Solvent and Flow Rate Effects on the Observed Compositional Profiles and the Relative Intensities of Radical and Protonated Species in Atmospheric Pressure Photoionization Mass Spectrometry

Abstract

Sample preparation and instrument parameters have regularly been demonstrated to impact upon the observed results in atmospheric pressure photoionization, mass spectrometry (MS), and analytical techniques in general but may be overlooked when such methods are applied to the characterization of real-world samples. An initial investigation into different solvent systems demonstrated that the inclusion of ethyl acetate inverted the ratio of relative intensities of radical and protonated species (R/P). Design of experiments was performed and indicated that the injection flow rate is also a significant factor. The impact of the solvent system and flow rate on signal intensity, the observed compositional profile, and R/P of selected molecular groups is demonstrated further. An inversion of R/P is observed at higher flow rates in solvent systems commonly used in petroleomics studies, effecting a loss of molecular speciation. The findings presented reiterate the critical importance in considering experimental parameters when interpreting the results of analytical procedures.

Semiquantitative Molecular Characterization of Crude Oil

“…20,58 Recently, Mark Barrow's research group proposed an optimization method of APPI analysis by regulating the solvent and solvent flow rate. 59 If the problems of ionization discrimination and production of multiple ion types are effectively solved in the future, then, APPI is a promising approach for the analysis of aromatic hydrocarbons and sulfur-containing compounds in petroleum. In addition, different types of sulfur-containing compounds can be further separated by chemical derivatization and solid phase extractioin (SPE) methods, such as the methylation− demethylation method or silver cation ligand exchange separation, and respectively analyzed and quantified.…”

“…For example, sulfur-containing compounds could be converted into strong polar methyl-sulfoniums by the methylation reaction; aromatic hydrocarbons were subjected to the sulfonation reaction and selectively converted into strong polar sulfonates; saturated hydrocarbons (branched and cyclic alkanes) were converted into alcohols by RICO. These derivatives were then subjected to ESI HRMS analysis, and detailed chemical reaction processes could be found in our previous reports. ,,, APPI is often used to analyze aromatic hydrocarbons and sulfur-containing compounds, but previous studies have shown that it has an ionization inhibition effect on low-condensed monocyclic aromatics and low-condensed thiopheneic compounds or sulfidic compounds. ,, In addition, APPI ionization will produce more than one ion species, such as radical ion and protonated ion, which will hinder the quantitative processing of data. , Recently, Mark Barrow’s research group proposed an optimization method of APPI analysis by regulating the solvent and solvent flow rate . If the problems of ionization discrimination and production of multiple ion types are effectively solved in the future, then, APPI is a promising approach for the analysis of aromatic hydrocarbons and sulfur-containing compounds in petroleum.…”

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

“… , The way of sample introduction, either in solution or as gaseous phase, has an influence on the ionization pathway. In liquid introduction, the solvent type or sample matrix can affect the ionization process by intermolecular interactions. , Solvents, which act as dopants can increase a method’s sensitivity, whereas in other cases, the solvent or the sample matrix decreases the intensity or even completely suppresses the ionization of certain analytes. ,− For photon-based API techniques, light absorption by solvent molecules as well as the solvent flow rate play a role in sensitivity aspects. ,, Gaseous sample introduction by spatial separation of the vaporization and ionization process, for example, by gas chromatography (GC) − or ion mobility spectrometry (IMS), can reduce ion molecule-reactions or solvent/matrix effects. Nonetheless, despite of the separation, both ion types are typically present especially in complex mixtures, where coeluted analytes might interact with each other.…”

“…In liquid introduction, the solvent type or sample matrix can affect the ionization process by intermolecular interactions. 30,31 Solvents, which act as dopants can increase a method's sensitivity, 32 whereas in other cases, the solvent or the sample matrix decreases the intensity or even completely suppresses the ionization of certain analytes. 17,33−36 For photon-based API techniques, light absorption by solvent molecules as well as the solvent flow rate play a role in sensitivity aspects.…”

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

“…In liquid introduction, the solvent type or sample matrix can affect the ionisation process by intermolecular interactions. 25,26 Solvents, which act as dopant can increase a method's sensitivity 27 , whereas in other cases, the solvent or the sample matrix decrease the intensity or even completely suppress the ionisation of certain analytes. 14,28 For photon-based API techniques, light absorption by solvent molecules as well as the solvent flow rate plays a role in sensitivity aspects.…”