APPLICATION OF MICRO-ELECTROSPRAY LIQUID-CHROMATOGRAPHY TECHNIQUES TOFT-ICR MS TO ENABLE HIGH-SENSITIVITY BIOLOGICAL ANALYSIS

A microbore electrospray (ESI) injection system has been adapted to ou r 9.4-tesla ESI FT-ICR mass spectrometer, greatly enhancing the stabil ity and sensitivity of the system. Spray was generated from micro-ESI needles made from sharply tapered, polished fused silica capillaries o f 25 to 50 mu m inner diameter. Micro-ESI permits low-level sample ana lysis by constant infusion at sub-mu L/min flow rate over a wide range of solvent conditions in both positive-and negative-ion mode. The sys tem is flexible and allows rapid conversion to allow routine LC/MS ana lysis on low-level mixtures presented in biological media. LC/MS analy ses were accomplished by replacing micro-ESI needles with capillaries packed with reverse phase retention media to permit analyte concentrat ion and purification prior to analysis (micro-ESI/LC). A unique nano-f low LC pumping system was developed, capable of producing a true unspl it solvent gradient at flow rates below 1 mu L/min. The micro-ESI/LC F T-ICR system produces mass spectra from a mixture of three neuroactive peptides at a concentration of 500 amol/mu L (5 fmol each total loade d) in biological salts with baseline separation, signal-to-noise ratio of >10:1 and mass resolving power >5000. These results represent a re duction in detection limit by a factor of similar to 2 x 10(6) over th e best previously published LC/FT-ICR MS data. (C) 1998 American Socie ty for Mass Spectrometry.