SUPERCRITICAL-FLUID CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION OF PHENOLS AND POLYAROMATIC HYDROCARBONS

A self-contained electrochemical cell consisting of a working and a co unter electrode coated with a thin poly-(ethylene oxide) film containi ng lithium triflate has been evalulated as an on-line detector for sup ercritical fluid chromatography, Electrochemical detection of 11 prior ity phenols and 13 polyaromatic hydrocarbons separated on a packed dio l column with neat and methanol-modified CO2 mobile phases is describe d. The detector is operated voltammetrically, which permits the simult aneous detection of both oxidizable and reducible components of indivi dual mixtures. Quantitative aspects of the detector performace have be en evaluated and compared to those of a downstream flame ionization de tector. The electrochemical detector provides low-nanogram detection l imits and responds linearly over two decades of injected quantities. A n 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 voltam metrically by capitalizing on differences between their half-wave pote ntials. The detector can be used for a period of at least 3 days witho ut refurbishing, The electrochemical detector is compatible with CO2 c ontaining 1% (v/v) methanol, which can be used to decrease the total a nalysis time for the phenol mixture from 50 min in unmodified CO2 to 2 0 min.