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The transport behavior of moderately volatile analyte in a membrane desolvation system is examined. With the goal of atomic emission determination of liquid chromatographic analytes, a tubular polytetrafluoroethylene membrane desolvator interface was used to enhance the performance of a 120 W helium microwave-induced plasma atomic emission detector. To monitor organo-chlorine compounds, Cl emission was observed at 479.5 nm. Membrane desolvator conditions such as temperature, solvent composition and counter current gas flow were optimized. Converse to required conditions for non-volatile inorganic compounds, semi-volatile organic compound transport was maximized at lower membrane desolvator temperatures. Analyte transport was enhanced by modifying the solvent with dilute H2SO4. Low vapor pressure H2SO4 minimized analyte diffusion across the membrane and helped linearize the calibration plot. The detection limit of 2,6-dichlorobenzamide in pure methanol using ultrasonic nebulization and membrane desolvation with microwave-induced plasma detection was 2 ppm. Chromatographic separation and detection was demonstrated with 2,6-dichlorobenzamide and 4-chlorobenzamide. |
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