Organic mass spectrometry and control of fragmentation using a fast flow glow discharge ion source

Abstract

Representative organic vapors have been introduced into the flowing afterglow of a low power (<5 W) dc-glow discharge, coupled to a quadrupole mass spectrometer. When a positive bias was applied to the ion sampling orifice, the very surprising result was that molecular mass spectra were obtained with a high sensitivity. When a negative bias was applied to the ion sampling orifice, fragmentation of the analyte was observed with an increase in the extent of ion dissociation as the voltage was increased. The breakdown pattern is compound-specific and would be useful in confirming the identity of an unknown sample. When combined with chromatographic separation, the FFGD-MS technique could be used for chemical speciation studies at the sub-picogram level.

Rydberg gas theory of a glow discharge plasma: I. Application to the electrical behaviour of a fast flowing glow discharge plasma

“…This is not surprising in the sense that such sheaths are generally regarded as 'collision free'. Mass spectrometry experiments reported elsewhere for a different apparatus, 17 in which organic molecules were introduced into the downstream flowing plasma, under similar conditions, gave a collision-induced-decomposition (CID) breakdown pattern of organic ions, caused by their acceleration across the Cone sheath, which was proportional to (À)V C . Decomposition was much more efficient than in experiments conducted by Blom and Munson, 18 in a high field drift source.…”

“…Often, we find that cations go through a maximum in their intensity when V C is small and positive, before they are extinguished from the spectrum as (+)V C is increased. 17 For some ions, intensities are even greater than when V C is negative. This effect was reported previously by Taylor et al 20 for ions emerging from a conventional (low flow) GD ion source.…”

“…It is, of course, no surprise to detect cations when the sheath field is negative, but it is surprising when V C and the sheath field are both positive. 9,11,17 We would expect cations to be repelled by such a field, particularly so since the boundary layer is so narrow. For example, with a sheath potential of only 1 volt, the field strength would be ¼285 V cm À1 for a collision free boundary.…”

“…A particularly telling experiment is when organic molecules are titrated in trace amounts into the downstream flow. 17 When the Cone sheath field is negative, molecular ions created by reaction with the plasma are accelerated across the Cone sheath and become fragmented due to collision induced decomposition (CID). This effect was referred to above (section II(C), part 1).…”

Rydberg gas theory of a glow discharge plasma: II. Electrode kinetics (probe theory) and the thermal rate constant for Symmetrical charge transfer involving Rydberg atoms of Ar

“…The evidence is based on plasma reactions with H 2 and other gases, as monitored by their effect on the mass spectra, and the effect on spectra of bias potentials on the ion exit Cone. [5][6][7][8][9][10] This paper is one of a set of three which specifically address the electrical behaviour of the 'FAG' plasma. In paper I, we consider the experimental measurements.…”