Atmospheric pressure helium rf plasma source for atomic and molecular mass spectrometry

A capacitively coupled low power atmospheric pressure rf He plasma established within a thermostated cylindrical steel block serves as a source for the generation of molecular and atomic ions for mass spectral analysis. Volatile analytes separated by gas chromatography are admitted to the source through a coaxial rf-powered center electrode. Variation of the forward power, in the range 5-100 W, and the position of the plasma relative to the differentially pumped extraction orifice of the mass spectrometer, permits control over the relative intensities of parent and daughter ion products of the decomposition of organometallic compounds introduced into the source. Spectral features range from simple response from atomic ions to the detection of the parent molecular compounds and combinations of the two between the extremes of operating conditions. Ferrocene, triethyllead chloride and ethylmercury chloride were used to illustrate the application of the technique.