The ultramicro determination of inorganic sulphate

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Abstract
A scaled-down version of the benzidine method of Dodgson and Spencer (1953) has been developed for the estimation of 20-400 [mu]mg of SO4" in 10 [mu]l samples. The precipitated benzidine sulfate is estimated by direct spectrophotometric measurement of benzidine at 248 m[mu]. Modifications of the method for use with higher concentrations of SO4 and for 20 and 100 microliter samples are described. The scaled-down version is twice as sensitive as, and very much more rapid than, the original method. By means of the benzidine method K2SO4 can be quantitatively recovered in the presence of various tissue suspensions, sulfatase substrates and small amounts of certain inorganic ions. The barium chloranilate method has been scaled down for use with 10 microliter samples containing 0.25-2.5 or 2.5-25 [mu]g of SO4 . With the benzidine method, 3 different samples of acetone-dried liver of Charonia lampas failed to liberate SO4 from chondroitin sulfate.