Quantitation-Enhanced Data-Dependent MS/MS scanning on a triple stage quadrupole mass spectrometer enables simultaneous metabolite identification and quantitation of a parent drug. The selectivity provided by this technique helps to increase the detection of metabolites. When the QED-MS/MS and RER techniques are coupled, the structure and concentration profiles of parent drugs and metabolites can be obtained simultaneously, thus increasing the bioanalytical throughput in drug discovery laboratories.