Electrochemical Study and Determination of All-trans-Retinol at Carbon Paste Electrode Modified by a Surfactant

The oxidation mechanism of all-trans-retinol (vitamin A(1)) and its several esters in non-aqueous, aqueous organic mixture, and pure aqueous media was investigated by cyclic voltammetry. The oxidation occurred in several irreversible steps. The calculated highest density of electrons in retinoid molecules which are delocalized over carbon atoms of the five conjugated double bonds (C5-C14) was found in the part of the molecule involved in oxidation processes. The most sensitive oxidation peak (at +0.8 V vs. Ag/AgCl) was used for development of new direct voltammetric method based on differential pulse voltammetry for the determination of retinol at carbon paste electrode modified with surfactant sodium dodecyl sulfate (CPE/SDS). The results show that 30% (by mass) of modifier SDS exhibited optimal sensitivity and shape of voltammograms. Compared to commonly used glassy carbon electrode (GCE), the CPE/SDS showed significant progress in the retinol electroanalysis. The linear ranges for retinol determination were 1.5·10(−6)–1.8·10(−4) M for CPE/SDS and 4.4·10(−6)–7.0·10(−4) M for GCE with the detection limits of 1.3·10(−6) and 4.6·10(−7) M, respectively.