Comparison of SPE and fast LC to eliminate mass spectrometric matrix effects from microsomal incubation products

Twenty-seven highly diversified pharmaceutical compounds were used as a test set to evaluate matrix effects from microsomal media on LC/MS analyses. The individual effects of Tris buffer, NADPH and microsomes on ESI response were investigated. Direct flow injection MS/MS analysis, using no sample preparation or HPLC separation, gave an average of 2.2-5-fold matrix suppression in MS response from Tris buffer and NADPH. More polar analytes were affected the greatest. To reduce the loss in response, an automated solid phase extraction (SPE) procedure was developed. A much smaller average matrix effect was observed when samples were prepared using a Waters Oasis HLB 96-well SPE. As little as 1 ml of methanol (MeOH) was sufficient to elute most compounds with more than 80% recovery. Comparable results were obtained by directly injecting a protein-precipitated incubation onto a fast gradient LC separation prior to MS/MS detection. No advantage was seen by using both SPE and a fast LC separation prior to MS/MS analysis.