Samples are prepared by solid phase extraction prior to chromatography. Internal standards are added to 0.5 mL of sample mixed with HCL solution prior to applicationonto a preconditioned Waters Oasis� HLB cartridge. The cartridge is rinsed with 5% methanol in HPLC grade water. The samples are then eluted with methanol and evaporated to dryness. The samples are reconstituted with a 70:30 mix of mobile phases A and B, respectively. Ten percent of the samples are injected in the LCMSMS system.
Samples are analyzed on a Agilent HPLC system coupled to a Sciex API3000 triple quadupole mass analyzer used in the negative MRM mode. A gradient chromatography method separates the compounds from other components on a Waters Symmetry� C18 column. Each sample analysis requires 8 minutes.