Improve And Characterize A Desktop Time-of-flight Mass Spectrometer With Atmospheric Pressure Interface

Ambient mass spectrometry realizing ionization under ambient conditions withoutcomplicated sample pretreatment has become a hotpot issue in mass spectrometry and madegreat progress in pharmaceutical testing, environmental pollution detection, food safety testingand so on. It’s pity that all related research in China is based on the imported instruments becauseour mass spectrometer lags behind other nations. With the starting point of improvement andapplication of TOFMS with atmospheric pressure interface, a homemade time-of-flight massspectrometer (TOFMS) was designed and constructed.The homemade TOFMS comprises vacuum system, mechanical structure, signal detectionsystem, power supply control system and so on. Some related improvement work is detailed asfollowing: A kind of electrospray ionization is designed and constructed for instrument adjusting;Atmospheric pressure interface involving function of collisional induced ionization for structuralanalysis can also be developed; Duplex radio-frequency voltages of different resonant frequencyare supplied for radio-frequency quadrupole(RFQ) for mass transfer improvement; Becausecollision between ion and neutral gas will do some effect on ion transportation and focusingeffect, direct current quadrupole(DCQ) with grid is invented; Power supply polarity switchingmethod and improved detection system structure are also designed for bipolar ion detection.Instrumental performance characteristics and samples testing are obtained with theelectrospray ionization, in addition, the results of experiment are also discussed. It’s proved thatAs an atmospheric pressure ionization interface, the molecule ion reactor leads to iondecomposition. The mass fragmentograms were constructed from a series of mass spectraobtained by adjusting the voltage difference between two electrodes in molecular ion reactor.When using duplex radio-frequency voltage with resonant frequency0.7MHz and1.4MHz, masstransfer range was from m/z33to m/z4549with high concentration of CsI sample(1×10-3mol/L). Both positive and negative polypropylene glycol1000species were observed inspectrum for the power supply polarity switching successfully. It’s demonstrated that mass resolving power was over exception, for the mass analyzer provided mass resolving power2500,4900,6000and7500at m/z38.96,132.91,609.28and1009.58, respectively. By plotting peakarea of target ion to the sample concentration, two calibration curves with linearity over0.99,reserpine and1-hexane sodium sulfonate, were established respectively. A detection limit (S/N=3)of the method for reserpine was1pg/μL, while the dynamic range was lower than103. What’smore, various samples such as polymer, peptides, pharmaceutical, amino acid and hydroxylatedmetabolites of polycyclic aromatic hydrocarbons (OH-PAHS), were inspected. All resultsindicated that this homemade TOFMS met requirements of ambient mass spectrometry.To further improve Instrumental performance characteristics, the next step in this work willbe focused on sensitivity, dynamic range and anti-pollution. Besides providing experiences andvaluable references for designing mass spectrometer, it’s hoped that all the efforts made are forthe purpose of supporting pharmaceutical testing, environmental pollution detection, food safetytesting.