Real-time broad spectrum characterization of hazardous waste by membrane introduction mass spectrometry. 1998 annual progress report

摘要

As of May 1, 1998, the authors have designed and tested the rare gas ionization source and the associated ion optics. Ions are generated in a microwave plasma which can be supported by helium or argon from room air. A series of extraction and focusing lenses followed by a linear quadrupole serves to inject ions into the ion trap. Injection efficiency and favorable trapping of externally-generated ions are dependent on several parameters including lens potentials, quadrupole operation, buffer gas pressure, kinetic energy of the injected ions, and amplitude of the trapping potential. They have investigated rf-only operation of the linear quadrupole. RF/DC operation will be studied as a means for further reducing interferences. A publication on this work has been submitted to Int. J. Mass. Spectrom. Ion Proc. To date they have used MIMS to detect 40 volatile and SVOCs without preconcentration, primarily from an air matrix. The 40 analytes range in boiling point from 21 to 279 C and include chlorinated and oxygenated solvents, chlorophenols, polyaromatic hydrocarbons, and substituted benzenes. Using MIMS, they have demonstrated the direct, simultaneous detection of a volatile organic compound, a semi-volatile organic compound, and an organometallic compound with a single analytical technique in near real-time for two waste streams, air and water. To their knowledge, this is the first time this has been accomplished. They have investigated the analysis of several organometallic compounds containing heavy metals by MIMS. These include lead and tin compounds. When these molecules are analyzed, organic fragment ions are observed. However, neither the intact molecular ion, nor the metal ion species are seen in the mass spectrum. These results are interesting because in the spectra of metal compounds most of the ion current is normally carried by metal-containing species (J. Charalambous, ed., Mass Spectrometry of Metal Compounds). The authors speculate that it is oxygen, present either as a neutral or as an ionized species, that may be inhibiting the appearance of metal-containing fragment ions in certain cases. Oxygen is one of the predominating species in the ion trap environment in the experiment. Its high availability for secondary reactions as either a neutral or positively charged ion and the stability of possible products from these secondary processes may make the detection of metal-containing ions problematic in the current set-up. The formation of highly refractory neutral metal oxides, for example, would preclude the detection of metal-containing fragment ions. They are investigating experimental means to test the questions that have been raised by these observations. Other ion trap instruments in the lab with additional capabilities to study ion/molecule chemistry may provide help in testing and resolving this issue.