Sensitivity electrospray ionization mass spectroscopy

The majority of reports have used electrospray ionization mass spectroscopy (ESI-MS) as an analytical detection method because of its sensitivity and the soft namre of its ionization procedure, which generally only leads to the detection of the molecular ions of the positive library members. Many separation techniques have been coupled to ESI-MS, including affinity chromatography (49), size exclusion chromatography (50, 51), gel filtration (52), affinity capillary electrophoresis (53-58), capillary isoelectric focusing (59), immunoaffinity ultrafiltration (60), and immunoaffinity extraction (61). ESI-MS has also been used alone (62) to screen a small carbohydrate library. Other examples reported alternative analytical techniques such as MALDI MS, either alone (63, 64) or in conjunction with size exclusion methods (65), or HPLC coupled with immunoaffinity deletion (66). 

There are a variety of other spectroscopy techniques available for investigating reaction kinetics. However, MALDI-TOF-MS allows for the determination of rate constants regardless of the incorporation of a chromophore, and at a wide variety of buffer concentrations. Both of these advantages are useful if one wishes to study enzymatic reactions under naturally occurring conditions. The advantages of MALDI-TOF-MS can be compared to spectrophotometric methods, which require a chromophore, and electrospray ionization mass spectrometry, which is sensitive to buffer concentrations. As MALDI-TOF-MS is an off-line technique requiring quenching for the analysis we performed, a rapid mixer must be incorporated into the system. 

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