ON-LINE ELECTROCHEMICAL DETECTION FOR SUPERCRITICAL-FLUID CHROMATOGRAPHY

A self-contained electrochemical cell consisting of a working and a qu asi-reference electrode coated with a thin film of a conductive polyme r was used as a postcolumn detector for supercritical fluid chromatogr aphy (SFC-EC). Cyclic voltammetry was used to obtain chromatograms of ferrocene, anthracene, p-benzoquinone, and hydroquinone after their el ution from a Cls packed column with unmodified, acetonitrile-modified, or methanol-modified CO2. In unmodified CO2, the quantitative perform ance of the SFC-EC detection of ferrocene was similar to that obtained with a downstream mo with respect to detection limit, response linear ity, and peak shape. The baseline signal of the EC detector remained h at during density gradient elution while a noticeable drift occurred i n the baseline signal of the FID. Furthermore, whereas the mo was tota lly inoperable in a mobile phase containing similar to 3% (v/v) Of eit her acetonitrile or methanol, the EC detector functioned well in the m odified fluids. Thus, the EC detector is compatible with both unmodifi ed and modified CO2 mobile phases. A valuable feature of these newly d eveloped SFC detectors is their compatibility with a very large fracti on of the range of separation conditions that are important to SFC.