Mass spectrometry is a desirable detector in analytical chemistry due to its powerful combination of sensitivity and selectivity owing to the often unambiguous characteristic of mass:charge ratio (m/z) of molecular ions and patterns of fragmentation during MS/MS experiments. Primary NPASR equipment includes three liquid chromatography/photodiode array/tandem mass spectrometry systems:
Quattro Ultima: a triple quadrupole suited to quantitative analyses supported by an Acquity ultra high pressure liquid chromatography (UPLC). Triple quadrupole instruments are rugged and exhibit a large linear dynamic range for quantitative work.
AB Sciex QTrap 5500: a hybrid quadrupole ion trap system coupled with an Agilent 1200 SL/DAD system providing both qualitative and quantitative results. The QTrap can perform MS/MS/MS (MS3) experiments for enhanced identification and selectivity. The Agilent 1,200 is one of two in house chromatographic systems which operate at pressures in excess of 10,000 psi with sub-2 micron particle columns, allowing for rapid separations and enhanced sensitivity, owing to higher resolution than conventional HPLC.
QTof Premier: a quadrupole time-of-flight instrument coupled with an Alliance HPLC/PDA for metabolite screening and identification. Time-of-flight analyzers provide high mass resolution (up to 20,000) and accurate mass capabilities (1-2 ppm) for identification.
Our mass spectrometers can be operated in electrospray or atmospheric pressure chemical ionization (APcI) mode, the former more suitable for polar compounds and the latter for lipophilic compounds. This allows us to study a broad range of compounds from water-soluble nutrients to lipophilic phytochemicals. The combination of chromatography, PDA and MS detection allows for a unique set of characteristics – elution time, UV-vis spectrum and molecular weight/fragmentation pattern – that provide a high degree of confidence in the proper identification of a compound while avoiding interferences.
Accurate mass information (QTof) can reduce the list of potential chemical formulas for an unknown. In addition, metabolomics software can be applied to sift through MS screening data sets to find characteristic product ions and neutral losses that help identify compounds with certain modifications as well as quickly compare baseline and control samples for components associated with treatment. Starting with known compounds, algorithms are applied to predict sites for metabolism which also enhances the discovery of metabolites in biological specimens. In addition, authentic standards when available are used to confirm identity and quantify levels.