Detailed Comparison of Xenon APPI (9.6/8.4 eV), Krypton APPI (10.6/10.0 eV), APCI, and APLI (266 nm) for Gas Chromatography High Resolution Mass Spectrometry of Standards and Complex Mixtures

Abstract

Photoionization schemes for mass spectrometry, either by laser or discharge lamps, have been widely examined and deployed. In this work, the ionization characteristics of a xenon discharge lamp (Xe-APPI, 9.6/8.4 eV) have been studied and compared to established ionization schemes, such as atmospheric pressure chemical ionization, atmospheric pressure photoionization with a krypton discharge lamp (Kr-APPI, 10.6/10 eV) and atmospheric pressure laser ionization (266 nm). Addressing the gas-phase ionization behavior has been realized by gas chromatography coupled to high-resolution mass spectrometry without the usage of a dopant. For standard substances, it has been found that Xe-APPI is able to ionize a broad range of polycyclic aromatic hydrocarbons as well as their heteroatom-containing and alkylated derivatives. However, thiol and ester compounds could not be detected. Moreover, Xe-APPI revealed a high tendency to generate oxygenated artifacts, most likely due to a VUV absorption band of oxygen at 148 nm. Beneficially, almost no chemical background, commonly caused by APCI or Kr-APPI due to column blood, plasticizers or impurities, is observed. This advantage is noteworthy for evolved gas analysis without preseparation or for chromatographic coelution. For the complex mixtures, Xe-APPI revealed the predominant generation of radical cations via direct photoionization with a high selectivity toward aromatic core structures with low alkylation. Interestingly, both Xe-APPI and Kr-APPI could sensitively detect sterane cycloalkanes, validated by gas chromatographic retention. The narrowly ionized chemical space could let Xe-APPI find niche applications, e.g., for strongly contaminated samples to reduce the background.

Accessing the Low-Polar Molecular Composition of Boreal and Arctic Peat-Burning Organic Aerosol via Thermal Analysis and Ultrahigh-Resolution Mass Spectrometry: Structural Motifs and Their Formation

“…The CH class shows, regardless of the peat origin and for both combustion conditions, an intensity maximum at 27–31 carbons and DBE values between 6 and 10. In the literature, a variety of different organic compounds was identified in peat that includes n -alkanes, fatty acids, alcohols, and squalene as well as cyclic compounds such as di- and triterpenoids or steroids. , However, the here observed DBE/#C range fit especially squalene (C 30 H 50 , DBE 6) and its derivatives or sterane-based biomarkers, which can also be ionized by APPI …”

“…Smoldering combustion is known to emit nitrogen-containing compounds from the low-temperature, oxygen-depleted combustion of biomass, and in particular, peat was found to emit high concentrations of, e.g., pyridine-like compounds, which would fit the observed distribution in the DBE versus carbon number plot (Figure b) . The overall number and intensity of nitrogen-containing compounds is low compared to the other classes, which may partially be explained by their lower ionization efficiency in APPI. , …”

Triboelectric Nanogenerators for the Masses: A Low-Cost Do-It-Yourself Pulsed Ion Source for Sample-Limited Applications

“…TENG ion sources use low-voltage power supplies to drive the necessary mechanical motion, with the generated high-voltage electricity presenting little more danger than static shock. As compared to other liquid ionization techniques which also do not require high-voltage power supplies such as atmospheric-pressure photoionization, vibrating sharp-edge spray ionization, and zero-voltage paperspray, TENG is unique in that it can preserve the high sensitivity and other traits associated with nESI when used with standard glass capillary nESI emitters. ,− …”

GC-FTICR mass spectrometry with dopant assisted atmospheric pressure photoionization: application to the characterization of plastic pyrolysis oil

“…24,32,33 To overcome these disadvantages, atmospheric pressure photoionization (APPI) could be used. 34…”