Comparison of potential-time waveforms for the detection of biogenic amines in complex mixtures following their separation by liquid chromatography

Pulsed amperometric detection (PAD), integrated voltammetric detection (IVD), and integrated square-wave detection (ISWD) at gold electrodes are compared for the now injection detection of 1,3-diaminopropane in a liquid chromatograph (LC). These detection methods are especially significant for alkylamines and amino acids because (i) the majority of these compounds do not naturally possess chromophoric or fluorophoric functional groups and (ii) their amperometric detection at constant potential at Au electrodes fails because the electrode activity is severely attenuated by the formation of an inert surface oxide (AuO). The anodic response mechanisms for detection of amines require concomitant formation of AuO; therefore, a large background signal is observed with conventional PAD. In comparison, the background is much smaller for IVD and ISWD because the anodic charge for oxide formation (positive scan/step) is compensated by the cathodic charge for oxide reduction (negative scan/step). The limits of detection (S/N = 3) for 1,3-diaminopropane by LC-PAD, LC-IVD and LC-ISWD are about 3 x 10(2) pg (4 pmol), 5 x 10(1) pg (0.7 pmol), and 3 x 10(1) pg (0.5 pmol), respectively, for 25-mu L injections. Results are also shown to demonstrate ISWD for detection of nine biogenic amines following their chromatographic separation.