Scheme 2.
Schematic illustration of nucleoside detection via LC-QqQ-MS using m6Am as example. After chromatographic separation via RP-HPLC, nucleosides are ionized via electrospray ionization (ESI) by applying a defined fragmentor voltage in the QqQ-MS. The first quadrupole (Q1) acts as a mass filter and is set to permit only defined precursor ions into the collision chamber (q2). Here, precursor ions are fragmented via collision-induced dissociation (CID) with N2 into specific product ions. Degree of fragmentation depends on the collision energy applied. By cycling between different CEs, two (or more) specific product ions are produced from a single precursor ion. Q3 acts again as mass filter, permitting only defined product ions to the detector. The product ion giving the greatest response is used for quantification (quantifier) while other specific product ions are used as qualifiers. The respective quantifier/qualifier ratio allows for assessment of selectivity towards the analyte.