Robust and Reproducible Protein Quantification in Plasma using the Evosep One and the Agilent 6495 Triple Quadrupole LC/MS

Importance of the Topic

Targeted protein quantification in complex biological fluids such as human plasma is critical for biomarker verification in research and clinical settings. High sensitivity, reproducibility, and throughput are essential to reliably measure low-abundance proteins and support large-scale studies.

Objectives and Study Overview

This study evaluates the performance of a novel LC/MS platform combining the Evosep One chromatography system with the Agilent 6495 triple quadrupole mass spectrometer. The aim is to demonstrate robustness, reproducibility, and analytical sensitivity during extended operation and to assess limits of detection and quantification for peptide standards in plasma.

Methodology and Instrumentation

Human plasma was denatured, reduced, alkylated, digested with trypsin, and spiked with a balanced mixture of stable isotope-labeled standard (SIS) peptides. Samples were loaded onto single-use Evotips (1 µg digest per tip) and analyzed using a 21-minute pre-formed gradient on a 100 µm×8 cm C18 column at 1 µL/min, achieving 60 injections per day.

Dynamic multiple reaction monitoring (dMRM) targeted 33 heavy/endogenous peptide pairs (198 transitions) corresponding to 31 protein biomarkers. A robustness test involved 574 consecutive injections of plasma digest spiked with SIS peptides without any system cleaning or tuning over 12 days. Standard curves were generated before and after the robustness sequence, covering on-column peptide amounts from 4 amol to 100 fmol.

Instrument Configuration

• Chromatography: Evosep One with Pepsep trap column (3 µm C18 beads).
• Mass Spectrometer: Agilent 6495 triple quadrupole with nanospray source (nanoESI, positive mode).
• Key Settings: Drying gas 11 L/min at 200 °C, capillary voltage 1750 V, iFunnel voltages 200 V/110 V, cycle time 24 min, dwell times 5.9–80.6 ms.

Key Results and Discussion

Retention time reproducibility across 574 injections showed median RSD below 1% for all targeted peptides. Peak area RSD values had a median of 8.5%, with 94% of peptides under 16% RSD. Four representative biomarkers displayed consistent responses (peak area RSD 6–8%, RT RSD 0.6–1.0%). Column backpressure remained stable, and no system adjustments were required.

Standard curve analyses before and after the 12-day robustness test yielded identical limits of detection (4 amol on column) and quantification (10 amol), with excellent linearity (R2 >0.998) over four orders of magnitude and accuracy within 80–120%. This stability demonstrates that pre-loaded Evotips can retain peptide integrity for at least ten days under refrigerated storage.

Benefits and Practical Applications

• High-throughput quantification of low-abundance plasma proteins with minimal maintenance.
• Robust performance over extended sequences without column cleaning or system tuning.
• Reliable sensitivity down to the amol level suitable for clinical research and biomarker verification.

Future Trends and Opportunities

Emerging applications may include expansion to larger biomarker panels, integration with automated sample preparation workflows, and coupling with orthogonal omics platforms. Advances in gradient pre-formation and disposable trap devices promise further gains in throughput and reproducibility, supporting personalized medicine and high-capacity screening.

Conclusion

The combination of Evosep One and Agilent 6495 triple quadrupole LC/MS provides a highly robust, sensitive, and reproducible platform for targeted protein quantification in plasma. Its capacity for continuous operation without maintenance and consistent analytical performance makes it well suited for high-throughput proteomic studies.

References

• Agilent 6495 Triple Quadrupole LC/MS: Peptide Quantitation Performance. Agilent Technologies Technical Overview, 2016, publication 5991-6898EN.
• Jet Stream Proteomics for Sensitive and Robust Standard Flow LC/MS. Agilent Technologies Technical Overview, 2015, publication 5991-5687EN.
• Bache N et al. A Novel LC System Embeds Analytes in Pre-formed Gradients for Rapid, Ultra-robust Proteomics. Molecular & Cellular Proteomics 2018, 17(11):2284–2296.