LOW-PRESSURE INDUCTIVELY-COUPLED PLASMA ION-SOURCE FOR MOLECULAR AND ATOMIC MASS-SPECTROMETRY

A low-pressure inductively coupled plasma system is described which can be used for both molecular and atomic mass spectrometry. Element-selective detection of organotin, organolead, organoiron, and organohalide compounds was possible using this source coupled with gas chromatography. Detection limits were as follows: tetraethyllead, 13 pg; tetrabutyltin, 35 pg; ferrocene, 33 pg; iodobenzene, 25 pg; bromobenzene, 50 pg; and chlorobenzene, 500 pg. By decreasing the power and plasma gas flow it was possible to sustain a helium plasma using only the carrier gas from the gas chromatograph, and mass spectra were obtained for chlorobenzene, bromobenzene, and iodobenzene that were similar to those obtainable using an electron impact ionization source. The molecular ion for chlorobenzene was observed to 10 ng injected on-column. The effect of power on the mass spectrum was investigated. By adjusting the plasma gas flow and forward power, it was possible to influence the degree of fragmentation of the organic species. The potential exists for the development of a variable ion source with the ability to adjust the degree of fragmentation simply and rapidly.