SOLVENT VENTING TECHNIQUE FOR GAS-CHROMATOGRAPHY WITH MICROWAVE-INDUCED PLASMA-ATOMIC EMISSION-SPECTROSCOPY

A solvent-venting interface for gas chromatography with microwave plasma emission detection was developed. Solvent venting is necessary to avoid the deleterious effects that can occur when solvent is permitted to enter the plasma. During venting, the flow of plasma supply gas through the discharge tube is reversed. The reversed gas flow directs the solvent away from the plasma to vent through resistively heated stainless steel tubing. Gas flow direction is controlled by a 6-port valve. After venting, the valve is switched to the analysis mode, and the supply gas and column effluent flow in the forward direction to the plasma for analyte determination. Vent operation does not appear to affect plasma stability. Although a change in background is observed during solvent venting, the background quickly returns to its original level when the vent is switched back to the analysis mode. The interface is a low dead volume design that allows placement of the column 2-3 mm from the plasma. Because a transfer line or other components are not required, active sites in the interface are avoided. A modified commercial instrument (Applied Chromatography Systems MPD 850) was used for this research. Performance of the modified instrument was improved relative to that of the original system. Interface design and analytical results are reported.