POSTCOLUMN OXIDATION OF PURPALD-ALDEHYDE ADDUCTS AT NICKEL ELECTRODES

Purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole), a chromogenic agent for the detection of aldehydes after TLC has been studied as a possible post-column derivatizing agent for improving the detectabilit y of aldehydes after HPLC separation. In the first step of a two step reaction, Purpald forms a colorless adduct with aldehydes. Subsequent oxidation of the colorless adduct by air or other means yields a highl y colored compound in the second step. The oxidized Purpald-aldehyde a dduct is deep purple in color and has an absorption maximum at 550 nm. An on-line post-column electrochemical reactor has been investigated as a possible alternative to air or chemical oxidation for the analysi s of aldehydes using HPLC. The method was shown to form colored adduct s in bulk solution and on-line using electrochemical oxidation at nick el electrodes for formaldehyde, acetaldehyde, and propionaldehyde. The re was a marked increase in reaction time in bulk solution as the mole cular mass of the aldehyde increased. Thus, when performing chromatogr aphy using on-line electrochemical oxidation the sensitivity of the me thod decreased significantly as the aldehyde molecular mass increased. Reactor design, electrode configurations, electrode potentials, and o ptimum reaction conditions are described. (C) 1998 Elsevier Science B. V. All rights reserved.