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Deuterium Ion Source for the Plasma Chromatograph/Mass Spectrometer

IP.com Disclosure Number: IPCOM000060857D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Needham, CD: AUTHOR

Abstract

Ambiguities may exist in identifying the parent ion mass in a plasma chromatograph/mass spectrometer where proton donation or hydride abstraction is the mechanism for ion formation. Disclosed herein is a process which introduces a supply of heavy water into the flowing gas so that comparisons may be made to correctly determine the parent mass. The plasma chromatograph is highly sensitive, but its selectivity is rather poor. Organic vapors from the test sample are carried in a stream of nitrogen into a reaction zone where the neutral molecules undergo collision with the reactant ions formed from trace amounts of water in the carrier.

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Deuterium Ion Source for the Plasma Chromatograph/Mass Spectrometer

Ambiguities may exist in identifying the parent ion mass in a plasma chromatograph/mass spectrometer where proton donation or hydride abstraction is the mechanism for ion formation. Disclosed herein is a process which introduces a supply of heavy water into the flowing gas so that comparisons may be made to correctly determine the parent mass. The plasma chromatograph is highly sensitive, but its selectivity is rather poor. Organic vapors from the test sample are carried in a stream of nitrogen into a reaction zone where the neutral molecules undergo collision with the reactant ions formed from trace amounts of water in the carrier. The common positive reactant ions are NH4 +, NO+, H(H2O)x+ There are two principal mechanisms for the formation of product ions from the reactant ions and the neutral organic molecule (R): proton donation: R + NH4+ --> RH+ + NH3 hydride abstraction: RH + NO+ --> R+ + HNO Product ions (along with any residual reactant ions) are gated into an electric field where time-of-flight through a drift tube is measured. Ion mobility, which is a function of the molecular weight and the collision cross-section of the molecule, may thereby be calculated. Because of the low resolution of the ion mobility, a tandem quadrupole mass spectrometer is used to sample product ions so that their molecular masses may be determined. From this the possible identifications for an unknown species may be deduced. However, the mass of the parent species depends upon the reaction mechanism, which in general, is unknown. For proton donation, the parent has a mass of one less than the observed product ion, while for hydride abstract...