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.
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.
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 H2S, 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/m(3)(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.
The productions of multiply charged ions in the interactions of intense nanosecond laser pulse with clusters have aroused broad interests in molecular physics. Benzene, cyclohexene and cyclohexane clusters are chosen to study the effect of multiphoton ionization (MPI) efficiency on the relative intensity of multiply charged ions, as they possess similar molecular structures and the same element constitutions. They are ionized with a 5 ns Nd-YAG nanosecond laser. The carbon charge state produced by cyclohexene and cyclohexane is about 4; while by benzene is only about 3. The ratios of C3+/C2+ for cyclohexane, cyclohexene and benzene are 1.1, 0.6 and 0.4, respectively. The relative MPI efficiencies of three molecules are measured to be in the magnitude sequence of benzene > cyclohexene > cyclohenane by diffusion beam. Higher MPI efficiency of molecules can cause more than one molecules to be ionized at the edge of laser pulse, the Coulomb repelling force between adjacent ions leads clusters to early split into small size ones, which will prevent the production of the highly charged ions.
The production of multiply charged ions by the interaction of intense femtosecond laser with clusters has been widely reported. Recently, many groups discovered the multiply charged ions when the cluster was irradiated by a 532 nm nanosecond laser with the intensity as low as 1010 W/cm2. Although this interesting phenomenon could be explained by the mechanism of multiphoton ionization triggered-inverse bremsstrahlung heating-electron impact ionization, there is a lack of numerical simulation to explain the generation of multiply charged ions. In this paper, numerical simulation is performed to study the generation process of multiply charged ions in the moderate intensity laser. Firstly, the electron energy is calculated according to ponderomotive potential. Secondly, the cross section of electron impact ionization is calculated on the basis of Lotz formula. Finally, the evolution of multiply charged ions in the cluster is calculated with the kinetic reaction rate equation. The effects of cluster size and electron density on multiply charged ions are investigated in detail. Simulation results show that the ionization process is completed and the balance among C2+, C3+ and C4+ is achieved in 0.7 ns. The relative intensity sequence of multiply charged ions is C2+ C3+ C4+, which is consistent with the experimental results. In addition, numerical simulation results show that the charge state of ions is increased with the increase of cluster size, which is consistent with the experimental results.
The excessive flavorings in food are a growing public health concern, particularly in foods for infants and children. A rapid and simple method for simultaneous detection of multiple flavorings in food is urgently needed. In this work, a method with direct analysis in real time-mass spectrometry has been developed and applied to the simultaneous determination of four flavorings, including maltol, ethyl maltol, vanillin, and ethyl vanillin. The ionization efficiency of flavor compounds in the quantitatively-dip-it probe mode was compared with that in the quick strip mode, which revealed that a solvent-assisted ionization mechanism might be involved in the ionization process. The developed method showed good linearity (R2 > 0.99) in the range from 5 to 1000 μg L−1, sensitivity (LODs <3.3 μg L−1), recoveries (84.8%–96.9%), satisfactory repeatability (RSD <14.3%, n = 5), and high-throughout (12 infant formula samples completed in 15 min). The LOQs (0.55–1.1 mg kg−1) for the infant formula sample were much lower than the regulatory limits. The developed method provided an alternative way to monitor the excessive addition of flavorings.
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