Inborn errors of metabolism (IEM) cause significant morbidity and mortality when left untreated. A strong indicator of IEM-presenting patients are their urine organic acid (UOA) levels, usually qualitatively analyzed via the current gold standard, GC-EI-MS (Gas Chromatography-Electron Impact-Mass Spectroscopy). The Agilent 7890 GC in tandem with the Waters’ Xevo TQ-S MS contains an easily interchangeable LC-ESI (liquid chromatography-electrospray Ionization) and GC-APCI (Atmospheric Pressure Chemical Ionization) instrument set-up, while maintaining accuracy and sensitivity in both LC and GC applications. Chemical standards and patient urine samples were initially spiked with tropic acid, the internal standard. UOAs were then extracted via a liquid-liquid ether extraction and reacted with BSTFA to form trimethylsilyl derivatives. GC-MS was performed in full scan mode with a chromatographic separation over 45 minutes. Initial instrument suitability and method setup was tested and compared on both the current GC-MS and the new APCI-GC-MS. APCI was run in wet mode through methanol or water vials in the source enclosure to induce [M+H]+ ions via the proton transfer mechanism. This mode was found to increase instrument sensitivity and was monitored for instrument stability each run using a 1:1 ratio of 4-bromo-diphenyl-ether and phenanthrene. Individually extracted UOA standards were run to determine retention times and mass spectra profiles. Optimal cone voltages, collision energies, and product ions were determined to develop the multiple reaction monitoring (MRM) mode analysis, further increasing sensitivity. Initial experiments of patient samples and standards achieved adequate separation of UOAs including many isobaric compounds. The Waters’ Xevo TQ-S micro with Agilent 7890 GC demonstrated promising GC-resolution separation of UOA metabolites using APCI-MS detection. Next steps include the expansion of the UOA mass spectra reference library specific for APCI prior to clinical use. With the research progression thus far, this is likely achievable with the potential for future quantitative analysis as well.

Inborn errors of metabolism (IEM) cause significant morbidity and mortality when left untreated. A strong indicator of IEM-presenting patients are their urine organic acid (UOA) levels, usually qualitatively analyzed via the current gold standard, GC-EI-MS (Gas Chromatography-Electron Impact-Mass Spectroscopy). The Agilent 7890 GC in tandem with the Waters’ Xevo TQ-S MS contains an easily interchangeable LC-ESI (liquid chromatography-electrospray Ionization) and GC-APCI (Atmospheric Pressure Chemical Ionization) instrument set-up, while maintaining accuracy and sensitivity in both LC and GC applications. Chemical standards and patient urine samples were initially spiked with tropic acid, the internal standard. UOAs were then extracted via a liquid-liquid ether extraction and reacted with BSTFA to form trimethylsilyl derivatives. GC-MS was performed in full scan mode with a chromatographic separation over 45 minutes. Initial instrument suitability and method setup was tested and compared on both the current GC-MS and the new APCI-GC-MS. APCI was run in wet mode through methanol or water vials in the source enclosure to induce [M+H]^+^ ions via the proton transfer mechanism. This mode was found to increase instrument sensitivity and was monitored for instrument stability each run using a 1:1 ratio of 4-bromo-diphenyl-ether and phenanthrene. Individually extracted UOA standards were run to determine retention times and mass spectra profiles. Optimal cone voltages, collision energies, and product ions were determined to develop the multiple reaction monitoring (MRM) mode analysis, further increasing sensitivity. Initial experiments of patient samples and standards achieved adequate separation of UOAs including many isobaric compounds. The Waters’ Xevo TQ-S micro with Agilent 7890 GC demonstrated promising GC-resolution separation of UOA metabolites using APCI-MS detection. Next steps include the expansion of the UOA mass spectra reference library specific for APCI prior to clinical use. With the research progression thus far, this is likely achievable with the potential for future quantitative analysis as well.

Novel application of atmospheric pressure chemical ionization gas chromatography mass spectroscopy (APCI-GS-MS) for the detection of metabolic urine organic acids in chemical standards and newborn patient samples

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.