Pulsed electrochemical detection at gold electrodes applied to monoamines and diamines following their chromatographic separation

Pulsed electrochemical detection (PED) is applied at Au electrodes for the determination of aliphatic amines in alkaline media. Here, this detection system is demonstrated for aliphatic monoamines separated from acidic media using a high-capacity cation-exchange column and aliphatic diamines separated from acidic media using a low-capacity cation-exchange column. Post-column addition of NaOH is used to provide the alkaline environment necessary for detection of the amines at Au electrodes. In 0.1 M NaOH, pulsed voltammetric data show that a waveform with a detection potential (EDET) of 0.2 V vs. SCE provides the best response for aliphatic amines. However, addition of acetonitrile to optimize chromatographic separations requires an increase in EDET to values ranging from 0.25 to 0.6 V for monoamines and from 0.4 to 0.6 V for diamines. Limits of detection for 25-μl injections of aqueous samples are ca. 100 nM (2.5 pmol) for monoamines and ca. 200 nM (5.0 pmol) for diamines. The relative standard deviation (R.S.D.) for eight successive injections of 100 μM ethylamine is 0.3%.