RESUMEN
Reduced sulfur compounds ( RSCs) are one of the main pollutant species in the atmosphere, so it is of great significance to develop a rapid and on-line approaches for their detection. In this study, a portable time-of-flight mass spectrometer ( TOF-MS) with magnetic field enhanced photoelectron ionization source was designed to detect RSCs. The photoelectron ionization source was induced from vacuum ultraviolet photons which generated from vacuum ultraviolet (VUV) lamp with energy of 10. 6 eV. The energy of photoelectrons was controlled by adjusting the extraction voltage to produce the photoelectron ionization, and an annular magnet was used in the ionization region to improve the ionization efficiency of photoelectrons. From the simulation result by SIMION software, it was found that the introduction of magnet field made the motion trajectroies of electrons in the helical motion increase and the convergence of electron at the ionization source was achieved. Experimental results showed that after introducing the magnet filed, the sensitivity of H2 S, SO2 and CS2 was improved by a factor of 5. 3, 9. 4 and 6. 9, respectively. With a detection time of 50 s, the limits of detection for H2S, SO2 and CS2 were 0. 14, 0. 52 and 0. 31 mg/m3(S/N=3), respectively. It could be concluded that the portable TOF-MS with magnetic field enhanced photoelectron ionization source has great potential to be applied for on-line monitoring of volatile sulfides at the emission source.
RESUMEN
A new method was established for the direct, rapid and quantitative analysis of pesticide residues, dimethoate chlorothalonil and malathion by low temperature plasma ( LTP) ionization miniature ion trap mass spectrometer. The LTP ionization probe and sample inlet of ion trap mass spectrometry were enclosed in a metal cavity. With non-contact heating, the samples placed on the sample platform were desorbed into gaseous phase and ionized by LTP ionization probe. The results showed that closed ionization had an edge over the opened ionization. The quantitative analysis of 3 pesticides within the range of 0. 5-10 mg/L was realized by optimizing heating time and flow rate of air, and the relative standard deviations of signal intensity is less than 11%. LODs of pesticide, which were obtained within 5 s, were as low as several hundred pictograms. The results showed that the method could be used for the analysis of pesticide residue on green and organic fruits or vegetables.