Potentiometric detection of amines in ion chromatography using macrocycle-based liquid membrane electrodes

Potentiometric detection employing solid-state electrodes was applied to the determination of organic amines in cation-exchange, and in ion-interaction chromatography. The amines included nine industrial alkylamines, the biogenic amines putrescine and cadaverine, the neurotransmitter acetylcholine and choline. Three PVC-based liquid membrane electrode coatings were used, incorporating respectively the lipophilic cation-exchanger tetrakis(p-chlorophenyl)borate, a combination of tetrakis(p-chlorophenyl)borate and dibenzo-18-crown-6, or a combination of tetrakis(p-chlorophenyl)borate and a calix6]arene. The three solid-state electrodes allowed sensitive detection of all amines. The addition of macrocycles with molecular recognition properties resulted in a superior sensitivity when compared to the tetrakis(p-chlorophenyl)borate-based electrode. The effect was most significant for the smaller amines which form the most stable complexes with the macrocycles. Detection limits of the order of 10⁻⁶ M (injected concentration) were measured for mono- and diamines for the macrocycle-based electrodes.