Application of Gas Chromatography/Electron Capture Negative Chemical Ionization High-Resolution Mass Spectrometry for Analysis of DNA and Protein Adducts

Abstract

The analytical potential of gas chromatography/electron capture negative chemical ionization high-resolution mass spectrometry (HRMS) for characterization and quantitation of DNA and hemoglobin adducts was demonstrated using three model compounds: N2, 3-ethenoguanine (EG), 7-(2-hydroxyethyl)guanine (7-HEG), and N-(2-hydroxyethyl)valine (HEV). At a resolving power of 10 000, the signal-to-noise (S/N) ratios obtained from quantitative selected ion monitoring (SIM) experiments using biological samples were comparable to or better than existing unit mass resolution experiments due to the reduction of chemical noise from the use of narrower mass windows. The specificity gained by HRMS was essential for quantitation of ultratrace amounts near the limit of detection since coeluting interferences of the analyte or internal standard can lead to inaccurate measurement of response factors. The limit of detection (LOD) was 100 amol (S/N = 5) using a pure standard of TTB2-EG. The LOD for complete assays using spiked samples was 500 amol (S/N = 5) for EG and 600 amol (S/N = 5) injected for 7-HEG. The standard deviation (SD) for the HRMS quantitative measurements was typically less than 10%. The SD for the complete biological assays as determined by spiking replicate samples was less than 15%. This method has adequate sensitivity and specificity to accurately measure DNA and protein adducts as low as endogenous concentrations in rodent and human tissues.

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

“…This demonstrated that the increase in MS resolution power to 10,000 would lead to a narrower mass window to reduce chemical noise and analyte signal simultaneously. But, HRMS analysis still achieved similar or even better sensitivity than the GC/ ECNCI-MS SIM (Ranasinghe et al, 1998). Further studies showed that the derivatization of DNA samples with PFBBr led to the formation of the undesirable interferences, most likely due to the free purine bases released from neutral thermal hydrolysis of DNA (Kao & Giese, 2005).…”

“…To eliminate the noise and to improve the quality of quantification, GC/ECNCI-HRMS with resolution at 10,000 was used to quantify PFPTH-HEV (Ranasinghe et al, 1998). GC/ECNCI-HRMS full-scan analysis of the PFPTH-HEV derivative revealed the two major fragment ions at m/z ¼ 348.0556 (-HF) and m/ z ¼ 318.0450 due to further loss of CH 2 O and m/z ¼ 352.0830 by loss of HF and 320.0573 due to further loss of CD 2 O from the corresponding deuterium-labeled HEV derivative.…”

“…Relative response factors from monitoring additional ions can serve as qualifiers and further provide an important diagnostic value because deviations of relative ion abundances from the expected values usually indicate a coeluting interference. However, monitoring more ions might deteriorate the detection limit (Ranasinghe et al, 1998). The sensitivity of the GC/ECNCI-HRMS method was improved only slightly when compared with GC/ECNCI-MS because the gain in specificity with GC/ECNCI-HRMS is always compensated for by the loss of analyte signal (Table 6).…”

“…It was estimated that ca. 5% of the ion beam remained when the resolution was increased from 1,000 to 10,000 (Ranasinghe et al, 1998). …”

Purification and Recovery of Bulky Hydrophobic DNA Adducts

“…However, nuclear magnetic resonance suffers from a requirement for considerably more sample amount than does MS. MS is especially useful if coupled with a separation scheme such as TLC (28), HPLC (29,30), capillary electrophoresis (CE) (31)(32)(33), capillary electrochromatography (CEC) (34), or gas chromatography (35), although this latter technique usually requires derivatization, which introduces other analysis problems (36). However, when MS monitors only selected ions or reactions, although its sensitivity is considerably enhanced, its identification powers are sharply reduced.…”