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Preparation of a Standard for Citric Acid Analysis

Division of Applied Biology, National Research Council, Ottawa, Canada

ABSTRACT

Considerable difficulty has been experienced with crystalline citric acid as a basis for preparation of a standard solution. Both the anhydrous and monohydrate forms of the acid are unstable at room temperature and humidity, with the result that the water content can vary between 0 and 2.5 M/M. Although the anhydrous acid is stable in a desiccator, it is difficult to obtain it by drying the monohydrate, because crystals of citric acid tend to melt at temperatures above 75° C. (4). Consequently, we have studied trisodium citrate as a standard material.

The composition of trisodium citrate dihydrate was verified by analyzing two lots (reagent grade) obtained from different manufacturers. The salt was of high purity and was probably obtained by recrystallization under controlled conditions of temperature and pressure (2). Sample A was taken from a freshly opened bottle, whereas the bottle containing Sample B had been opened for at least 1 yr. No preliminary drying was given either sample before analysis.