Design and simulation of a liquid-microjet time-of-flight mass spectrometer with a femtosecond laser ionization source

A liquid-microjet (LJ) linear time-of-flight (TOF) mass spectrometer, coupled with a femtosecond laser ionization source, has been designed for direct measurements of mass spectra of liquid aqueous solutions. Two main features of our designed spectrometer involve the coupling of a liquid microjet nozzle to a conventional ion optics and the application of femtosecond pulses for mass spectral ionization. The detailed design, construction, and simulation of this new spectrometer are presented. More importantly, we combined the experimental tests with the simulated electric fields and ion trajectories to investigate the performance of the designed spectrometer, especially the kind of disturbances of the nozzle electric field on the conventional ion optics. In our current design, the optimal E/R (E: extractor, R: repeller) electrode voltage ratio was found to be similar to 0.71 when the voltages on the R, E and G (ground) electrodes were set to be 1500, 1060 and 0 V, respectively, whilst the voltage on the N nozzle electrode was required to be around 1250 V. The capability of the designed spectrometer has been demonstrated by recording the simulated mass spectra of the water, benzene and cytidine with their mass/charge ratios of 18, 76 and 243, respectively. This work shall be helpful for the development of new all-liquid-phase mass spectral technology to be employed in the diagnosis of diseases by the mass analysis of human body fluids.