Reduction of signal suppression effects in ESI-MS using a nanosplitting device

Electrospray ionization mass spectrometry is a valuable tool in the identif ication and quantification of drug metabolites in biological fluids. Howeve r, there are many instances where matrix components present in these fluids interfere with analyte detection and prevent the acquisition of accurate o r complete results. In some instances, the matrix can suppress ionization t o such an extent that analytes are completely undetectable by MS. In this w ork, we investigate how ionization and ion-transfer efficiencies are affect ed by drastically reducing the flow into the MS. A postcolumn concentric fl ow-splitting device was constructed to allow the measurement of analyte sig nal and ionization suppression across a range of flow rates (0.1-200 muL/mi n). Using this device, the effects of flow rate on signal intensity and ion ization suppression were measured in analytical experiments that included f low injection analysis MS, postcolumn addition LC-MS, and on-line LC-MS ana lysis of metabolites generated from rat liver microsomes. The device used t o deliver 0.1 muL/min flows is referred to as a nanosplitter because it ach ieved high split ratios (2000: 1), producing flow rates comparable to those observed in nanoelectrospray. The nanosplitter maintained chromatographic integrity with high fidelity and allowed the direct comparison of analyte s ignal across a range of flow rates (0.1-200 muL/min). A significant improve ment in concentration and mass sensitivity as well as a reduction in signal suppression is observed when the performance at 200 versus 0.1 muL/min flo w rate is compared. Using this specially designed concentric splitting devi ce, the advantages of ultralow flow ESI were easily exploited for applicati ons employing large bore chromatography.