High Resolution GC-MSMS
In 2015, Mass Spec Lab added to its instrumental portfolio a powerful new “soft” ionization Atmospheric Pressure Gas Chromatography (APGC) interface at the front end of its quadrupole time-of-flight (QTof) mass spectrometer. The APGC interface includes a 7890 Agilent gas chromatograph and an APGC source. The APGC source is comprised of a heated line, an atmospheric pressure ionization (API) corona pin, and sample cone. Together these function to transport and focus the GC column eluent into the ionizing region around the API corona pin and finally direct the ion stream into the high vacuum ion optics of the Tof. Unlike traditional GC-MS platforms, ion formation in APGC occurs at atmospheric pressure in nitrogen gas and affords “soft” ionization yielding primarily molecular ions with minimal in-source fragmentation. The combination of APGC “soft” ionization with the sensitivity and mass accuracy of the high resolution QTof instrument affords analyte detection limits in the low parts per billion (ppb) and analyte mass accuracies in the low ppm.
Data with the precision and accuracy afforded by Tof detection are unattainable with conventional unit resolution GC-MS analyzers (e.g., single quadrupole instruments). Nonetheless, unit resolution GC-MS analyzers are used for the bulk of most standard volatile and semi-volatile analyses even though their unit mass accuracy makes it impossible to narrow down chemical formula candidates for an analyte to a practical number. Chemical identification with unit resolution mass analyzers depends almost entirely on mass spectral matching to 70eV electron ionization (EI) fragment libraries such as NIST and the WileyRegisty. Hence, if the mass spectrum of an analyte of interest is not present in these libraries then chemical identification is typically unachievable. Unfortunately, the mass spectra of many volatile compounds are not found in these fragment libraries, especially degradants, contaminants and by-products. With the mass accuracy of APGC QTof it is possible to narrow down any volatile analyte’s candidate chemical formulas to a short list that can ultimately lead to unambiguous identification.