Development of a Portable Single Photon Ionization-Photoelectron Ionization Time-of-Flight Mass Spectrometer

A vacuum ultraviolet lamp based single photon ionization- (SPI-) photoelectron ionization (PEI) portable reflecting time-of-flight mass spectrometer (TOFMS) was designed for online monitoring gas samples. It has a dual mode ionization source: SPI for analyte with ionization energy (IE) below 10.6 eV and PEI for IE higher than 10.6 eV. Two kinds of sampling inlets, a capillary inlet and a membrane inlet, are utilized for high concentration and trace volatile organic compounds, respectively. A mass resolution of 1100 at m/z 64 has been obtained with a total size of 40 × 31 × 29 cm, the weight is 27 kg, and the power consumption is only 70 W. A mixture of benzene, toluene, and xylene (BTX), SO2, and discharging products of SF6 were used to test its performance, and the result showed that the limit of quantitation for BTX is as low as 5 ppbv (S/N = 10 : 1) with linear dynamic ranges greater than four orders of magnitude. The portable TOFMS was also evaluated by analyzing volatile organic compounds from wine and decomposition products of SF6 inside of a gas-insulated switchgear

Dopant-assisted reactive low temperature plasma probe for sensitive and specific detection of explosives

A dopant-assisted reactive low temperature plasma (DARLTP) probe was developed for sensitive and specific detection of explosives by a miniature rectilinear ion trap mass spectrometer. The DARLTP probe was fabricated using a T-shaped quartz tube. The dopant gas was introduced into the plasma stream through a side-tube. Using CH2Cl2 doped wet air as the dopant gas, the detection sensitivities were improved about 4-fold (RDX), 4-fold (PETN), and 3-fold (tetryl) compared with those obtained using the conventional LTP. Furthermore, the formation of [M + Cl-35](-) and [M + Cl-37](-) for these explosives enhanced the specificity for their identification. Additionally, the quantities of fragment ions of tetryl and adduct ions such as [RDX + NO2](-) and [PETN + NO2](-) were dramatically reduced, which simplified the mass spectra and avoided the overlap of mass peaks for different explosives. The sensitivity improvement may be attributed to the increased intensity of reactant ion [HNO3 + NO3](-), which was enhanced 4-fold after the introduction of dopant gas. The limits of detection (LODs) for RDX, tetryl, and PETN were down to 3, 6, and 10 pg, respectively. Finally, an explosive mixture was successfully analyzed, demonstrating the potential of the DARLTP probe for qualitative and quantitative analysis of complicated explosives

Application of LIBS technology to the rapid measure of heavy metal contamination in soils

Laser-induced breakdown spectroscopy(LIBS) has emerged in the past ten years as a promising technique for analysis and measure. The fundamental principle of LIBS for in situ qualitative and quantitative analysis is introduced. Current development of the instrument and its applications in rapid detection of heavy metal contamination elements, such as As, Cd, Cr, Hg, Pb and Zn in soils are reviewed in detail. The critical problems such as how to achieve quantitative measurement and improve the detection limit of LIBS are discussed

Dependence of multiply charged ions on the polarization state in nanosecond laser-benzene cluster interaction

This paper investigated the dependence of multiply charged ions on the laser polarization state when benzene cluster was irradiated with 532 and 1064 nm nanosecond laser. A circle, square and flower distribution for C2+, C3+ and C4+ were observed with 532 nm laser respectively, while flower petals for C2+, C3+ and C4+ were observed at 1064 nm as the laser polarization varied. A theoretical calculation was performed to interpret the polarization state and wavelength dependence of the multiply charged ions. The simulated results agreed well with the experimental observation with considering the contribution from the cluster disintegration. (C) 2016 Elsevier B.V. All rights reserved

Ambient temperature nanoelectrospray ion mobility detector for high performance liquid chromatography in determining amines

