High-pressure liquid chromatographic assay of folic acid: a collaborative study.

A collaborative study of the USP high-pressure liquid chromatographic assay for folic acid was performed. Two samples were analyzed in duplicate by 14 participating laboratories. Relative standard deviations for a single determination (RSDS) ranged from +/-0.40 to +/-2.39%. Based on an analysis of variance, it was concluded that the method of peak measurement was a major determinant of reproducibility and that graphical measurement was associated with a high standard deviation. Adequate resolution was obtained using a variety of columns and operating conditions. The interlaboratory RSDS was +/-1.8%.