DETECTION OF OLIGONUCLEOTIDES BY EXTERNAL INJECTION INTO AN ION-TRAP STORAGE REFLECTRON TIME-OF-FLIGHT DEVICE/

The detection of oligonucleotides has been studied using external inje ction of Matrix-assisted laser desorption/ionization (MALDI) produced ions into a quadrupole ion trap storage device. The ions stored in the trap are then detected by pulsed DC ejection into a reflection time-o f-flight mass spectrometer. It is shown that by using a low accelerati on voltage from the probe tip and external injection into the trap tha t 3-mers to 9-mers can be stored far 20-50 ms and detected as intact i ons. In comparison, direct MALDI inside the trap resulted in extensive fragmentation as a function of storage time, Using the external injec tion method with a He buffer gas in the frap yields a resolution of 25 0-400 in the ion trap storage/reflectron time-of-flight mass spectrome ter. The resolution can be further enhanced to 400-800 using a bipolar extraction method, In addition, the trapping efficiency for the injec tion of externally produced ions into the trap can be enhanced using a dynamic trapping method. The MALDI mass spectra produced by this meth odology result in excellent signal-to-noise ratio due to the capabilit ies of the trap for eliminating low mass matrix background from the sp ectra, (C) 1997 by John Wiley & Sons, Ltd.