Determination of α,4-dihydroxy-3-methoxybenzeneacetic acid (vanilmandelic acid) by flow injection analysis coupled with luminol–hexacyanoferrate(III) chemiluminescence detection

A simple and robust method for the determination of the clinically significant molecule vanilmandelic acid (α,4-dihydroxy-3-methoxybenzeneacetic acid, 4-hydroxy-3-methoxymandelic acid) using flow injection analysis with chemiluminescence detection is described. This compound was found to enhance the chemiluminescence from the reaction of luminol with hexacyanoferrate(III) in a basic medium. The calibration function obtained over the range from 2.5 × 10–8 to 1.0 × 10–6 mol dm–3 approximated to linearity (r2 = 0.9995) with the equation of best fit of y = 1.72 × 108x + 36.9, where y is the integrated signal (V s) and x is the concentration (mol dm–3). Precision (as measured by relative standard deviation) was 2.6% for 5 replicate analyses of a standard (2.5 × 10–7 mol dm–3) and the limit of detection (3σ) was 2 × 10–8 mol dm–3. Preliminary investigations revealed that the structurally similar homovanillic acid inhibits the emission of chemiluminescence from the luminol–hexacyanoferrate(III) reaction and that the kinetics of light emission were different from those of the vanilmandelic acid enhanced reaction.