ABSTRACT
As mentioned in Section I, ESI-MS of oligonucleotides can be performed using different mass-spectrometry instrumentation, each with its own advantages and peculiarities. Most commonly used are quadrupole [1,13,23,24,32,34-37] and triple quadrupole mass spectrometers [14,15,33,38-50], the latter offering the possibility of performing sequencing of the oligonucleotides using CID fragmentation. Recently, a new hybrid mass spectrometer, coupling a quadrupole inlet to a time-of-flight mass spectrometer, allowing CID fragmentation but with a higher mass resolution and sensitivity (up to a factor of 100) compared to a conventional triple quadrupole was used to determine oligonucleotides [51]. Higher sensitivity compared to quadrupole mass analyzers can also be attained by using ion trap mass spectrometers to analyze oligonucleotides with ESI-MS [52-54]. An extremely high mass resolution (RP=105 ), especially useful in sequencing using molecular fragmentation techniques, combined with a high sensitivity can be obtained by using a FTICR mass spectrometer [12,18,31,55,56].
