(VanillylmandelicAcid)

We propose a simple and precise densitometric method for measuring vanillylmandelic acid (VMA). The method comprises direct urine application, thin-layer chromato-graphic (TLC) separation, postchromatographicderivati-zation, 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 cahbration function. The calibration function was 7.57-49.23 moI/L. This method was used to determine urinary concentrations of excreted VMA; concentrations ranged from 4.84 to 56.06 pmoI/day. IndexingTerms: thin-layer chromatography ‘ in situ post-chro-matographic derivatization 4-Hydroxy-3-methoxymandelic acid (VMA) is a cate-cholamine metabolite normally excreted in urine. Th