Study On Sample Pretreatment Techniques In Single Photon Ionization-Time Of Flight Mass Spectroscopic Analysis Of Volatile Organic Compounds

Portable-single photoionization-time of flight mass spectrometry (SPI-TOFMS) was rapidly developed for online determination of Volatile Organic Compounds in water and air. Growing interest in the development and optimization of sample preconcentration techniques has resulted into intensive research as the traditional sample preparation technologies are complex and time-consuming.Firstly, we presented a new online derivatization and membrane introduction method for rapid determination of phenols in waste water. Membrane Inlet Mass Spectrometer (MIMS) is especially useful for rapid determination of organic compounds in water. Poly-dimethylsilane(PDMS) as the most commonly used membrane material shows low sensitivity for phenols. In this work, a new method of on-line derivatization are presented for high sensitive, rapid determination of 4 phenols (phenol, 3-Methylphenol, 2-Chlorophenol, 2,4-Dichlorophenol) in aqueous solutions by home-made Membrane Inlet-Vacuum ultraviolet(VUV) Ionization-Time of Flight Mass Spectrometer(TOFMS). The detection limits of phenol, 3-Methylphenol, 2-Chlorophenol, 2,4-Dichlorophenol were 3,6,8,14μgL-1 respectively after on-line acetylation, that is satisfactory for the Class A of Integrated Wastewater Discharge Standard (GB 8978-1996). Linear ranges two orders and the analysis time of individual sample less than 15min can be achieved. The soft ionization technique (Single-photon ionization, SPI) using vacuum ultraviolet (VUV) lamp was applied to remove water background effectively, and the fragment-free spectrum is beneficial to analysis. This instrument and method show a certain potential applications to detect phenols in-suit rapidly.Besides, the instrument also could use for online monitoring the reaction of organic compounds to get the information such as intermediate products, the reaction rates and the conversion rates, et al. It provides a possible method for real-time monitoring the chemistry reactions. Secondly, we developed a portable-GC as the injection system of MS to separate and detect VOCs in air.The VUV lamp soft ionization source with low ionization energy, few of fragment ionization was used by MS. The qualitative and quantitative research was depended on the molecular ion peaks which could not accurately discriminate the isomerizes in complex samples. GC is a technique with the ability of high-efficiency separation. Combined with MS, it contained the characteristics of the both devices, and could realize the qualitative and quantitative research of unknown complex compounds. Consequently, a portable GC was constructed. Gaseous samples were adsorbed onto a sorbent trap containing Tenax, then rapidly liberation into GC-MS system by thermal desorption. The detection limits of target samples achieved as high as ppb. New fast-heating device for Chromatographic column and photoionization detector were developed. A self-cleaning system included in could prevent the sensitivity decreased as the electrodes and window of VUV lamp contaminated. The proposed device with MS proved to be promising as a rapid analytical tool for detecting of VOCs in air.