Study Of The Membrane Introduction TOF-MS For On-line Analysis Ethers Gasoline Additive In Water

With the strengthen of the people’s consciousness of environment protection，onlinedetermination of Volatile Organic Compounds(VOCs) in water and air was rapidly developed.Although the traditional chromatographic analysis is sensitive and accurate, the samplepreparation technologies are complex and time-consuming. So the online samplepre-concentration technique has been a hot area of research in recent years.This project based on a home-build setup of the magnetic field enhanced single photonionization/photoelectron ionization source time-of-flight mass spectrometer (ME-SPI/PEI-TOF-MS) We developed two membrane inlet apparatus, and combined with ME-SPI/PEI-TOFMS toonline detection of ether gasoline additive and VOCs.Firstly, we presented a new sheet membrane inlet method for rapid determination of ethersgasoline additives (Methyl tert-butyl ether MTBE, ethyl tert-butyl ether ETBE, methyltert-amyl ether TAME and isopropyl ether DIPE) in water. Poly-dimethylsilane (PDMS) is themost widely used membrane material and it shows high sensitivity for VOCs.ME-SPI/PEI-TOFMS is a soft ionization for online analysis, and it enhances the abundances ofthe ions characteristic of the molecular masses by reducing the fragmentation of analytes andthus the complexity of the mass spectrum. This paper detailedly studied the membranethicknesses, temperature, areas, carrier gas and other paremeters which relevant to signalintensity and response time. Under the typical conditions, a single sample analysis time is lessthan100s，and the limits of detection for MTBE, ETBE, TAME and DIPE were5.5、4.8、3.3、4.3μg/L, respectively. The instrument has been successfully applied to rapid analysis of MTBEin simulated water with gasoline additives.Secondly，because of the long response times of VOCs on the common hollow-fibermembrane(HFM) inlet, we developed a in source stretched HFM inlet combined withME-SPI/PEI-TOFMS to trace analysis VOCs in water. Stretched HFM reduces the thicknessand increases surface area of membrane. Furthermore, we placed the stretched HFM under theVUV lamp with distance of15mm. This new design showed a significant decrease in response time and improvement in signal intensity. An excellent linear response (R2) higher than0.9972was observed for MTBE, ETBE, benzene, toluene, and p-xylene with the response times shorterthan150s, and the limits of detection for MTBE, ETBE, benzene, toluene, and p-xylene were1.3、1.2、0.25、0.32and0.26μg/L, respectively. In addition, we added another HFM into the ionsource and setup a membrane array, the initial results showed that the membrane array has apositive effect on improving the sensitivity of the instrument.