Centrifuged urine, internal standard (promazine), and ammonium formate buffer are mixed in an autosampler vial to achieve a 10-fold dilution of the specimen. Without additional pretreatment, 10 �L of the sample is injected onto a C18 reverse phase column for gradient analysis with ammonium formate/acetonitrile mobile phases. Drugs in the column eluent become charged in the ion source using positive electrospray atmospheric pressure ionization. Pseudomolecular drug ions are analyzed by a hybrid triple quadrupole linear ion trap mass spectrometer operated with a 264-drug selected ion monitoring (SRM) acquisition method that includes an information-dependant acquisition (IDA) algorithm.
