SelexION® Technology: The Solution to Selectivity Challenges in Quantitative Analysis

Significance of the Topic

High selectivity is essential for accurate quantitative mass spectrometry assays, but complex sample matrices often introduce co-eluting interferences or elevated baselines that compromise limits of quantitation, dynamic range and data processing efficiency. Traditional solutions—longer chromatography, extensive sample cleanup or manual peak integration—are time-consuming and reduce throughput. Integrating an additional separation dimension at the ion level can overcome these challenges, enabling more robust, high-speed quantitative analyses.

Objectives and Study Overview

This study presents SelexION® Technology, a differential mobility separation (DMS) interface combined with chemical modifiers, applied on QTRAP® and TripleTOF® systems. It aims to demonstrate how planar DMS geometry and volatile reagents enhance analyte selectivity, reduce matrix effects, separate isomers and maintain rigorous bioanalytical performance under regulated conditions.

Methodology and Instrumentation

SelexION® employs a compact DMS cell with two parallel plates (10×30 mm, 1 mm gap) positioned between the curtain plate and orifice. An asymmetric RF waveform (separation voltage, SV) alternates high and low fields, causing ions to drift differently based on mobility. A compensation voltage (CoV) aligns target-ion trajectories while deflecting interferences to the cell walls. Volatile chemical modifiers (e.g., isopropanol, methanol, acetone) are introduced into the curtain gas to create reversible ion clusters, adding a chemical dimension to mobility differences.

Main Results and Discussion

• Clenbuterol in urine: With isopropanol modifier, all three MRM transitions showed complete removal of matrix interferences. Calibration (63 pg/mL–125 ng/mL) and three QC levels over four days met bioanalytical criteria (inter- and intra-day CV <15 %). CoV stability remained within 0.01 V over 24 h.

• Pentoxifylline in plasma: A high baseline in the 279.2→99.2 transition was reduced by 20× signal-to-noise when using methanol as modifier, enabling a lower LOQ and extended linearity.

• Ephedrine vs. pseudoephedrine: These isobaric diastereomers, indistinguishable by chromatography and identical in MRM, were fully resolved in CoV space by applying acetone modifier (CoV offset –45 to –32 V), demonstrating essential isomer separation for accurate quantitation.

Benefits and Practical Applications

• Enhanced selectivity reduces reliance on extended chromatography and complex sample prep.
• Rapid switching between DMS and conventional modes allows flexible workflows.
• Improved LOQ and dynamic range via interference removal and baseline suppression.
• Robust CoV stability ensures reproducible quantitation for regulated bioanalysis.
• Compact, tool-free installation supports routine use in high-throughput laboratories.

Future Trends and Possible Applications

Expanding the range of chemical modifiers could further tune separation for diverse analyte classes. Integration with ultra-high-pressure LC and high-resolution MS may advance lipidomics, metabolomics and proteomics. Automated CoV optimization and real-time modifier control could improve method development speed. Applications in clinical diagnostics, environmental monitoring and food safety are promising areas for adoption.

Conclusion

SelexION® Technology introduces a higher dimension of selectivity by combining planar differential mobility separation with chemical modifiers. It effectively eliminates matrix interferences, resolves isomers and maintains bioanalytical robustness and throughput. This innovative approach provides a powerful tool for quantitative mass spectrometry, addressing common selectivity challenges across complex matrices.

Reference

1. Schneider BB et al., Anal. Chem. 82, 1867–1880 (2010) Chemical effects in DMS–MS separation process.
2. Schneider BB et al., Int. J. Mass Spectrom. 298, 45–54 (2010) Planar differential mobility spectrometer as a pre-filter.
3. Schneider BB et al., Eur. J. Mass Spectrom. 16, 57–71 (2010) Control of chemical effects in DMS.
4. Krylov EV et al., Rev. Sci. Instrum. 81, 024101 (2010) Selection and generation of DMS waveforms.
5. SCIEX Technical Note RUO-MKT-02-2739-A. MRM3 quantitation for highest selectivity.