Rapid mass spectrometry analysis of a rectilinear ion trap by continuous secular frequency scanning

Rationale Secular frequency scanning is a mass spectrometry (MS) analysis method in which the frequency of the auxiliary alternating current (AC) signal is scanned. It has low requirements for radio frequency (RF) power, which is beneficial for the miniaturization of the mass spectrometer. In this study, the MS performance in the reverse secular frequency scanning (RSFS) mode is optimized for a rectilinear ion trap (RIT), and a method for rapid MS analysis using continuous secular frequency scanning (CSFS) is proposed. Methods A RIT mass spectrometer with an auxiliary AC frequency scanning function was built. The resolution, tandem mass spectrometry and quantitation capability under the RSFS mode were characterized and optimized. Operation in the CSFS mode was then performed by scanning the frequency of the auxiliary AC signal continuously and periodically while maintaining the RF signal and the front Z electrode in the ion injection state, so that the ion injection and cooling were performed at the same time as the mass analysis. Results With this system, the RSFS mode achieved unit mass resolution at 332 Th, and the tandem MS analysis was completed without changing the RF amplitude at q = 0.4583 for reserpine. The limit of quantitation for imatinib was about 250 ng/mL with the determination coefficient R2 = 0.9981. In the CSFS mode, a single analysis cycle of less than 20 ms could be achieved, which is 14 times faster than the traditional sweep modes. In addition, 100% ion utilization can theoretically be achieved in the CSFS mode. Conclusions The CSFS mode is different from the traditional phased sequential operation mode of an ion trap mass spectrometer. By periodic scanning of the auxiliary AC frequency while maintaining ion injection, it is possible to improve the analysis efficiency of the mass spectrometer, which has the prospect of useful application in the field of rapid MS monitoring.