Comparison of Drift-tube Ion Mobility and Structures for Lossless Ion Manipulation(SLIM) for the Characterization of Polysorbate, Polyethers, Surfactants Compounds

Significance of the Topic

Excipients such as polysorbates and polyethers are indispensable in biotherapeutic production, improving solubility, controlling pH, extending shelf-life, and stabilizing protein and vaccine conformations. Impurities or degradation products in these polymers can adversely affect drug stability and safety. Conventional liquid chromatography–mass spectrometry often fails to fully resolve the complex mixture of isobaric and isomeric oligomers, leading to incomplete characterization.

Objectives and Study Overview

This study compares two high-resolution ion mobility–mass spectrometry platforms for detailed analysis of commercially sourced polysorbates, polyethers, and related surfactants: the Agilent 6560 Drift-Tube IM-Q-TOF employing multiplexed demultiplexing, and a SLIM-based HRIM device coupled to an Agilent 6546 LC/Q-TOF. The goal is to evaluate their ability to separate co-eluting isobaric and isomeric oligomers using rapid analyses with minimal chromatographic gradients.

Methodology

Samples of commercial polysorbates, polyethers, and surfactants were prepared at 1 mg/mL. Two parallel workflows were used:

• Drift-Tube IM-Q-TOF: m/z range 100–1700, optimized drift voltage and funnel RF settings, data acquired with 4-bit multiplexing (3.9 ms fill, 300 ms release).
• SLIM-HRIM: m/z range 300–3200, traveling-wave parameters adjusted for optimal ion trapping and release.

Chromatography was minimized to a 3-minute gradient on an Agilent RRHD EC-C18 column (2.1×100 mm, 1.9 µm) at 45 °C, with water/methanol (2.5 mM NH4 formate, 0.05% formic acid) from 10% to 100% B in 3 minutes and a 4-minute hold at 0.4 mL/min. Both direct infusion (flow injection) and rapid LC runs were performed.

Used Instrumentation

• Agilent 6560 Drift-Tube IM Q-TOF with high-resolution demultiplexing.
• SLIM-based MOBIE HRIM device coupled to Agilent 6546 LC/Q-TOF.
• Agilent Jet Stream ESI source in positive ion mode.
• RRHD 2.1×100 mm, 1.9 µm EC-C18 column.

Main Results and Discussion

The two platforms demonstrated complementary strengths:

• Flow-injection spectra revealed repeating 44 Da intervals and overlapping PEG sorbitan esters; HRIM resolved isobaric peaks at m/z 1150 and 1168.
• Drift-tube trend-line plots separated modified PEG sorbitan components by collision cross section.
• SLIM-HRIM achieved clear separation of isobaric PEG dimethyl ether and PEG diacid oligomers by drift time.
• Isomeric pairs (PEG diglycidyl ether vs. PEG methacrylate) were distinguished for shorter chains (n<9); longer chains converged in drift spectra.
• High-resolution demultiplexing (HRdm) enhanced drift separation of closely spaced oligomers.
• 4D feature extraction (drift time, retention time, m/z, intensity) enabled identification of minor impurities such as PEG and PEG dimethacrylate in surfactant standards.

Benefits and Practical Applications

High-resolution IM-MS approaches deliver:

• Separation of co-eluting isobaric and isomeric species without lengthy LC gradients.
• Rapid screening workflows (3–5 min) for QA/QC of polymeric excipients.
• Detection of low-level impurities or degradants in complex matrices.
• Improved compound identification through collision cross section measurements.

Future Trends and Possibilities

Emerging directions include:

• Integration of HRIM into routine QA/QC pipelines for biologics manufacturing.
• Development of standardized CCS libraries for excipient characterization.
• Expansion to other complex polymeric and lipid excipients.
• Advances in SLIM architectures for longer path lengths and ultrahigh resolution.
• Machine-learning algorithms for automated deconvolution of 4D datasets.

Conclusion

Both drift-tube and SLIM-based HRIM platforms offer significant enhancements in separating isobaric and isomeric surfactant oligomers, reducing chromatographic demands, and detecting minor impurities. Their adoption can streamline excipient characterization in biotherapeutic development, quality control, and regulatory compliance.