[Development of a chemical ionization time-of-flight mass spectrometer for continuous measurements of atmospheric hydroxyl radical].

A home-made chemical ionization time-of-flight mass spectrometer (TOFMS) has been developed for continuous measurements of atmospheric hydroxyl radical. Based on the atmospheric pressure chemical ionization technique, an ionization source with orthogonal dual tube structure was adopted in the instrument, which minimized the interference between the reagent gas ionization and the titration reaction. A 63Ni radioactive source was fixed inside one of the orthogonal tubes to generate reactant ion of NO(-)(3) from HNO3 vapor. Hydroxyl radical was first titrated by excess SO2 to form equivalent concentrations of H2SO4 in the other orthogonal tube, and then reacted with NO(-)(3) ions in the chemical ionization chamber, leading to HSO(-)(4) formation. The concentration of atmospheric hydroxyl radical can be directly calculated by measuring the intensities of the HSOj product ions and the NO(-)(3) reactant ions. The analytical capability of the instrument was demonstrated by measuring hydroxyl radical in laboratory air, and the concentration of the hydroxyl radical in the investigated air was calculated to be 1.6 x 106 molecules*cm ', based on 5 seconds integration. The results have shown that the instrument is competent for in situ continuous measurements of atmospheric trace radical.

[Real-time analysis of polyvinyl chloride thermal decomposition/combustion products with single photon ionization/photoelectron ionization online mass spectrometer].

With the features of a broad range of ionizable compounds, reduced fragments and simple mass spectrum, a homemade magnetic field enhanced photoelectron ionization (MEPEI) source combined with single photon ionization (SPI) for time-of-flight mass spectrometer was built and applied to analyze thermal decomposition/combustion products of polyvinyl chloride (PVC). The combined ion source can be switched very fast between SPI mode and SPI-MEPEI mode for detecting different targeted compounds, and only adjusting the voltage of the electrode in the ionization region to trigger the switch. Among the PVC thermal decomposition/combustion products, HCl and CO2, which ionization energies (12.74 eV, 13.77 eV respectively) were higher than the energy of photon (10.60 eV), were ionized by MEPEI, while alkenes, dichloroethylene, benzene and its homologs, monochlorobenzene, styrene, indane, naphthalene and its homologs were ionized by SPI and MEPEI simultaneously. Spectra of interested products as a function of temperatures indicated that products are formed via two main mechanisms: (1) dechlorination and intramolecular cyclization can lead to the formation of HCl, benzene and naphthalene at 250-370 degrees C; (2) intermolecular crosslinking leads to the formation of alkyl aromatics such as toluene and xylene/ethylbenzene at 380-510 degrees C. The experimental results show that the combined ion source of SPI/ SPI-MEPEI for TOF-MS has broad application prospects in the online analysis field.

[Automatic continuous monitoring of volatile organic compounds using ion mobility spectrometer array].

An ion mobility spectrometer array was designed, in order to broaden the detection range of ion mobility spectrometer and improve the accuracy of compound identification. This instrument was based on the combination of ionization sources of 63Ni positive ion mode, 63Ni negative ion mode and photoionization mode with vacuum UV lamp, and it can continuously monitor the volatile organic compounds in air. With the automatic system of sampling and injection of this instrument, the positive ion of dimethyl sulfoxide and negative ion of dichloromethane were detected simultaneously. By comprehensive analysis of spectra with ion mobility spectrometer array, acrylonitrile, m-xylene and acetone were identified, which were difficult to be distinguished under the 63Ni positive ion mode. Acetone samples were determined quantitatively within four days continuously, and the results indicated that the linear range of acetone in this instrument was 2 orders of magnitude. The linear correlation coefficient R was higher than 0.995, and the relative standard deviations were controlled in the range of 4.0%-18.3%. Methacrylate leaked in simulation was monitored on-line for 24 h continuously, using the method of dynamic tracking, and the result showed the leaking time and the concentration of methacrylate directly.

[Development of a membrane inlet-single photon ionization/chemical ionization-mass spectrometer for online analysis of VOCs in water].

A home-made membrane inlet- single photon ionization/chemical ionization- time-of-flight mass spectrometer has been described. A vacuum ultraviolet (VUV) lamp with photon energy of 10.6 eV was used as the light source for single photon ionization (SPI). Chemical ionization (CI) was achieved through ion-molecule reactions with O2- reactant ions generated by photoelectron ionization. The two ionization modes could be rapidly switched by adjusting electric field in the ionization region within 2 s. Membrane inlet system used for rapid enrichment of volatile organic compounds (VOCs) in water was constructed by using a polydimethylsiloxane (PDMS) membrane with a thickness of 50 microm. A purge gas was added to accelerate desorption of analytes from the membrane surface. The purge gas could also help to prevent the pump oil back-streaming into the ionization region from the analyzer chamber and improve the signal to noise ratio (S/N). Achieved detection limits were 2 microg x L(-1) for methyl tert-butyl ether (MTBE) in SPI mode and 1 microg x L(-1) for chloroform in SPI-CI mode within 10 s analysis time, respectively. The instrument has been successfully applied to the rapid analysis of MTBE in simulated underground water nearby petrol station and VOCs in disinfected drinking water. The results indicate that the instrument has a great application prospect for online analysis of VOCs in water.

[Synthesis, characterization and photo degradation application for dye-rhodamine B of nano-iron oxide/bentonite].

The iron oxide/bentonite was prepared through a reaction of a solution of OH-Fe salt with bentonite clay dispersion. BET, XRD an d HRTEM were used t o study i ts surface area, microstructure, and average particle size. The iron oxide/bentonite nano composite was developed as the heterogeneous catalyst for successful discoloration and mineralization of dye rhodamine B And the effects of solution pH, H2O2 molar concentration, catalyst loading and initial rhodamine B concentration were studied in detail by photometric method. The process of degradation was traced by UV-Visible spectrum. Besides, the comparison between the heterogeneous photo-Fenton process and homogeneous photo-Fenton process was performed. The result shows that, it has large surface area and mainly consists of high catalytic activity alpha-Fe2O3. The discoloration ratio is up to 97% and the COD(Cr), removal ratio is 71% after 4 h in the presence of pH 3.0, 2.5 x 10(-5) mol x L(-1) rhodamine B 100 mL, 0.3 g x L(-1) catalyst, 10 mmol x L(-1) H2O2 and UV. The rhodamine B degradating speed of heterogeneous photo-Fenton process is much faster than that of homogeneous photo-Fenton process. The catalyst can be reused after being treated.