Determination of vanillylmandelic acid with ion-pair chromatography and fluorescence detection

We describe a chromatographic procedure for sensitive (2.0 mumol/L), specific quantification of vanillylmandelic acid (VMA) in urine with iso-VMA as an internal standard. After rapid extraction from urine, the VMA is determined by isocratic reversed-phase ion-pair chromatography on a bonded C8 column and detection of the native fluorescence on excitation at 285 nm. The fluorescence signal is quite dependent on the pH of the mobile phase. Results by the method vary linearly with VMA concentration up to 320 mumol/L and correlate well (r = 0.9880) with those obtained by conventional ultraviolet spectrophotometry. The mean 24-h excretion of VMA from 29 healthy volunteers was 21.4 (SD 5.4) mumol.