ディレイライン検出器を用いた投影型イメージング質量分析における有効な信号処理技術の開発

抄録

Simultaneously detecting arrival times and two-dimensional (2D) positions of individual ions is essential for imaging mass spectrometry (imaging MS) in the microscope (stigmatic) mode which is superior in terms of spatial resolution to the more commonly used microprobe mode imaging MS. A detection system for microscope mode imaging MS was developed using an in-house constructed laser desorption/ionization (LDI) linear time-of-flight mass spectrometer as a platform for use and a delay line detector (DLD) was used as the position-sensitive ion detector. A signal readout system for DLD was configured using high-speed analog-to-digital converter (ADC) modules to detect multiple m/z-resolved ions. An efficient acquisition/processing technique for the data, which was acquired using an ADC-based system was developed to achieve an increased permissible laser pulse repetition rate, reduced data size and real time data processing. Multiple stigmatic images of m/z-resolved ions were obtained from a model sample formed of micro-dots of three types of dyes without using an ion gate for m/z selection. The measurement time was 18 minutes at an ionizing laser pulse repetition rate of 10 Hz, and the size of the data, which was comprised of lists of flight times and 2D positions of individual detected ions in ASCII format, was below 5 MB. The ability of LDI microscope mode imaging MS to obtain a complete series of m/z-resolved snapshots of LDI-generated ions in a single measurement was demonstrated. The present approach provides a realistic solution that can make use of a high-speed ADC for the DLD signal readout, and may facilitate further technical developments of microscope mode imaging MS.