Rechercher

The procedure is based on the catalytic conversion of nitrogen present in a test portion to ammonia by heating in concentrated sulphuric acid solution. Distillation and absorption of the ammonia in an excess of standard volumetric sulphuric acid solution and back-titration with standard volumetric sodium hydroxide solution in the presence of an indicator. - Replaces ISO Recommendation R 1592-1970.

Specifies the following determinations for the substances to be tested: Measurement of pH, determination of water content, determination of free alkalinity or free acidity, determination of matter extractable by light petroleum, determination of sodium alkylarylsulphonates content, determination of sodium sulphite content, determination of sodium sulphate content, determination of sodium chloride…

Depending on the content to be estimated the method described uses three different steps for determination, i.e. drying of a known mass of butter at 102 +/- 2 degrees centigrade and weighing to determination the loss of mass, extraction of the fat from the dried butter with light petroleum or n-hexane and weighing of the residue, and calculation of the fat content by difference.

Applicable to products having As contents more than 0.2 mg/kg. The principle consists in reduction of the element to arsine in a solution of silver diethyldithiocarbamate in pyridine. Photometric measurement of the purplish- red colour produced by the colloidally dispersed silver, at the maximum of the absorption curve (wavelength approximately 540 nm).

Applicable to products having contents of AlF3 of more than 0.15 % (m/m) or of NaF of more than 0.4 % (m/m). Covers sintering of a test portion with a known quantity of sodium fluoride in a muffle furnace at a temperature of (790 10) °C. Under these conditions, aluminium fluoride in excess of that required by the stoichiometric formula AlF3 .3NaF reacts to form cryolite; extraction of the ground…

Applicable to products having contents, expressed as Na2 CO3 , more than 0.02 % (m/m). Describes the release of the carbon dioxide from a test portion by acidification and heating. Entrainment of the carbon dioxide in a flow of air and absorption in weighed absorption tubes containing soda asbestos. Specifies the weighing of the absorption tubes to determine the quantity released.

Applicable to products having Na contents, expressed as Na2 O, of equal to or more than 0.05 % (m/m). The principle bases on fusion, at a controlled temperature, of a test portion with a mixture of lithium carbonate and boric oxide or with a mixture of lithium carbonate and lithium tetraborate in a platinum or platinum-gold alloy crucible. Extraction of the fused mass with hydeochloric acid…

Applicable to products having a content, expressed as sulphur trioxide, equal to or more than 0.1 % (m/m). Bases on alkaline fusion of a test portion with a mixture of sodium carbonate and boric acid. Extraction of the fused mass with perchloric acid solution and precipitation of the sulphate ions with barium chloride in an acidified medium. Filtration on a fine-texture, ashless filter paper (…

Two cases are considered: sulphuric acid contents equal to or lower than 98 % (m/m) and sulphuric acid contents higher than 98 % (m/m). The principle is based on oxidation of a test portion with hydrogen peroxide and titration of the total acidity with a standard volumetric sodium hydroxide solution, in the presence of methyl red as indicator. - Replaces ISO Recommendation R 910-1968.