A nanoelectrospray ionization ion mobility spectrometer (nanoESI-IMS) working at ambient pressure and ambient temperature was developed as a detector of high performance liquid chromatography (HPLC) to achieve sensitive detection of amines with no derivatization and meanwhile provide another dimension of separation. The easier desolvation property of the charged droplets formed in nanoESI source enabled complete desolvation of the product ions of sixteen amines and drugs using the nanoESI-IMS at ambient temperature. Working at ambient temperature was good for suppressing the dissociation of thermal volatile ions, such as only the proton adducted molecular ions were observed for morphine in the nanoESI-IMS. Besides, the resolving power of the nanoESI-IMS also showed an increasing tendency as lowering the working temperature, an increment of 19 percent and 10 percent was observed for diethylamine and triethylamine as the temperature dropped from 92 degrees C to 32 degrees C. The resolving power of the nanoESI-IMS at 32 C for the 16 tested compounds was amid 33-44. With the nanoESI-IMS coupled to HPLC, a six-compound mixture including isomers was successfully separated and detected without any derivatization. And linear response ranges of 1 to 20, 0.5 to 20, and 0.8 to 20 mu g ml(-1) and limits of detection of 0.25, 0.15, and 0.17 mu g ml(-1) for triethylamine, diethylamine, and butylamine, respectively, were obtained with the hyphenated system. These results showed the excellent performance of the two-dimensional separation and detection method in direct qualitative and quantitative analyses of amines. (C) 2014 Elsevier B.V. All rights reserved

An in-source helical membrane inlet single photon ionization time-of-flight mass spectrometer for automatic monitoring of trace VOCs in water

An in-source, helical membrane inlet single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) has been developed to improve the detection sensitivity of trace volatile organic compounds (VOCs) in water. A helical winding membrane and a four-stage differential pumping system of TOFMS was designed to improve and maintain the vapor pressure of analyte, which is linearly associated with the sensitivity of SPI. The helical winding increased the length of the hollow fiber membrane (HFM) from 7 cm to 100 cm and the pressure inside of SPI source was elevated from 3.6 Pa to 28 Pa, and then the sensitivity was increased by 16, 34.7, 32.3, 17.9 and 13.9 times for benzene, ethyl tert-butyl ether (ETBE), aniline, p-xylene, and chlorobenzene (MCBz) respectively. The limits of quantitation (LOQs) of benzene, ETBE, aniline, p-xylene and MCBz were 0.014, 0.143, 0.556, 0.036, 0.025 mu g L-1 respectively with a measurement time of 50 s, which were enhanced by more than one order of magnitude compared to our previous work (reference [32]). The in-source design of helical winding membrane i.e. putting the membrane inside the SPI source dramatically reduced the response time to 1.33 min. This system has been evaluated for VOCs in sewage water of different laboratory buildings and automatic monitoring the pollutants in sewage water from a biological laboratory building. The automatic continuous analysis of organic pollutants in water has very important significance and broad application prospect for online assessment of water quality

Development and Application of a Chemical Ionization Focusing Integrated Ionization Source TOFMS for Online Detection of OVOCs in the Atmosphere

Single photon ionization (SPI) based on vacuum ultraviolet (VUV) lamps has been extensively investigated and applied due to its clean mass spectra as a soft ionization method. However, the photon energy of 10.6 eV and photon flux of 1011 photons s−1 of a commercial VUV lamp limits its range of ionizable analytes as well as its sensitivity. This work designs a chemical ionization focusing integrated (CIFI) ionization source time-of-flight mass spectrometry (TOFMS) based on a VUV lamp for the detection of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs). The photoelectrons obtained from the VUV lamp via the photoelectric effect ionized the oxygen and water in the air to obtain the reagent ions. The ion–molecule-reaction region (IMR) is constituted by a segmented quadrupole that radially focuses the ions using a radio-frequency electric field. This significantly enhances the yield and transport efficiency of the product ions leading to a great improvement in sensitivity. As a result, a 44-fold and 1154-fold increase in the signal response for benzene and pentanal were achieved, respectively. To verify the reliability of the ionization source, the linear correspondence and repeatability of benzene and pentanal were investigated. Satisfactory dynamic linearity was obtained in the mixing ratio range of 5–50 ppbv, and the relative standard deviation (RSD) of inter-day reached 3.91% and 6.26%, respectively. Finally, the CIFI−TOFMS was applied to the determination of OVOCs, and the LOD of 12 types of OVOCs reached the pptv level, indicating that the ionization source has the potential for accurate and sensitive online monitoring of atmospheric OVOCs