Quantification of triethanolamine through measurement of catalytic current in alkaline iron-d-gluconate solution

Abstract Triethanolamine is widely used in cosmetics and detergent formulations. Through its negative redox potential of −1050 mV (vs. Ag/AgCl, 3 M KCl) the Fe(II/III)-triethanolamine complex also is of interest as electrolyte in redox-flow batteries. Thus an analytical method to determine triethanolamine concentrations in complex formulations is of distinct technical value. In cyclic voltammetry a catalytic current is observed when Fe(III)-triethanolamine complexes are reduced in presence of an excess Fe(III)- d -gluconate. The catalytical regeneration of the Fe(III)-triethanolamine complex occurs at its characteristic cathodic peak potential ( E p ) c of −1050 mV and thus permits analytical determination of low triethanolamine concentrations. In CV experiments a linear relationship between triethanolamine concentration and ( E p ) c at −1050 mV was observed for triethanolamine concentrations between 0.05 and 1 mM in an electrolyte containing 15 mM Fe(III)- d -gluconate and 0.4 M NaOH. As an example, electrolytes from an all‑iron redox-flow cell were analysed for possible transfer of triethanolamine through the ion exchange membrane. The standard addition method was used to minimise matrix effects on the determination of the cathodic peak currents ( I p ) c . The new method permits a direct analysis of triethanolamine concentration without extensive sample preparation or highly specialised equipment. This makes the technique useful as a routine method for triethanolamine analysis in a wide range of technical applications.