Development And Application Of Ion Transport System In Microwave Plasma Torch Mass Spectrometer

As a new ionization technology, Microwave Plasma Torch Mass Spectrometer(MPT-MS)has attracted widespread people’s attention, with low power, low consumption of gas and many other advantages. The standing wave created by ion source at the outlet of the torch pipe excites the support gas into plasma,and ionization of the sample is in the way of charge transfer.The identification of elements in the sample is achieved by detection analysis of the ion mass using the spectrometer ion masses.MPT has good capability of ionization for metallic elements, so the MPT- MS can undertake the task of testing the metal elements in water quality atthe scene. In order to better accomplish this task, the paper has carried out the research of the related technology and methods of ion transport systems, integrated the instrument with the MPT and quadrupole mass spectrometer(Mass Spectrometer, MS),and carried out the applied research of the MPT-MS for the detection of the metal element. Specific studies include:(1)Development of ion transport systemIon transport system is a key component of the mass spectrometer, which is responsible for the important task that ions generated under the atmospheric pressure environment efficiently transfer to the mass analyzer. The main function of the ion transfer system contains filtering out interfering substances, bounding ion radial divergence, controlling the ion flight kinetic energy,ect. Ion transmission system includes a variety of transmission parts,for example the deflection electrode, ion funnel, octopole transmission system, ion electrostatic lens, these ion transport components take different roles inside the mass spectrometer in different environments, cooperate with each other to complete the ion transport work The paper chooses suitable ion transmission components according to the actual needs of MPT-MS in different vacuum chamber, designs each ion transmission components by theoretical studies and simulation, optimizes the voltage parameters of the transmission member, and gives the appropriate member ion transport policy.(2)Development of phase modulation ion funnelIon funnel is an important component in ion transport system, it could effectively focuses the ion beam under high pressure conditions, however, the conventional ion funnel exists mass discrimination effect of low-mass ions. Two adjacent electrode sheets load the same amplitude, 180 °out of phase RF voltage in traditional ion funnel. This RF voltage driving method enables the ion funnel electrode sheets generating a steeper equivalent field,so that transmitting ions are trapped in the internal electric field. However, with shrinking of ion funnel aperture, the equivalent field for low mass ions completely closes to form a equivalent barrier in the ion funnel outlet. The equivalent barrier causes these ions can not fly out of the funnel which forms mass discrimination. This paper raises and develops a square wave phase modulation funnel towards the mass discrimination effect of low-mass ions, the funnel drives the ion funnel by the square wave with a phase difference,its internal equivalent potential has better focusing effect, it also greatly weakens the equivalent barrier at the export, and it can restrain the formation of mass discrimination effect. The quality of ions can be analyzed by simulating of ion flight path within the square-wave phase funnel. The drive circuit of square wave phase ion funnel drive circuit is designed by selecting the appropriate parameters such as radio frequency, phase, duty cycle.The experimental data shows that the new ion funnel under the same conditions improves signal strength compared to conventional ion funnel over the full mass range more than 50%,and increases 150% to 200% of the signal strength for the propylamine(m / z = 59), butylamine(m / z = 73) and melamine(m / z = 127) and other low-mass ions.(3)the integration and testing of the MPT-MS machineMPT-MS machine integration includes ion sources, vacuum system, ion transport system, ion detection system, measurement and control systems, ect. The new MPT-MS designed as a in-car instrumentation tests the on-site water quality by taking the best advantage of MPT. Thus,the mechanical structure of MPT-MS instrument integration is supposed to be compact and firm,during the installing, to ensure the instrument has the property of long-term stability.(4)the detection of trace metals in Water samples by MPT-MSAs a in-car instrumentation, MPT-MS needs a secure and stable atomized desolvation injection system. The atomized desolvation equipment based on Nafion tube are required to meet the demand. This equipment inhibits the loss during sample transfer process inside the tube.The collision-induced dissociation effect in the ion funnel has made up for the defect of MPT low power ion source, and the polyatomic ions generated by MPT ion source can be dissociated into single atom ions which can detected by mass spectrometer. By adjusting the amplitude of ion funnel RF voltage, different metal elements can be detected in a best way,so that MPT-MS can detect various metal elements effectively. Using practical sample, which is a mixed solution to simulate the actual sample after acid hydrolysis containing Cu, Ga, Sr, As, Rh, Y, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Au, Tl, Pb, Bi and other elements,tests the ability of MPT-MS multiple elements Simultaneous detection. The experimental result shows that detection limit of various elements of the MPT-MS has reached 0.02-1.4ng ? m L-1 magnitude.