Besides portability and increasingly improved performances, the ability of screening target analyte from complex compounds is a crucial function of miniature mass spectrometers, especially for in situ analysis. Selected reaction monitoring (SRM) and multiple reaction monitoring (MRM) operation modes are the most widely used mass spectrometry operation methods for target analyte quantitation. As a continuous effort to improve the analytical performances of the “brick” mass spectrometer, built in-house, pseudo-SRM and pseudo-MRM modes were realized on the linear ion trap mass analyzer in the device. A broadband excitation waveform in both time and frequency domains, namely, the Grid-SWIFT waveform, was constructed and compared with the conventional SWIFT waveform. By isolating target ions during the ion introduction period using the Grid-SWIFT waveform, target ions could be efficiently accumulated inside the ion trap without experiencing space charge effects and interferences from nontarget ions in the samples. As a result, not only the detection sensitivity of the target analyte could be increased, but also the quantitation accuracy over a relatively wide concentration range could be improved.

A better understanding of nanoelectrospray ionization (nano‐ESI) would be beneficial in further improving the performances of nano‐ESI. In this work, the pulsed high‐voltage (HV) nano‐ESI has been electrically modeled and then systematically characterized by both voltage‐current and mass spectrometry measurements. First, the equivalent resistance of a nano‐ESI source changes with respect to both emitter tip diameter and the HV applied. Increased voltage could improve both spray current and ionization efficiency of the pulsed HV nano‐ESI. Compared with conventional DC HV method, a pulsed HV has less heating effect on the capillary tip and thus allowing the application of a much higher voltage onto a nano‐ESI source. As a result, a pulsed HV nano‐ESI could further boost the ionization efficiency of nano‐ESI by employing even higher voltages than conventional DC nano‐ESI sources.

In this study, a new method/mechanism to manipulate ions in solution was developed, based on which liquid-phase ion trap was built. In this liquid-phase ion trap, ion manipulations conventionally performed in a quadrupole ion trap or in a trapped ion mobility spectrometer placed in a vacuum were achieved in solutions. Through theoretical derivation and numerical simulation, it is found that ions have different motional characteristics than those in vacuum. Instead of a radio frequency quadrupole electric field, tunable DC electric fields together with a constant liquid flow were applied to control ion motions in solution. Different ions could be trapped and focused in a potential well, and ion densities could be increased by over 100-fold. By adjusting the DC electric field of the potential well, trapped ions could be transferred into another trapping region or sequentially released for detection. Ions released from the liquid-phase ion trap were then detected by a mass spectrometer interfaced with an electrospray ionization source. Since the ion manipulation mechanism in solution is different and complementary to that in vacuum, the use of a liquid-phase ion trap could also boost detection sensitivity and the mixture analysis capability of a mass spectrometer.

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