Development and Characterization of A Linear Matrix-assisted Laser Desorption Ionization Mass Spectrometer

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an important analytical technique for biological macromolecules, such as proteins, peptides and nucleic acid, especially in the field of microbial identification. On the basis of previous study, a linear MALDI-TOF MS was been designed and assembled for biological applications. The instrument comprised a vacuum system, a vacuum fast sample introduction system, an optical system, a time-of-flight mass analyzer, an ion source, a data acquisition system and an electronic control system. The ion source adopted two-stage source acceleration, delayed extraction and dynamic pulse focusing technique. The time-of-flight distance of field-free drift region was about 1 m. The optical system adopted a solid-state laser with adjustable frequency of 1-2000 Hz and spots of 20-100 mu m. The angle of incidence laser was controlled at 5 degrees. A series of experiments were carried out to further evaluate the instrument performances. It could not only analyze the samples more than 199 kDa, but also achieve isotope resolution at 1000-3000 Da and up to 900 (FWHM) at 5000-17000 Da. The minimum detectable concentration of gramicidin was 10 amol mu L-1, absolute sensitivity reached up to 2.56 amol. Independent detection of saliva samples from different targets showed that the instrument had higher producibility. We identified Escherichia coli and Shigella spp., which are two common bacteria but difficult to be differentiated by mass spectrometry, showing its potential identification for clinical microorganism. In summary, this instrument can play a role on clinical examination in the near future.