A novel 75 cm column size gives increased resolution and better sequence coverage

Significance of the Topic

The effective separation and identification of complex peptide mixtures is fundamental to bottom-up proteomics. High chromatographic resolution increases peak capacity, sensitivity, and sequence coverage, enabling deeper proteome profiling and confident detection of post-translational modifications.

Objectives and Study Overview

This study evaluated the performance of a novel 75 cm EASY-Spray™ Acclaim™ PepMap™ C18 column against a standard 50 cm format. Using a HeLa cell digest spiked with a peptide retention time calibration (PRTC) mixture, extended gradients were applied to compare peak capacity, resolution, peptide identification rates, and sequence coverage between the two column lengths.

Methodology and Instrumentation

Samples were analyzed on a Thermo Scientific™ EASY-nLC™ 1200 system coupled to a Q Exactive™ Hybrid Quadrupole-Orbitrap mass spectrometer.

• Columns: 75 μm i.d. × 75 cm and 75 μm i.d. × 50 cm EASY-Spray Acclaim PepMap C18 (2 μm, 100 Å)
• Mobile phases: A = water + 0.1% formic acid; B = 80:20 acetonitrile/water + 0.1% formic acid
• Gradient: extended 500 min ramp from 5% to 95% B at 200 nL/min
• MS settings: full MS at 60 000 resolution (m/z 350–1200), data-dependent MS/MS at 15 000 resolution, HCD fragmentation, dynamic exclusion 20 s
• Data processing: Proteome Discoverer™ 2.1 with SEQUEST® HT, human SwissProt database, trypsin digestion, oxidation (M) and deamidation (N) dynamic modifications, carbamidomethyl (C) static

Main Results and Discussion

The 75 cm column operated at 600–700 bar versus 450–500 bar for the 50 cm at 200 nL/min. Key findings:

• Peptide spectral matches increased by 43.4% (170 574 vs 118 050)
• Distinct peptide groups rose by 25.7% (40 230 vs 32 013)
• Protein identifications improved by 5.0% (5 070 vs 4 828)
• Peak widths at half height (PWHH) for three PRTC peptides decreased from ~33–42 s to ~24–33 s
• Retention time shifts over 500 min showed RSD < 0.4% (≤1.5 min)
• Calculated peak capacity (Cp) increased from ~800 to ~1 050 for the 75 cm column

Benefits and Practical Applications

The extended 75 cm column offers greater separation efficiency, enhanced sensitivity, and deeper proteome coverage without substantially altering retention times. These improvements support robust identification of low-abundance peptides and detailed characterization workflows in academic and industrial proteomics, QA/QC, and biomarker discovery.

Future Trends and Applications

Emerging directions include further scaling of column length with ultra-high-pressure systems, integration of higher-performance mass analyzers, microflow-based platforms for throughput, and advanced data analysis algorithms for real-time identification. Such developments will expand applications in clinical proteomics, systems biology, and precision medicine.

Conclusions

The 75 cm EASY-Spray Acclaim PepMap C18 column delivers significantly improved peak capacity and identification metrics compared to the 50 cm format. It maintains stable retention times and operates within the pressure limits of modern nanoLC systems, offering a practical route to deeper, more reliable proteome analyses.

Instrument Used

• Thermo Scientific™ EASY-nLC™ 1200 system
• Thermo Scientific™ EASY-Spray™ Acclaim™ PepMap™ C18 columns (75 cm and 50 cm)
• Thermo Scientific™ Q Exactive™ Hybrid Quadrupole-Orbitrap mass spectrometer
• Proteome Discoverer™ 2.1 software

References

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