Improving the performance of MALDI-TOF in oligonucleotide analysis using a new SDIFA technology.

A new technology termed SDIFA is developed to improve the mass resolution of linear matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in oligonucleotide analysis. Unlike the currently used delayed extraction method, SDIFA allows electrical isolation of the sample holder from ion extraction/acceleration and selectively samples part of the desorbed ions, thereby reducing the initial velocity distribution and improving resolution. In addition, a method was introduced to improve the space focusing of TOF. Isotope-limited mass resolution was obtained for oligonucleotides of up to 62 mer, and the true instrumental resolution reaches to 1,800 at 19.2 kDa. It was also demonstrated that excellent resolution was obtained across a large mass range using a single setting of acquisition parameters. This feature allows unambiguous identification of multiple A/T heterozygote samples in a mass range of 5,200-7,800 Da. Moreover, compared with DE, the performance of SDIFA was more stable, reproducible, and less dependent on the experimental conditions including the laser power, sample spots, sample substrates, delayed time, and extraction field strength. This enhanced ease of data acquisition is the key to automated spectrum acquisition.