On-line deoxygenation in reductive (and oxidative) amperometric detection: environmental applications in the liquid chromatography of organic peroxides

Abstract

Cyclic voltammetry was used qualitatively to characterize and determine the feasibility of the oxidation and reduction of selected organic peroxides and hydroperoxides at a glassy carbon electrode. Organic peroxides were determined using reversed-phase high-performance liquid chromatography with simultaneous reductive and oxidative amperometric detection in a thin-layer dual parallel–adjacent electrode configuration. An on-line deoxygenator allowed the removal of molecular oxygen from the mobile phase and this resulted in an extension of the negative potential range of the glassy carbon electrode by approximately 750 ± 50 mV vs. the Ag/AgCl reference electrode. Chromatographically assisted hydrodynamic voltammetric measurements, in the dual parallel–adjacent electrode configuration, provided confirmation of the feasibility of simultaneously monitoring two independent redox reactions, for a single analyte, and allows for both the qualitative and quantitative analysis of organic peroxides (and hydroperoxides). The reductive amperometric responses were, on average, 2–5 times greater, depending on the particular organic peroxide, than the corresponding oxidative amperometric responses. An empirically determined parameter was evaluated and developed, {[i_Oxi_Red^–1] or [i_ai_c^–1]}, from two independent electrode reactions, that allows the qualitative identification of organic peroxide analytes by comparison of samples with standard injections. Estimated method detection limits (MDLs) for butan-2-one (butan-2-one) peroxide (2-BP), tert-butyl hydroperoxide (t-BHP) and cumene hydroperoxide (CHP) in reductive amperometry are approximately 0.8, 0.4 and 5 ppb, respectively and the oxidative amperometric MDLs are about 3, 2.5 and 12 ppb, respectively. The reductive amperometric responses for 2-BP, t-BHP and CHP are linear over 4–5 orders of magnitude of concentration, extending from ca. 1 µg l^–1 to ca. 100 mg l^–1, and the corresponding correlation coefficients are of the order of 0.9997–0.99994.