Events

Electrospray Ionization Mass Spectrometry in the Femto Regime: the Softness, Ionization Efficiency, and Individual Ions

Electrospray ionization (ESI) is an indispensable mass spectrometry method for solution phase analytes. However, ESI still has quite a few major limitations such as 1) non-uniform ionization efficiency that affects quantitative analysis; 2) harsh or extreme chemical environment caused by the evolution of the charged droplets; 3) higher (nanoamps) than needed (picoamps) ion currents leading to wasteful sample utilization leads and instrument contamination. The non-ideal ionization efficiency of ESI is not determined, and explained by existing chemical properties. In contrast, analyte charging in solution phase is predictable based on pH and pKa. New experimental and theoretical approaches are required to charging process in ESI, and to eventually overcome the limitations.

Reducing the flow rate of ESI to produce smaller and more efficiently charged droplets is a known strategy to improve ESI performance. In the past few decades, microflow, nanoflow, and picoflow ESI have been developed with increasing sensitivity and specific niche in various applications. To reach theoretical optimum conditions, the Li group is developing methods to conduct ESI with femtoamp (fA) currents, femto flow (fL/min), and from localized nanoscale meniscus. This seminar discusses the new properties of ESI in these femto regimes. Hydrophilic analytes including glycans, glycopeptide, and intact proteins were ionized at enhanced efficiencies that surpass prior literature reports. New equations are developed to calculate the size of nanoscale initial charged droplets. The femto ESI regime also enabled the analysis of environmental contaminants, directly from nonpolar extraction solvent. Lastly, we demonstrate how femtoESI could facilitate individual ion mass spectrometry, to enable the ultra-soft analysis of fullerene derivatives, and to allow atomic efficient deposition of noble metal nanostructure.

Hosted by  Professor Jason Zhang