Characterizing the factors that influence oxygen selectivity in gas chromatography–microwave-induced plasma atomic emission spectrometry

Abstract

Factors affecting oxygen-selective detection with gas chromatography–microwave-induced plasma atomic emission spectrometry are described. The instrumental factors include helium support gas flow, microwave power and viewing position in the plasma; position affects oxygen selectivity the most. When viewed laterally, oxygen selectivity is 4850: 1 over carbon compared with 155:1 for the axial viewing geometry. Reduction of the residual oxygen in the plasma support gas is crucial to improved oxygen selectivity, but excessive purification and concomitant reduction of hydrogen in the plasma gas results in negative responses and broad peaks. Adding 0.03% hydrogen to the plasma gas restores oxygen selectivity. Several analyte species with varied carbon and hydrogen composition and halogenation show no significant differences in oxygen sensitivity, indicating a lack of compound-specific effects in the system. Emission for recombination products of oxygen was lowest at the point in the plasma where selectivity was highest.