Huapeng Cui

Single photon ionization and chemical ionization combined ion source based on a vacuum ultraviolet lamp for orthogonal acceleration time-of-flight mass spectrometry.

A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 10(11) photons s(-1), while the CI was achieved through ion-molecule reactions with O(2)(+) reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface.

Vacuum Ultraviolet Lamp Based Magnetic Field Enhanced Photoelectron Ionization and Single Photon Ionization Source for Online Time-of-Flight Mass Spectrometry

A magnetic field enhanced photoelectron ionization (MEPEI) source combined with single photon ionization (SPI) was developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). A commercial radio frequency (rf) powered vacuum ultraviolet (VUV) lamp was used as SPI light source, and the photoelectrons generated by photoelectric effect were accelerated to induce electron ionization (EI). The MEPEI was obtained by applying a magnetic field of about 800 G with a permanent annular magnet. Compared to a nonmagnetic field photoelectron ionization source, the signal intensities for SO(2), SF(6), O(2), and N(2) in MEPEI were improved more than 2 orders with the photoelectron energy around 20 eV, while most of the characteristics of soft ionization still remained. Simulation with SIMION showed that the sensitivity enhancement in MEPEI was ascribed to the increase of the electron moving path and the improvement of the electrons transmission. The limits of detection for SO(2) and benzene were 750 and 80 ppbv within a detection time of 4 s, respectively. The advantages of the source, including broad range of ionizable compounds, reduced fragments, and good sensitivity with low energy MEPEI, were demonstrated by monitoring pyrolysis products of polyvinyl chloride (PVC) and the intermediate products in discharging of the SF(6) gas inpurity.

On-line Analysis of Flavor Compounds in Toothpastes by Single Photon Ionization Mass Spectrometry: On-line Analysis of Flavor Compounds in Toothpastes by Single Photon Ionization Mass Spectrometry

A new method was developed for the on-line analysis of flavor compounds in toothpastes without any sample preparation by direct injection time-of-flight mass spectrometry with single photon ionization (SPI-TOFMS). The samples were directly taken into the ionization source by the quartz capillary tube and the pressure condition of the ionization source was optimized. Under the discrimination of characteristic mass spectra of flavor compounds, rapid and accurate identification of flavors in toothpastes was achieved. The analysis time for a single sample was only 0. 5 min. This method was applied to on-line and in-situ monitoring of flavor compounds during tooth brushing process. The influence of water content on release of flavor compounds from toothpastes was studied. The results indicate that direct injection SPI-TOFMS can monitor the composition and concentration of flavor compounds in real time. The method could be suitable to analyze the flavors from various samples such as food and cosmetics.

Characterization and Applications of Combined Single Photon Ionization and Photoelectron Ionization Source: Characterization and Applications of Combined Single Photon Ionization and Photoelectron Ionization Source

The characters and applications of combined single photon ionization (spi) and photoelectron ionization (pei) source were introduced. the ion source can generate dominated molecular ions in spi mode and fragments ions same as standard el spectrum in pei mode. the switch time between the two modes was several microseconds. the limit of detection in spl mode was reduced by increasing the optical path in the ion source. achieved detection limits were 0. 05 ml/m(3) and 20 ml/m(3) for benzene in spi mode and so(2) in pei mode with accumulating time of 4 s respectively. products in the process for catalytic dehydrogenation of alkanes were monitored in spi mode. in addition, the samples of sf(6) were analyzed in pei mode with low energy electrons and the impurities were identified.