Electrospray/VUV single-photon ionization mass spectrometry for the analysis of organic compounds

Abstract

For the comprehensive analysis of organic compounds, especially thermal labile and nonpolar compounds, an electrospray/vacuum ultraviolet (VUV) single-photon ionization (ES-SPI) method was developed. The fine droplets of the sample solution from the electrospray process were directed through a quartz capillary and two skimmers to form a molecular beam into a high vacuum ionization chamber. The neutral sample molecules were softly ionized with tunable VUV light and analyzed with a reflection time-of-flight mass spectrometer (RTOF-MS). The ionization energy (IE) and appearance onsets of fragments were obtained based on the photoionization efficiency (PIE) spectrum. The isomers can also be distinguished. With this new method, clean (fragment-free) mass spectra of nonpolar compounds, such as benzene, cyclohexane, and some thermal labile solid compounds (triphenylamine, thioacetamide, and urea) have been obtained without any tedious pretreatment. The components of complex mixtures (gasoline and kerosene) can be identified. Furthermore, quantitative analysis of the components can be obtained based on photoionization cross section data. This method may be used for quantitative analysis of small biomolecules and natural products. (J Am Soc Mass Spectrom 2009, 20, 430 -434)

Tunable single-photon ionization TOF mass spectrometry using laser-produced plasma as the table-top VUV light source

“…The energy scale in Figure 4 was calibrated using the onset of the PIE spectrum of the naphthalene and diethyl ether ions. The arrows indicate the photon energy corresponding to the ionization potentials of the com- Figure 4a, shows an onset at 8.8 eV and a slow rise up to 10 eV, in agreement with literature data (see Figure 5 of [6] and Figure 2 of [17]). Figure 4b shows the PIE spectrum of C 8 H 10 (106 u), interpreted as the contribution of four isomers of aromatic compounds, m, p, o-dimethylbenzene, and ethylbenzene, at different concentrations.…”

“…Such an approach can allow acquisition of the photo-ionization efficiency (PIE) spectrum for each compound, thereby providing the potential to discriminate isomers with different IPs. The method has proven to be very powerful in many experiments using tunable VUV synchrotron light sources at large-scale facilities [3][4][5][6]. Unfortunately, while synchrotron light sources can provide the tunability and VUV photons needed for "soft" photoionization, they are obviously unfit for on-site and in situ application.…”

Enabling liquid vapor analysis using synchrotron VUV single photon ionization mass spectrometry with a microfluidic interface

“…3 However, liquids have not been often used thus far in single photon ionization mass spectrometry (SPI-MS) applications, because some of them are highly volatile and difficult to retain in vacuum; for a successful VUV SPI-MS measurement, the main chamber vacuum 2 is preferably maintained at 10 -7 Torr. 11,12 Thus, SPI-MS as a vacuum technique has been traditionally restricted to measurements of solid and gas phase samples or liquids with very low volatility such as some ionic liquids.…”

Rapid Identification and Quantification of Linear Olefin Isomers by Online Ozonolysis-Single Photon Ionization Time-of-Flight Mass Spectrometry

“…Single photon ionization (SPI) is another attractive soft ionization technique because of its low degree of fragmentation with simple spectrum interpretation compared with conventional EI method [26,27], especially for complex samples (e.g., gasoline and diesel [28,29], cigarette smoke [30], and volatile organic compounds (VOCs) [31][32][33]). The coupling of SPI with time-of-flight mass spectrometer (SPI-TOFMS) has the advantages of both rapid detection speed and simple spectra analysis [34,35].…”