Desorption Electrospray Ionization

Ambient mass spectrometry—mass spectrometric analysis with no or minimal effort for sample preparation—has experienced a very rapid development during the last 5 years, with many different methods now available for ionization. Here, we review its range of applications, the hurdles encountered for its quantitative use, and the proposed mechanisms for ion formation. Clearly, more effort needs to be put into investigation of matrix effects, into defining representative sampling of heterogeneous materials, and into understanding and controlling the underlying ionization mechanisms. Finally, we propose a concept to reduce the number of different acronyms describing very similar embodiments of ambient mass spectrometry.

A recently developed prototype mobile laboratory mass spectrometer, incorporating an atmospheric pressure ionization (API) interface, is described. This system takes advantage of the small size, lower voltage requirements, and tandem MS abilities of the cylindrical ion trap mass analyzer. The prototype API MS uses small, low-power pumps to fit into a 0.1-m3 self-contained package weighing <45 kg. This instrument has been adapted to allow rapid interfacing to electrospray ionization, desorption electrospray ionization, and direct analysis in real-time sources. Initial data indicate that these techniques provide rapid detection and identification of compounds for quality control, homeland security, and forensic applications. In addition, this instrument is self-contained and compact, making it ideally extensible to mobile laboratory and field analyses. Initial MS and MS/MS data for analyses of drugs, food, and explosives are presented herein.

The application of continuous flow-extractive desorption electrospray ionization (CF-EDESI), an ambient ionization source demonstrated previously for use with intact protein analysis, is expanded here for the coupling of reversed phase protein separations to mass spectrometry. This configuration allows the introduction of charging additives to enhance detection without affecting the chromatographic separation mechanism. Two demonstrations of the advantages of CF-EDESI are presented in this work. First, a proof-of- principle is presented to demonstrate the applicability of hyphenation of liquid chromatography (LC) to CF- EDESI. LC-CF-EDESI-MS has good sensitivity compared to LC-electrospray ionization (ESI)-mass spectrometry. Second, the supercharging mechanism investigated in CF-EDESI provides an insight into a highly debated supercharging process in ESI. The results indicate that the mechanism of protein charging seen in HPLC-CF-EDESI is different from supercharging phenomena in co...