Reducing carryover in high-sensitivity low-flow LC-MS analysis: the comprehensive study of multi-wash, ZebraWash, and large volume injections

Significance of the Topic

Reducing carryover in low-flow LC-MS proteomics is critical to ensure accurate and reproducible quantification of peptides and proteins, particularly when handling samples with trace amounts of analytes. Inefficient cleaning between injections can bias results and hinder high-throughput operation.

Objectives and Study Overview

This study aimed to evaluate the ZebraWash procedure integrated into the Thermo Scientific Vanquish Neo UHPLC system for its ability to minimize trap column carryover in nanoLC-MS workflows and to assess the performance of large-volume multi-draw injections up to 500 µL without sample loss.

Methodology and Instrumentation

• Sample preparation: HeLa Digest combined with PRTC standard, reconstituted in 0.1% formic acid and sonicated.
• Chromatography and MS: Thermo Scientific Vanquish Neo UHPLC with EASY-Spray PepMap Neo nano column and Acclaim PepMap C18 separation column; Orbitrap Exploris 480 mass spectrometer operating in data-dependent acquisition.
• Trap-and-elute workflow: Evaluation of Fast Wash versus ZebraWash cycles (2, 4, 8, 16) for trap cleaning.
• Large-volume injections: Multi-draw injections of up to 500 µL using aqueous TFA loading buffer to prevent peptide losses.
• Data analysis: Proteome Discoverer 2.5 with SEQUEST HT, INFERYS rescoring, FDR below 1%; further processing in R.

Main Results and Discussion

ZebraWash achieved ultra-low trap column carryover (<0.004%) independent of injection amount when using 16 cycles with a 100 µL loop. Four ZebraWash cycles delivered more effective cleaning than the standard Fast Wash procedure at equivalent solvent volumes. Separation column overloading became the dominant source of residual carryover at higher sample loads (up to 4,000 ng). Multi-draw injections using diluted samples (2 ng/µL, 500 µL) yielded comparable signal intensities, peptide identifications, and chromatographic profiles to concentrated injections (200 ng/µL, 5 µL), demonstrating reliable load transfer and quantitative reproducibility.

Benefits and Practical Applications

• Enhanced data quality by minimizing trap column memory effects.
• Increased throughput through parallel and automated cleaning of trap and separation columns without blank runs.
• Flexible injection volumes enabling direct analysis of dilute samples post-immunoprecipitation or extraction without lyophilization.
• Consistent quantitative performance supports robust proteomic quantitation in research and quality control laboratories.

Future Trends and Potential Applications

Further optimization of ZebraWash parameters and loop sizes may enable even faster cycle times and reduced solvent consumption. Integration with high-throughput clinical and biopharmaceutical workflows could expand applications to biomarker validation and therapeutic monitoring. Advances in column chemistries and automated fluidics may further mitigate separation column carryover and support emerging single-cell proteomics.

Conclusion

The ZebraWash procedure on the Vanquish Neo UHPLC system represents a significant improvement in trap column cleaning for low-flow LC-MS proteomics, delivering minimal carryover and high reproducibility. Coupled with large-volume multi-draw injections, this workflow enhances throughput and analytical confidence for complex proteomic analyses.