Development Of Rectilinear Ion Trap Mass Spectrometer And Ion Mobility Spectrometer

Part 1:Development of Rectilinear Ion Trap Mass SpectrometerMass spectrometry is perhaps the most widely used analytical technique,due principally to its high specificity in analyte identification as well as its high sensitivity and applicability to the analysis of a broad range of isotopes, elements,and chemical and biological compounds.Rectilinear ion trap(RIT)is a novel mass analyzer for mass spectrometer (MS).And RIT shows some unique advantages:it can be operated at pressures above 10^-3Torr,and has tandem mass spectrometry(MSⁿ)capability,and is easy to be designed and fabricated,and has a high efficiency for trapping ion with less space charge effect.The x,y electrodes were machined from 304-stainless steel and assembled with PEEK holders.Both x and y electrode are 40 mm in length.The half-distance between the x pair of electrodes(x₀)is 5.0 mm,and the half-distance between the y pair(y₀)was varied in different embodiments from 5.0 to 4.0 mm by adding shims between the y electrodes and the holder.The gap between the x and y electrodes is 1.0mm.Centrally located on the x electrodes are slits of 16.0 mm long and 1.0 mm wide.Two stainless steel plates without apertures are used as z electrodes located at a distance of 1.6 mm from the ends of the x,y electrodes and with an interelectrode distance(z₀) of 43.2mm.Based on RIT mass analyzer two kinds of mass spectrometer were built:an electron impact source(EI)mass spectrometer and an electrospray ionization (ESI)mass spectrometer.EI source is consisted of a filament,a box of ionization,an einzel lens,and an exclude electrode.And the electrons are emitted from Rhenium-Tungsten filament.ESI source is consisted of a spray needle,a capillary,a skimmer,a hexapole,an einzel lens and some auxiliary components.The gradient vacuum for ESI is well suited to the introduction of ions from atmospheric pressure to vacuum system.And only one rotary vane pump and one split turbo pump are used for three or four stages gradient vacuum,and the vacuum gets 10^-6mbar.This is a great design.An NI card and LabVIEW software are employed as data acquisition and control components.The parameters of RIT-MS are optimized,and some samples such as,PFTBA, tetrachloroethylene and carbon tetrachloride have been tested,and get some good results.A dual-source RIT-MS is developed for the first time,and an RIT-MS with two EI source has be built.This device can be used to do fundamental research of ion-molecule reactions.Part2:Development of Ion Mobility SpectrometerIon mobility spectrometry(IMS)is a simple,inexpensive and sensitive analytical method for the detection of organic trace compounds.In this paper an IMS with corona discharge source was constructed.In order to eliminate nitrogen oxides the corona discharge source was shielded with N₂.The corona needle was a thin platinum wire(0.2 mm diameter),and the target electrode was made of a 1-mm thick copper disc with a hole(2.5mm diameter)at the center,mounted and sealed inside the tube in front of the needle to create a point-to-plane geometry.In IMS cell,seven 1-mm thick copper guard rings were mounted.The guard rings were located 5mm apart from each other and connected by a series of 2MΩresistors to form the electric field.In the front of drift field a thin grid electrode was mounted as the gate.And a Faraday detector was mounted in the end of drift field. The IMS cell was an aluminum-alloy tube,and the components of ion source, electrode,gate and detector were mounted in it.Additionally,the cell included a gas flow system,a heating component,and a sample valve and so on.The gas system consisted of a Teflon pipe,a diaphragm pump and a flow rate control device.A lab-made power supply,a high-voltage component and a pulse electrocircuit were used on IMS.The ion current was amplified by current amplifier Keithley428 with a gain of 10⁸ or 10⁹ V/A(as required).An NI card and LabVIEW software were employed as data acquisition.The parameters of lab-made IMS,such as drift voltage,discharge voltage,gate time,flow rate of drift gas and shielding gas etc,were optimized.And some samples containing components,such as TNT,ether and xylene,have been tested,and some corresponding spectra were obtained.In this paper the development of RIT-MS and continuous corona-IMS were reported for the first time in China.