Electrospray ionization mass spectrometry and its environmental applications
An electrospray ionization (ESI) source was designed, fabricated and then installed on a VG TRIO-2 quadrupole mass spectrometer. A gold coated 50-[mu]m fused silica capillary was used instead of the conventional stainless steel needle. Analytes are desorbed into the gas phase via a heated metal transport capillary and are focused through a set of five electrostatic lenses into the analyzer region of the mass spectrometer. Environmentally significant compounds such as pesticides and herbicides that are polar, nonvolatile and thermally labile are not readily analyzed by conventional gas chromatography/mass spectrometry (GC/MS). Thirty pesticides from the 13 classes of carbamate, organophosphorus, organochlorine, bipyridyl, phthalimide, urea, carboxyllic acid, hydroxycoumarin, triazine, indandione, dinitroaniline, pyrethrin, and thiocarbamate were analyzed using this method. Analysis of these samples showed that addition of acid to the neat sample did not appreciably increase the protonated analyte signal nor the total ion current for any of the samples analyzed. This observation together with the extremely low pKa values of these pesticides, calculated by SPARC, indicates that the protonated analytes are formed in the gas rather than in the condensed phase. Sodium and ammonium ions were added to these pesticides but in no case was the total ion current increased over that from the neat sample. Solvent studies showed that 50/50 mixtures of methanol/water and acetonitrile/water are both suitable solvent systems but that a methanol fraction of 30% appears to be ideal for some of the pesticides studied. Evidence of radical cation formation was observed when pure acetonitrile was used. It was demonstrated, by spiking 5 carbamate pesticides into Yellowstone River water, that ESI/MS by the direct injection method is a potential candidate as a rapid screening method for pesticides in natural waters.
- Research Organization:
- Montana State Univ., Bozeman, MT (United States)
- OSTI ID:
- 6980714
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400102 -- Chemical & Spectral Procedures
400201* -- Chemical & Physicochemical Properties
CONSTRUCTION
DESIGN
HERBICIDES
MASS SPECTROMETERS
MASS SPECTROSCOPY
MEASURING INSTRUMENTS
PESTICIDES
RESONANCE IONIZATION MASS SPECTROSCOPY
SPECTROMETERS
SPECTROSCOPY