Direct Analysis Using Miniature Mass Spectrometers: A Fast On-Site Analytical Tool for Toxicology

Direct Performance of Triple-Stage Tandem Mass Spectrometry Analysis Using Dual-Direction Dipolar Excitation in a Digital Linear Ion Trap

The ion trap mass spectrometer offers a unique advantage over other mass spectrometers by enabling multistage tandem mass spectrometry analysis with a single mass analyzer. It is employed to generate fragment ions through collision-induced dissociation (CID) usually by applying alternating current (AC) signals to a pair of electrodes for dipole excitation. The process of achieving double-stage tandem mass spectrometry analysis (MS/MS) in the mass spectrometer involves successive stages of injection, cooling, isolation, excitation, and scanning. For triple-stage tandem mass spectrometry analysis (MS/MS/MS), additional stages of isolation, cooling, and excitation need to be added based on the MS/MS analysis, resulting in a complex and time-consuming mass spectrometry workflow. In this study, a digital ion trap technology with the method of simultaneously applying dipole excitation signals to two pairs of electrodes in the ion trap was developed. This allows fragmentation of the precursor ion in one direction while exciting the first-generation product ions in the other direction, enabling direct acquisition of MS/MS/MS spectra. This approach simplifies the process of tandem mass spectrometry, as demonstrated by experimental studies on methamphetamine, which show that dual-direction excitation effectively reduces workflow and enhances the intensity of product ions. Additionally, the method of direct MS/MS/MS spectra achieved through dual-direction excitation in a digital ion trap mass spectrometer allows for a lower q value of the precursor ion owing to a pseudopotential well depth that is 1.648 times greater than that of a traditional sinusoidal ion trap. The experiments of analyzing high concentration n-butyl acetate and isobutyl acetate have shown that the implementation of MS/MS/MS analysis using dual-direction excitation can provide more mass spectral information and effectively distinguish between the two isomeric samples. The results of direct triple-stage spectra obtained by this technique for several typical volatile hazardous chemicals demonstrate the method's capability for rapid analysis and detection of such substances. In summary, the developed method of dual-directional excitation coupled with digital ion trap technology enables direct performance of triple-stage tandem mass spectrometry analysis, improving fragment ion intensities and providing more valuable mass spectral information. It offers advantages such as simplified workflows, faster analysis, and enhanced accuracy for analyzing compounds with low mass fragment ions.

Quantification and evaluation of ion transmission efficiency in two-stage vacuum chamber miniature mass spectrometer

Miniature mass spectrometer is more compact and portable than traditional commercial mass spectrometry, with more potential for application outside the laboratory. However, a miniature mass spectrometer is less sensitive than a commercial instrument, limiting its application scenarios. The ion transmission efficiency of the instrument is an essential factor affecting the sensitivity. Still, there are few works of literature on the quantitative study of the ion transmission efficiency of each component from a systematic perspective. In this paper, the Faraday cup coupled with a microcurrent signal testing instrument was used to measure the ions generated by nanoelectrospray ionization (nano-ESI), which have successfully gone through several components. Then the ion transmission efficiency of each component was quantified. Results showed that the front lens had the highest ion transmission efficiency of 39.7%, whereas the inlet and skimmer had the lowest ion transfer efficiency of 0.8% and 17.1%. Next, the influence of control parameters on ion transmission efficiency of critical components was investigated. If optimized, the ion funnel and the skimmer had the potential to improve their transmission efficiency by 120% and 79%, respectively. This paper shows the decreasing intensity distribution of ions in the whole transmission process and the transmission efficiency of each component, which can guide for improving the sensitivity of the miniature mass spectrometer.