Determination of Arsenic in Organic Compounds. An Iodometric Semimicroprocedure

Abstract

THE method described'the substance is decomposed by action of sulfuric and nitric acids, and the arsenic is precipitated by hypophosphorous acid. The arsenic is collected on a filter and is then dissolved by action of excess bromine (from Koppeschaar's bromate-bromide solution) in measured amount. The excess bromine is determined iodometrically. This procedure is well suited to the analysis of relatively small (semimicro) samples, for the reason that in the oxidation in-

Photometric Determination of Arsenic in Copper and Copper-Base Alloys

“…Evans (6) states that the precipitate must first be thoroughly washed writh a 2% solution of sodium hypophosphite in 1 to 3 hydrochloric acid and finally with a 5% ammonium chloride solution. Sloviter (12) states that simply washing with hot water, freshly boiled to remove oxygen, is sufficient. The author's experience has been that hot water washing is sufficient, except in handling 5 gram samples, when a preliminary wash with 1 to 3 hydrochloric acid containing about 1% hypophosphorous acid is desirable to prevent the possible precipitation of cuprous chloride.…”

“…The method for the determination of C14 in organic compounds described in this paper makes use of a combustion train to convert the organic materials to carbon dioxide. The carbon dioxide is precipitated as barium carbonate and subjected to radioactive analysis with a Lauritsen electroscope as modified by Henriques, Kistiakowsky, Margnetti, and Schneider (4) and by Seligman (12). To eliminate necessity for determining the thickness of the precipitates, the original sample weights were chosen so as to give sufficient barium carbonate for samples of thickness greater than the range of the C14 (3-particles in barium carbonate (10).…”

“…Apart from distillation procedures, the only other separation of arsenic of general application is the precipitation of metallic arsenic, either by stannous chloride or by hypophosphorous acid (2, 4-6, 8, 10, 12, IS). Hypophosphorous acid is usually considered to be the more sensitive and generally satisfactory reagent (12).…”

Microdeterminação do arsênico

“…3 -Os métodos iodométricos (11), baseados na obtenção da arsenamina, sendo esta recebida em uma solução de cloreto mercúrico, o ácido arsenioso resultante dosado por titulação com iodo; ou o Arsênico é precipitado pelo ácido hipofosção com iodo; ou o Arsênico é precipitado pelo ácido hipofosforoso (21), dissolvido em excesso (quantidade medida) da solução de Koppeschaar (brometo e bromato potássicos), sendo o hologeno em excesso determinado por iodometria, empregando-se para tal um "buffer", o fosfato bissódico.…”