Gas chromatography/electron capture negative-ion mass spectrometry at the zeptomole level

Abstract

Twelve years ago, Hunt and Crow demonstrated that 20-50-amol amounts of strong electophores could be detected with a Finnigan quadrupole gas chromatograph/electron capture negative-ion mass spectrometer GC/ECNI-MS (1). These measurements were made after the conditions in the instrument were optimized for high sensitivity: electron energy 100 eV, methane reagent gas pressure 0.6-0.8 Torr, and source temperature 100-150 °C. Unremarkably, it would seem, nearly the same conditions are recommended by the manufacturer (Hewlett-Packard) for optimum sensitivity of the quadrupole ECNI-MS that we possess, based on testing the instrument with the prescribed electrophore, octafluoronaphthalene (OFN). However, it has been established that the response in ECNI is subject to many variables, including compound tested, type of instrument, and several parameters of the ion source (2-6). Thus we considered that it was worthwhile to tune our GC/ECNI-MS for the electrophoric analytes of interest in our laboratory. As reported here, such tuning leads to a set of conditions which significantly increase the S/N for these latter types of compounds, but only a little for OFN.

The application of mass spectrometry in molecular dosimetry: Ethylene oxide as an example

“…By monitoring the most-abundant fragment ion, GC/ECNCI-MS SIM analysis of this derivative demonstrated excellent sensitivity and specificity for quantification of N7-HEG (Saha et al, 1989;Allam, Saha, & Giese, 1990). An on-column detection limit of 1.3 amol (1 Â 10 À18 mol) was reported at a signal-to-noise ratio of 13 (Abdel-Baky & Giese, 1991). That method is extremely sensitive for analysis of N7-HEG.…”

“…Another method using pentafluorobenzyl bromide (PFBBr) as a derivatization reagent was also developed (Abdel-Baky & Giese, 1991;Saha, Abushamaa, & Giese, 1995;Giese, 1997). PFBBr is an electrophore that readily attaches to low-energy electrons in the gas phase to stabilize the negative charge to form negative ions (Halket, 1994).…”

“…Among the MS methods for analysis of N7-HEG mentioned above, GC/ECNCI-MS SIM analysis of the PFB-derivatives is the most sensitive with an on-column limit of detection at 1.3 amol of synthetic N7-HEG standard (Abdel-Baky & Giese, 1991). When tissue DNA were prepared and derivatized twice with PFBBr, GC/ECNCI-MS SIM analysis of the PFBBrderivatized N7-HEG showed chromatograms with numerous interferences, making quantification of N7-HEG difficult.…”

A GC–MS/MS method for the quantitative analysis of low levels of the tyrosine metabolites maleylacetone, succinylacetone, and the tyrosine metabolism inhibitor dichloroacetate in biological fluids and tissues

“…Electron capture is a highly sensitive ionization technique and can be used to improve the detection limits of electron ionization (EI) methods [14][15][16]. The use of a derivatizing agent with high electron capture ability and the capacity to provide stable negative ions results in increased sensitivity over positive CI or EI.…”

4-(4′-Methyltetrafluorophenyl)-2,3,5,6-tetrafluorobenzyl bromide: A new electrophoric derivatizing reagent

“…Most notable is the high sensitivity it can provide, reaching the low amol level for standard compounds having high gas phase electron affinity and thermal stability [1][2][3]. Recent applications have been reviewed [4].…”