Abstract
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 detectability 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 highly colored compound in the second step. The oxidized Purpald–aldehyde adduct 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 analysis of aldehydes using HPLC. The method was shown to form colored adducts in bulk solution and on-line using electrochemical oxidation at nickel electrodes for formaldehyde, acetaldehyde, and propionaldehyde. There was a marked increase in reaction time in bulk solution as the molecular mass of the aldehyde increased. Thus, when performing chromatography using on-line electrochemical oxidation the sensitivity of the method decreased significantly as the aldehyde molecular mass increased. Reactor design, electrode configurations, electrode potentials, and optimum reaction conditions are described.
Published Version
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