The determination of sulphate

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Abstract
Electrometric measurements showed that benzidine sulphate has a minimum solubility at pH 2.75 [plus or minus] 0.3. Solns. of sulphate as concentrated as normal human urine may be accurately analyzed at this pH. Phosphate, even in subnormal concns., interferes seriously at pH 2.75. Phosphate removal was investigated. Chloride, in physiologically possible concns., does not interfere unless the sulphate concn. is subnormal. To avoid caking of the precipitate, a special filtration technique, suitable for routine analysis, was designed. A saturated solution of benzidine sulphate in water was found to give adequate and accurate washing.