Simultaneous determination of tetrahydro-beta-carbolines and beta-carbolines

Reversed-phase ion-pair HPLC with fluorimetric detectors connected in series was studied for the simultaneous determination of two tetrahydro-beta-carbolines and two beta-carbolines; After addition of internal standards the samples were reacted with fluorescamine, and then subjected to serial extractions to remove their precursor (tryptamine) from the analytical system. This treatment not only suppressed the artefactual formation of tetrahydro-beta-carbolines and beta-carbolines during analysis, but also effectively purified them. Under optimum conditions, using trifluoroacetic acid as counter ion, all analytes were separated within 14 min and without major interfering peaks. The quantitative ranges were 0.25-80.0 ng mL(-1) for both tetrahydro-beta-carbolines and 0.1-30.0 ng mL(-1) for both beta-carbolines. Replicate spiking experiments showed that recovery from most of the samples tested was over 90 % and the relative standard deviation ranged from 0.7 to 10.4 % within and between assays. The proposed method was applicable to various materials such as soy sauce, vinegar, ketchup, tabasco, beer, wine, sake, whisky, brandy, cows' milk, coffee, cocoa, cheese, cigarette smoke and urine.