Direct Determination of Citric Acid in Milk with an Improved Pyridine-Acetic Anhydride Method

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Abstract
The optimum proportions of pyridine, acetic anhydride, water, and acetic acid, for the determination of citric acid were determined at various reaction temperatures between 17 and 60oC. The modified procedure thus developed eliminates the violent nature of the reaction, even at the high reaction temperatures. A method for the determination of 25 to 200 ug of citric acid, at a reaction temperature of 32oC, is presented and compared with previously published methods based on the reaction; improved sensitivity, stability, ana reproducibility are obtained without careful timing. Milk and serum can be analyzed directly, after suitable dilution. Results of direct analysis of milk were from 5 to 15% higher than those for the corresponding sera and are believed to represent the true values for the citric acid content of milk.