The solution may be kept for 1 month in a stoppered bottle pro- tected from sunlight and heat. 4.3 Quinoline, pure, distilled. 5 Apparatus 4.4 Citric acid monohydrate. Usual laboratory equipment and in particular 4.5 Nitric acid, @20 = 1,38 g/ml, 63 % (m/m) solution. 5.1 Conical flask, wide necked, of capacity 500 ml. NOTE - If acid of another concentration is used, adjust the volume 5.2 Sintered glass filter crucible, of porosity P 10 or P 16 a