Increasing sensitivity in peptide-level studies; Cyclic ECD product ions

Significance of the topic

Peptide-level tandem mass spectrometry (MS/MS) is central to proteomics and biotherapeutic characterization because it enables confident protein identification and localization of post-translational modifications (PTMs). However, many peptides—especially low-abundance species and singly charged fragments—produce weak product ion signals that limit sequence coverage and confidence. Enhancing sensitivity across a broad m/z range without compromising spectral information is therefore a high priority for workflows such as peptide mapping, PTM localization and de novo sequencing. The Wideband Enhancement (WBE) approach implemented on the Cyclic IMS P20 mass spectrometer addresses this need by increasing TOF duty cycle selectively across mobility-separated ions, improving detection of low-intensity CID and ECD fragments.

Objectives and study overview

The study evaluates Wideband Enhancement (WBE) on a Cyclic IMS P20 platform to determine how synchronizing TOF pusher pulses with ion mobility elution improves fragment ion signal intensity for both collision-induced dissociation (CID) and electron-capture dissociation (ECD) peptide MS/MS. Key aims were to optimize cyclic ion mobility parameters, quantify signal gains across a wide m/z range, demonstrate benefits for peptide mapping (including a monoclonal antibody digest), and assess WBE performance in both CID and ECD acquisition modes.

Methodology

Experiments combined liquid chromatography, cyclic ion mobility separation and TOF MS with optional ECD placed before the mobility cell. The principal concept is Enhanced Duty Cycle (EDC): pulsing ions into the TOF pusher region in synchronization with the arrival time of mobility-resolved ion packets to raise the effective duty cycle for target m/z windows. Because ion mobility correlates broadly with m/z (lower m/z -> higher mobility -> earlier arrival), the instrument can sweep the EDC enhancement window in concert with mobility elution to provide continuous sensitivity improvement across a broad mass range, a mode termed Wideband Enhancement (WBE). WBE was tested in single-pass ion mobility separations and in an MSE-like acquisition to boost sensitivity of high-energy channels.

Used instrumentation

• Chromatography: ACQUITY Premier Binary UPLC with ACQUITY Premier Peptide BEH 130 Å, 1.7 μm, 2.1 × 100 mm column.
• Mass spectrometry: Cyclic IMS P20 mass spectrometer with high-resolution cyclic ion mobility separator and TOF analyzer (~100,000 resolving power FWHM). A Waters electron-capture dissociation (ECD) cell was installed in the pre-IMS position.
• Software: Data acquired in MassLynx v4.2 and processed using peptide mapping and top-down workflows in waters_connect UNIFI.
• Samples: Glu-fibrinopeptide B (100 fmol/μL), Substance P (250 fmol/μL), and a monoclonal antibody (mAb) tryptic digest standard.

Main results and discussion

WBE produced substantial increases in product ion intensities for both CID and ECD MS/MS across the tested m/z ranges. Highlights include:

• Glu-fibrinopeptide B CID spectra showed signal increases up to ~20-fold for selected product ions across 200–2000 m/z when WBE was enabled, with clear enhancement of ions such as m/z 813.39.
• ECD product ions of Substance P displayed average enhancements of approximately 10-fold across 496–1348 m/z, improving coverage of ECD-specific fragments (including w-type ions).
• In peptide mapping of an mAb tryptic digest, low-intensity product ions—particularly from singly charged precursors—were markedly amplified. The T35 peptide from the heavy chain exhibited >10× intensity increase for low-mass fragments, enabling confident sequence assignment.
• Applying WBE in an MSE-like high-energy channel improved sequence coverage when processed in waters_connect, demonstrating compatibility with data-independent-like acquisition approaches.
• Enhanced ECD sensitivity allowed distinguishing isobaric amino acids (leucine vs isoleucine) by resolving characteristic neutral-loss-derived w ions that were previously too weak to detect reliably.

The results indicate that by exploiting the mobility–m/z relationship and scanning the EDC window with ion arrival time, WBE raises effective TOF duty cycle for a wide mass band without requiring instrument hardware changes to the analyzer itself. This improves detection of low-abundance fragments while preserving the information content of both CID and ECD spectra.

Benefits and practical applications

Practical advantages demonstrated or implied by the study:

• Increased sensitivity for low-abundance peptide fragments improves sequence coverage and confidence in peptide mapping and PTM localization—critical for biotherapeutic characterization and regulatory submissions.
• Enhanced ECD performance enables complementary fragmentation pathways to CID to be used more routinely, expanding capability for labile PTM retention and residue-level isomer discrimination.
• Compatibility with MSE-like and targeted MS/MS workflows supports both discovery and targeted applications, including characterization of mAbs and other complex biologics.
• Potential to reduce sample amount or injection load required to achieve acceptable coverage, increasing throughput or enabling analysis of scarce samples.

Future trends and potential applications

Potential directions and opportunities arising from WBE-enabled mobility–TOF operation include:

• Broader adoption in routine peptide-mapping pipelines and regulated environments to increase robustness of low-abundance peptide detection.
• Extension to top-down and middle-down proteomics where fragment sensitivity limits sequence coverage of large proteoforms.
• Integration with data-independent acquisition (DIA) and advanced acquisition schemes to combine wideband sensitivity gains with comprehensive sampling strategies.
• Automation and optimization of WBE window scanning strategies via instrument control software to tailor enhancement profiles for specific mass ranges or sample types.
• Combination with orthogonal ion selection/filters (e.g., FAIMS) for further background suppression and sensitivity improvements.
• Systematic evaluation of WBE effects on quantitative performance, spectral quality metrics, false-discovery rates and downstream bioinformatics workflows.

Conclusion

Wideband Enhancement (WBE) on the Cyclic IMS P20 platform leverages the correlation between ion mobility and m/z to synchronize TOF pusher pulses with mobility-resolved arrivals, increasing the effective duty cycle and substantially boosting product ion signals for CID and ECD MS/MS. The approach yields up to ~20-fold gains for CID and ~10-fold for ECD in tested ranges, markedly improving detection of low-abundance fragments and enabling enhanced peptide mapping performance, including improved ECD-derived residue discrimination. WBE is therefore a practical and impactful enhancement for proteomic and biotherapeutic characterization workflows.

References

1. Cooper-Shepherd DA, Jones IA, Marsden-Edwards E, Rabbani R. Increasing sensitivity in peptide-level studies; Cyclic ECD product ions. Waters Corporation poster; Cyclic IMS P20 Mass Spectrometer evaluation, 2026.