Thermal modulator array for analyte modulation and comprehensive two-dimensional gas chromatography

Segmented thermal modulators were fabricated for the modulation of column effluent in one-dimensional gas chromatography, comprehensive two-dimensional gas chromatography, and as sample introduction devices in other analytical techniques. Thermal desorption of analytes from the modulator was achieved by computer-controlled application of large DC currents at low voltages sequentially to consecutive segments or stages of the modulator heaters for periods between 100 and 400 ms per segment. This procedure produced sharply focussed analyte peaks. Unsegmented heaters and heaters having 2, 4, 6, 8, and 10 segments or stages were compared with respect to their focusing efficiency. The 10-stage heater was found to give sharper focusing than heaters with a smaller number of segments. Analyte pulses with peak widths at half-height of ca. 150 ms were generated by the 10-stage heater. The application of a 10-stage modulator in a comprehensive two-dimensional analysis of a light petroleum condensate gave results of acceptable quality.