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Direct infusion mass spectrometry (DIMS) is an essential technique for measuring chemicals that form from degradation processes in real time. As an analytical tools for metabolomics and biomarker discovery, it can be used to directly link appearing and disappearing molecules to one another using proper MS monitoring experiments.
It was used in two cases where the analyte products were originally unknown. In the first, mancozeb (MZ), a fungicide was monitored for appearance inside neuronal cultures. The precursor ion could not be measured effectively so ion fragmentation of the parent compound was evaluated using full scan MS, tandem mass (MS2) and triple stage mass spectrometry (MS3). MZ was detectable at levels near 10 nM as measured in the cell lysate. MS, MS2 and MS3 revealed fragmentation ions that were directly related to MZ and could be sued for quantative analysis. Quantitation of cell media and lysate revealed that approximately 7–8% of the original dose crossed the cell membrane and remained stable for approximately 3 h. The parent compound began to decompose and/or metabolize inside the cell but the product was detectable up to 14 h post-treatment.
In the second DIMS experiment, (−)-Epigallocatechin-3-gallate (EGCG) the most abundant and biologically active compound in tea, was monitored for it’s breakdown/oxidation product(s). The stability of EGCG in Tris-HCl buffer was investigated using real-time mass scanning combined with tandem mass ion mapping. An EGCG quinone product, EGCG dimer quinone and other compounds related to autooxidation were observed. They were linked to the original analyte by monitoring the disappearance of the precursor EGCG ion and the autooxidation product ions simultaneously. None of these oxidation products were observed in the plasma samples of treated mice, although they were observed to form in buffer. Metabolomics and biomarker discovery perspectives on these direct infusion MS measurements will be discussed.