SinS - Abstract

Abstract Information :

Recent shortages of helium and its rising cost have presented challenges for GC/MS laboratories around the world and increased interest in looking for alternative carrier gases. For GC/MS, hydrogen is the best alternative to helium. Among the problems encountered when converting to hydrogen carrier gas is that hydrogen as a reactive gas may lead to spectral infidelity, excessive background, sensitivity loss and decreased precision. LECO has recently introduced a multi-mode ion source, which can generate ions via EI, and Positive or Negative CI. Ions are created in CI through ion-molecular reaction steps. Therefore, the effects of hydrogen carrier gas can be a concern. In this work we report an evaluation of GCxGC-HR-TOFMS with the MMS while using hydrogen carrier gas for non-target screening. The combination of standard (NIST, Wiley, et.) library matching and accurate mass chemical formula confirmation for molecular ions and characteristic fragment ions is an important tool for analyte identification in nontarget screening applications. Having good isotopic and fragmentation pattern fidelity of the mass spectra while using hydrogen as a carrier gas is an essential condition for efficient nontarget analysis. Semi-volatile organic compounds (SVOCs) from US EPA Method 8270 were used to evaluate the performance of the source with respect to peak shape, calibration and spectral fidelity when searched against the NIST spectral library. No peculiarities related to hydrogen carrier gas were detected. The standards were also run using helium as a carrier gas to compare sensitivity, precision, linear dynamic range, and spectral fidelity with the results obtained using hydrogen. Additionally, further analyses, using hydrogen, of several real samples (environmental, food, petroleum, etc), were performed, demonstrating comparable mass spectral performance to that obtained with helium, and in some cases significantly faster chromatographic separations were obtained.