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Hippuric acid dissolved in pyridine producesa red-orange color upon the addition of benzenesulfonyl chloride. The color has a stable absorbance at 380 mµ. It is sensitive in microgram quantities of hippuric acid and follows the Beer-Lambert Law over a wide range of concentrations. The mechanism of the color reaction is described.
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Umberger et al. (1963) studied this question.
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