A fast detection method to analyze gaseous organic compounds in complex gas mixtures was developed, using a needle trap device (NTD) in conjunction with thermal-desorption photoionization time-of-flight mass spectrometry (TD-PI-TOFMS). The mass spectrometer was coupled via a deactivated fused silica capillary to an injector of a gas chromatograph. In the hot injector, the analytes collected on the NTD were thermally desorbed and directly transferred to the PI-TOFMS ion source. The molecules are softly ionized either by single photon ionization (SPI, 118 nm) or by resonance enhanced multiphoton ionization (REMPI, 266 nm), and the molecular ion signals are detected in the TOF mass analyzer. Analyte desorption and the subsequent PI-TOFMS detection step only lasts ten seconds. The specific selectivity of REMPI (i.e., aromatic compounds) and universal ionization characteristics render PI-MS as a promising detection system. As a first demonstrative application, the alveolar phase breath gas of healthy, nonsmoking subjects was sampled on NTDs. While smaller organic compounds such as acetone, acetaldehyde, isoprene, or cysteamine can be detected in the breath gas with SPI, REMPI depicts the aromatic substances phenol and indole at 266 nm. In the breath gas of a healthy, smoking male subject, several xenobiotic substances such as benzene, toluene, styrene, and ethylbenzene can be found as well. Furthermore, the NTD-REMPI-TOFMS setup was tested for breath gas taken from a mechanically ventilated pig under continuous intravenous propofol (2,6-diisopropylphenol, narcotic drug) infusion.
The manuscript demonstrates the successful application of NTD-TD-REMPI-TOFMS for analysis of volatile organic compounds (VOC) in ship diesel engine exhaust.
The photoionization properties of the pharmaceutically relevant substances amantadine, diazepam, dimethyltryptamine, etomidate, ketamine, mescaline, methadone, and propofol were determined. At beamline U125/2-10m-NIM of the BESSY II synchrotron facility (Berlin, Germany) vacuum ultraviolet (VUV) photoionization spectra were recorded in the energy range 7.1 to 11.9 eV (174.6 to 104.2 nm), showing the hitherto unknown ionization energies and fragmentation appearance energies of the compounds under investigation. Furthermore, (1+1)-resonance-enhanced multiphoton ionization (REMPI) spectra of selected compounds (amantadine, diazepam, etomidate, ketamine, and propofol) were recorded by a continuous scan in the energy range between 3.6 and 5.7 eV (345 to 218 nm) using a tunable optical parametric oscillator (spectral resolution: 0.1 nm) laser system. The resulting REMPI wavelength spectra of these compounds are discussed and put into context with already known UV absorption data. Time-of-flight mass spectrometry was used for ion detection in both experiments. Finally, the implications of the obtained physical-chemical results for potential analytical applications are discussed. In this context, fast detection approaches for the considered compounds from breath gas using photoionization mass spectrometry and a rapid pre-concentration step (e.g., needle trap device) are of interest.
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