Better Mass Spec Results Off-Line

Courtesy of Advion BioSciences Electrospray ionization (ESI) mass spectrometry (MS), in which peptides are ionized as they elute from a liquid chromatography (LC) column, typically requires high flow rates, which reduces sensitivity and consumes large quantities of sample. Nanoelectrospray techniques for proteomics are more efficient, but can be labor-intensive and time-consuming.

By | April 7, 2003

Courtesy of Advion BioSciences

Electrospray ionization (ESI) mass spectrometry (MS), in which peptides are ionized as they elute from a liquid chromatography (LC) column, typically requires high flow rates, which reduces sensitivity and consumes large quantities of sample. Nanoelectrospray techniques for proteomics are more efficient, but can be labor-intensive and time-consuming.

To make the process more practical for high-throughput experiments, Ithaca, NY-based Advion BioSciences recently introduced the NanoMate™ 100, an automated nanoelectrospray system that interfaces directly with most commercially available ESI-based mass spectrometers. The system uses ESI Chips™, arrays of 100 nozzles that ionize samples individually and infuse them directly into the mass spectrometer. These arrays are disposable and each sample travels through a separate nozzle, completely eliminating cross-contamination. Samples are aspirated from 96-well plates via pipette tips that seal against the nozzle inlets on the back of the chip; any unused sample can be returned to the plate.

Tom Kurz, chief operating officer, explains that one of the most common protein-identification techniques is tryptic digestion followed by online LC/MS of the resulting peptides. As the sample elutes off a fractionation column directly into the mass spectrometer, the user has relatively little time to analyze the information contained in each chromatographic peak. Because the NanoMate system can accommodate small sample volumes, it can analyze individual fractions that have been separated offline by HPLC into individual wells of a microtiter plate. These fractions can then be examined by MS over a longer period of time to increase peptide sequence coverage, Kurz says.

The NanoMate also can be used for small-molecule quantitation. The common method for such analysis is online LC/MS, which concentrates the sample and thus enhances sensitivity, yet is plagued by relatively long run times, extensive method development, and the potential for cross-contamination. Kurz notes that the conventional alternative is flow-injection analysis, in which the sample is introduced into the system via a solvent flow stream, diluting the sample and reducing sensitivity. The NanoMate system bypasses the solvent flow stream, retaining the sensitivity of LC/MS without the need for online chromatography, says Kurz. Eliminating this step shortens the run time to less than one minute, he adds, and shortens method development time, too.

In March Advion and Thermo Electron of Waltham, Mass., announced an agreement to sell, market, and support an automated nanoelectrospray MS system composed of Advion's NanoMate 100 and ESI Chips and Thermo Finnigan's LCQ™ Deca XP Plus ion-trap mass spectrometer.

--Aileen Constans

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