| Mass spectrometry is a method in which substances are first ionized and then the detected ions are separated by their mass to charge ratio(m/z)in a vacuum environment by electric or magnetic field.Measuring ion mass accurately can determine the composition of compound.As a representative of modern analytical instruments,mass spectrometer has been widely used in many fields such as materials science,criminal investigation,life sciences,environmental monitoring,medical and health,food safety,manned spaceflight,and national security.In recent years,with the continuous development of mass spectrometry technology,it requires that the mass spectrometry detection equipment is more delicate,easier to carry and move.Therefore,more and more scientific research investments are focused on the instrument’s portability and miniaturization.However,the detection sensitivity of the miniaturized mass spectrometer is far from meeting the requirements.Most of the ion are lost in the ion transport device,and only a small number of ions can reach the mass analyser in the high vacuum area.Ion funnel is a new type of ion transfer device which could greatly improve ion transmission efficiency,due to its effectiveness of ion focusing in high pressure region.For the problem of large size and complex structure of classical ion funnel,this paper designed a miniaturized ion funnel.The total length of the newly designed miniaturization ion funnel was 2/3 of classical ion funnel,and it had a more simple circuit design and good transmission efficiency.In the research approach,this paper used a combination of theoretical simulation and experimental verification.The specific research contents and conclusions were as follows:Firstly,through theoretical analysis of the RF electric field inside the ion funnel,we found the suitable size range of the miniaturized ion funnel.Secondly,electric field simulation software SIMION were used to model the miniaturized ion funnel with different geometric parameters,ion trajectory simulation software AXSIM were used to simulate the ion trajectory inside the ion funnel,and calculated the transmission efficiency of ion.The simulation results showed that when the ion funnel electrode thickness was 1.0 mm,the electrode spacing d was 1.6mm and the number of electrodes was 34 pieces,the ion transport efficiency reached the maximum.The effect of electrical parameters on the performance of miniaturized ion funnel was further studied,and simulation results showed that when RF frequency was 0.7 1.2MHz,RF amplitude was 80 120 V,and DC voltage gradient was 9~15V/cm,a high transmission efficiency close to 95% was achieved for ions with mass to charge ratio(m/z)greater than 100 Da.Finally,based on the theoretical simulation,the miniaturized ion funnel was processed and manufactured,and an electrospray ionization source ion trap experiment platform was built to verify the transmission performance of the miniaturized ion funnel.The experimental results showed that used a miniaturized ion funnel instead of a skimmer,the ion abundance of the mass spectrum increased by six times at each scanning rate,which means the sensitivity of the entire instrument increased by six times.In the experiment process,the electrical parameters of the miniaturized ion funnel were changed to obtain the results consistent with the simulation,which further validated the reliability of the research method. |
