Method and system for high-throughput quantitation of small molecules using laser desorption and multiple-reaction-monitoring

Abstract

A mass spectrometry quantitation technique enables high-throughput quantitation of small molecules using a laser-desorption (e.g., MALDI) ion source coupled to a triplequadrupole mass analyzer. The ions generated from the ion source are collisionally damped / cooled, and then quantitatively analyzed using the triple-quadrupole analyzer operated in the multiple-reaction-monitoring (MRM) mode. Significantly improved measurement sensitivity is obtained by applying laser pulses to the ion source at a high pulse rate of about SOOHz or higher. This allows the data acquisition to be performed rapidly, and the speed of about one second for each sample point on the ion source target has been achieved.

Description

RELATED APPLICATION [0001] This application claims the priority of U.S. Provisional Application 60 / 368,195, filed Mar. 28, 2002.FIELD OF THE INVENTION [0002] The present invention relates generally to mass spectrometry, and more particularly to a way to perform high-throughput quantitation of small molecules. BACKGROUND OF THE INVENTION [0003] Quantitative analyses of pharmaceutically and biologically important compounds, such as drugs and metabolites, are important applications of mass spectroscopy. Traditionally, ion sources based on electrospray (ESI) ionization and atmospheric pressure chemical ionization (APCI) are used in combination with triple-quadrupole mass spectrometers to provide quantitative analysis. The combination provides both high sensitivity and high specificity. ESI and APCI both generate ions from flowing liquid streams, and are therefore used by pumping organic and aqueous solvent streams containing the compounds to be analyzed through the source. Liquid chroma...

AI Technical Summary

Benefits of technology

[0009] In accordance with the invention, the ions generated by laser-desorption of a sample material of a small molecule are collisionally damped / cooled, and then quantitatively analyzed using the triple-quad operating in the multiple-reaction-monitoring (MRM) mode. In according with a feature of the invention, significantly improved measurement sensitivity is obtained by applying laser pulses to the ion source at a high pulse rate, preferably about 500 Hz or higher. This allows the data acquisition to be performed rapidly, and the speed of one second or so for each sample point on the ion source target has been achieved.

Problems solved by technology

During the scan, samples are injected sequentially, at a rate in the order of 1 per 10 second, due to limitations in autosamplers, as well as limitation imposed by the natural width of the eluting peak Once the sample has passed through the ion source, it is ionized and dissipated in the source, with only a small fraction of the ions generated from the sample actually being sampled into the mass spectrometer system.

However, until recently, there has been no viable method of doing true MS / MS with this type of instrument.

This technique provides relatively poor sensitivity and mass accuracy, and is not considered to be a high performance MS / MS technique.

The MALDI technique also suffers from the fact that while the mass accuracy and resolution can be very high (up to 30,000 resolution at low mass, and accuracy of a few parts-per-million), these important features are difficult to achieve because they depend on the microstructure of the sample surface (roughness), the laser fluence, and other instrumental characteristics which can be hard to control.

Some previous attempts have been made to use MALDI for quantitative analysis, but they have met with limited success because of the poor precision obtained with MALDI / TOF.

However, there is no recognition that this might offer improved ability to measure sample concentrations quantitatively.

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