Research of Orthogonal-injection and Delayed-extraction MALDI

An orthogonal injection (OI) home-made reflectror type time-of-flight (TOF) mass spectrometer has been constructed with a matrix-assisted laser desorption/ionization (MALDI) source. Ions generated by MALDI are measured using a pulsed voltage delayed extraction method. The laser used is a frequency quadrupled Nd:YAG laser with output at wavelength of 266 nm, the matrix used here is 2,5-dihydroxybenzonic acid (DHB), and the analytes are Malachite green and peptides. Measurements of resolving power and statistical evaluation of the mass accuracy are reported here. The results indicate that resolving power in the range of 3400 to 4000 (full width at half maximum), the average error of the mass accuracy is below 0.0075%, A perfectly linear (m/z)1/2 versus t plot is found. Finally, the initial velocity distribution of analyte and matrix ions in the range of 400~1000 m/s is measured.