Performance evaluation of a gas chromatograph coupled to a capillary microwave-induced plasma mass spectrometer

Abstract

A gas chromatography-microwave induced plasma-mass spectrometry (GC-MIP-MS) system was built and evaluated for plasma stability and analysis of organochlorine pesticides. Studies show that the capillary MIP, 1 mm id, produces an analytically stable source. Plasma parameters (n_e=1.56×10¹⁴ cm^–3, T_exc=3784 K, T_rot=2724 K, T_ion=5500 K at flow rates of 30-500 ml min^–1) were consistent with results reported for larger sources (e.g., 100 W or greater power with gas flows >0.1 l min^–1). Analytical performance was evaluated by comparing GC-MIP-MS against GC-MS with electron impact ionization (EI). Typically, MIP-MS produced the same or larger signals for a 16 compound pesticide standard solution. However, when more than 10% diesel-oil (2+1) was added to the standard solution, significant carbon deposition occurred. Addition of the scavenger gases N₂ or O₂ allowed up to 70% diesel-oil (2+1) mixtures to be added without compromising data quality. For example, GC-MIP-MS and GC-EI-MS results were generally within 10%, with a 16 compound average precision of 15%. Although the addition of scavenger gases reduced sensitivity by 50%, it is unlikely that many real-world samples will contain such a high carbon loading.

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