[A comparison of methods of determining 4-pyridoxic acid in urine]

Routine fluorescent assays for urine 4-pyridoxic acid (4-PA) in variants of lactone 4-PA external standard (variant 1) and internal 4-PA standard (variant 2) were compared to high performance liquid chromatography. Correlation between the two values were defined by specially derived equation. The internal standard is preferable, as variant 1 presents underestimated results. Variant 2 is limited to high 4-PA concentrations, being unfit in low ones for overestimating the data. The chromatography proved most reliable and specific.