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Pulsed multiple reaction monitoring approach to enhancing sensitivity of a tandem quadrupole mass spectrometer.

ABSTRACT: Liquid chromatography (LC)-triple quadrupole mass spectrometers operating in a multiple reaction monitoring (MRM) mode are increasingly used for quantitative analysis of low-abundance analytes in highly complex biochemical matrixes. After development and selection of optimum MRM transitions, sensitivity and data quality limitations are largely related to mass spectral peak interferences from sample or matrix constituents and statistical limitations at low number of ions reaching the detector. Herein, we report on a new approach to enhancing MRM sensitivity by converting the continuous stream of ions from the ion source into a pulsed ion beam through the use of an ion funnel trap (IFT). Evaluation of the pulsed MRM approach was performed with a tryptic digest of Shewanella oneidensis strain MR-1 spiked with several model peptides. The sensitivity improvement observed with the IFT coupled in to the triple quadrupole instrument is based on several unique features. First, ion accumulation radio frequency (rf) ion trap facilitates improved droplet desolvation, which is manifested in the reduced background ion noise at the detector. Second, signal amplitude for a given transition is enhanced because of an order-of-magnitude increase in the ion charge density compared to a continuous mode of operation. Third, signal detection at the full duty cycle is obtained, as the trap use eliminates dead times between transitions, which are inevitable with continuous ion streams. In comparison with the conventional approach, the pulsed MRM signals showed 5-fold enhanced peak amplitude and 2-3-fold reduced chemical background, resulting in an improvement in the limit of detection (LOD) by a factor of ?4-8.

SUBMITTER: Belov ME

PROVIDER: S-EPMC3059105 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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Pulsed multiple reaction monitoring approach to enhancing sensitivity of a tandem quadrupole mass spectrometer.

Belov Mikhail E ME Prasad Satendra S Prior David C DC Danielson William F WF Weitz Karl K Ibrahim Yehia M YM Smith Richard D RD

Analytical chemistry 20110223 6

Liquid chromatography (LC)-triple quadrupole mass spectrometers operating in a multiple reaction monitoring (MRM) mode are increasingly used for quantitative analysis of low-abundance analytes in highly complex biochemical matrixes. After development and selection of optimum MRM transitions, sensitivity and data quality limitations are largely related to mass spectral peak interferences from sample or matrix constituents and statistical limitations at low number of ions reaching the detector. He ...[more]

PMID: 21344863

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Project description:There is an immediate need for improved methods to systematically and precisely quantify large sets of peptides in complex biological samples. To date protein quantification in biological samples has been routinely performed on triple quadrupole instruments operated in selected reaction monitoring mode (SRM), and two major challenges remain. Firstly, the number of peptides to be included in one survey experiment needs to be increased to routinely reach several hundreds, and secondly, the degree of selectivity should be improved so as to reliably discriminate the targeted analytes from background interferences. High resolution and accurate mass (HR/AM) analysis on the recently developed Q-Exactive mass spectrometer can potentially address these issues. This instrument presents a unique configuration: it is constituted of an orbitrap mass analyzer equipped with a quadrupole mass filter as the front-end for precursor ion mass selection. This configuration enables new quantitative methods based on HR/AM measurements, including targeted analysis in MS mode (single ion monitoring) and in MS/MS mode (parallel reaction monitoring). The ability of the quadrupole to select a restricted m/z range allows one to overcome the dynamic range limitations associated with trapping devices, and the MS/MS mode provides an additional stage of selectivity. When applied to targeted protein quantification in urine samples and benchmarked with the reference SRM technique, the quadrupole-orbitrap instrument exhibits similar or better performance in terms of selectivity, dynamic range, and sensitivity. This high performance is further enhanced by leveraging the multiplexing capability of the instrument to design novel acquisition methods and apply them to large targeted proteomic studies for the first time, as demonstrated on 770 tryptic yeast peptides analyzed in one 60-min experiment. The increased quality of quadrupole-orbitrap data has the potential to improve existing protein quantification methods in complex samples and address the pressing demand of systems biology or biomarker evaluation studies.

Project description:RATIONALE:Recent trends towards miniature and portable quadrupole mass spectrometry (QMS) entail challenges in instrumental sensitivity, which is influenced by 3D fringe field effects on ion transmission in the Quadrupole Mass Filter (QMF). The relationship of these effects with the gap from the ion source to the QMF entrance (source gap) is significant and little explored. We examine transmission characteristics experimentally and use the results to test the predictive accuracy of a recently developed 3D QMF simulation model. The model is then applied to directly investigate optimal transmission m/z ranges across multiple source gaps. METHODS:A portable single filter quadrupole mass spectrometer is used to analyse transmission characteristics across a range of common gases. We use an experimental approach originally proposed by Ehlert, enhanced with a novel method for absolute calibration of the transmission curve. Custom QMF simulation software employs the boundary element method (BEM) to compute accurate 3D electric fields. This is used to study the effects of the source gap on transmission efficiency. RESULTS:Experimental findings confirm a centrally peaked transmission curve; simulations correctly predict the optimal transmission location (in m/z) and percentage, and extend the experimental trend. We compare several methods for determining fringe field length, demonstrating how the size of the physical source gap influences both the length and the intensity of the fringe field at the QMF entrance. A complex relationship with ion transmission is revealed in which different source gaps promote optimal transmission at differing m/z ranges. CONCLUSIONS:The presented results map the relationship between the source gap and transmission efficiency for the given instrument, using a simulation method transferrable to other setups. This is of importance to miniature and portable quadrupole mass spectrometers design for specific applications, for the first time enabling the source gap to be tailored for optimal transmission in the desired mass range.

Dataset Information

Pulsed multiple reaction monitoring approach to enhancing sensitivity of a tandem quadrupole mass spectrometer.

Publications

Pulsed multiple reaction monitoring approach to enhancing sensitivity of a tandem quadrupole mass spectrometer.

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