Studies with a miniaturized microwave induced plasma for element specific detection in gas chromatographic separations of halogenated hydrocarbons

Abstract

The possibilities of a helium microstrip microwave induced plasma, operated at less than 40 W and less than 250 mL min⁻¹ of gas, as source for optical emission spectrometry (MSP-OES) were studied for the element specific detection of halogenated volatile organic compounds, such as chlorinated and brominated alkanes and arenes, after their separation by capillary gas chromatography (GC). After hyphenation of the GC with MSP-OES with the aid of a heated transfer line, different gas chromatographic parameters, like the carrier gas flow (1.4–3.3 mL min⁻¹) and the oven temperature (100–200), as well as different plasma specific parameters, like the forward power (30–40 W) and the plasma gas flow (100–200 mL min⁻¹), were optimized. In the next step, rotational and excitation temperatures of microstrip plasma were studied in dependence on analyte concentrations between 1 and 10% v/v in pentane and found to be in the order of 1250–1650, as measured with OH bands, and 6100–6900 K, as measured with Fe-lines from ferrocene vapor entered in the plasma gas, respectively. Further, it could be shown that the hyphenated technique GC-MSP-OES can be used for the determination of volatile halogenated organic compounds under the use of an internal standard with recovery rates at the order of 90–110% at the 2–5 mg g⁻¹ level. The absolute limits of detection for volatile halogenated organic compounds, obtained with GC-MSP-OES and the Cl I 837.594 nm, Br I 827.244 nm and C I 247.856 nm, were found to be in the ng-range and the relative detection limits in pentane in the µL L⁻¹ range.