Supercritical Fluid Chromatography with Electrochemical Detection of Phenols and Polyaromatic Hydrocarbons

Abstract

A self-contained electrochemical cell consisting of a working and a counter electrode coated with a thin poly(ethylene oxide) film containing lithium triflate has been evalulated as an on-line detector for supercritical fluid chromatography. Electrochemical detection of 11 priority phenols and 13 polyaromatic hydrocarbons separated on a packed diol column with neat and methanol-modified CO2 mobile phases is described. The detector is operated voltammetrically, which permits the simultaneous detection of both oxidizable and reducible components of individual mixtures. Quantitative aspects of the detector performace have been evaluated and compared to those of a downstream flame ionization detector. The electrochemical detector provides low-nanogram detection limits and responds linearly over two decades of injected quantities. An advantage of voltammetric detection is the selectivity derived from the range of applied potentials used. Overlapping elution profiles of chloro-, methyl-, and nitro-substituted phenols can be resolved voltammetrically by capitalizing on differences between their half-wave potentials. The detector can be used for a period of at least 3 days without refurbishing. The electrochemical detector is compatible with CO2 containing 1% (v/v) methanol, which can be used to decrease the total analysis time for the phenol mixture from 50 min in unmodified CO2 to 20 min.