Densitometric determination of urinary 4-hydroxy-3-methoxymandelic acid (vanillylmandelic acid)
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We propose a simple and precise densitometric method for measuring vanillylmandelic acid (VMA). The method comprises direct urine application, thin-layer chromatographic (TLC) separation, postchromatographic derivatization, and in situ reading of the formed derivative at 560 nm. Quantitation was done by measuring peak area with a computer-controlled TLC Scanner and applying a five-point calibration function. The calibration function was 7.57-49.23 μmol/L. This method was used to determine urinary concentrations of excreted VMA; concentrations ranged from 4.84 to 56.06 μmol/day.