MS Identification of Trace level Impurities from a Non-MS Compatible Mobile Phase Using ACQUITY UPLC System with 2D Technology by Heart-cutting and Online Sample Concentration

Importance of the Topic

Pharmaceutical and environmental analyses frequently rely on orthophosphoric acid or other nonvolatile buffers for optimal UV performance, preventing direct coupling to mass spectrometry. Two-dimensional liquid chromatography (2D-LC) with heart-cutting and online sample concentration overcomes this limitation, enabling mass spectral characterization of trace impurities without modifying existing non-MS methods.

Objectives and Study Overview

This application note demonstrates how an ACQUITY UPLC system configured for heart-cutting 2D-LC, combined with at-column dilution and a trap cartridge, can capture and concentrate targeted peaks from a non-MS-compatible first-dimension method and transfer them to a second-dimension MS-compatible separation for mass spectral identification of trace-level impurities.

Methodology and Instrumentation

• First dimension: ACQUITY UPLC HSS C18 column with 0.1 % orthophosphoric acid/ACN gradient, UV detection at 210 nm, 15 min runtime.
• Heart-cutting: Two 2-position, 6-port valves divert the fraction of interest into an Oasis HLB trap cartridge while an at-column dilution pump reduces organic content and retains analytes.
• Sample stacking: Three sequential injections accumulate the analyte band on the trap for enhanced sensitivity.
• Second dimension: ACQUITY UPLC CSH C18 column with water/ACN mobile phase at 0.6 mL/min, back-flush elution of the trap cartridge, coupled to a Xevo TQD mass spectrometer operating in full-scan ESI(+) and ESI(–) modes.
• Control and data management: MassLynx v4.1 orchestrates valve events, dilution, trapping, and MS acquisition.

Key Results and Discussion

• First-dimension UV runs identified target impurity retention times (~9.54 min, ~10.39 min).
• Heart-cut reproducibility over three injections demonstrated consistent peak stacking on the trap cartridge.
• Blank-corrected second-dimension UV chromatograms confirmed selective transfer and effective removal of nonvolatile buffer.
• Full-scan MS spectra from the Xevo TQD provided clear molecular ion peaks and fragment patterns, enabling confident impurity identification.

Benefits and Practical Applications

• Direct MS analysis of non-MS-compatible HPLC methods without method redevelopment or offline fraction collection.
• Online sample concentration significantly improves sensitivity for trace-level impurity detection.
• Independent second-dimension method runtime allows higher resolution and increased sensitivity.

Future Trends and Applications

Emerging valve designs, advanced trap chemistries, and automation will further streamline 2D-LC–MS workflows. Coupling with high-resolution mass spectrometry and AI-guided data analysis holds promise for rapid impurity profiling in complex matrices and regulatory compliance.

Conclusion

Heart-cutting 2D UPLC–MS with at-column dilution and online sample concentration offers a robust solution for identifying trace impurities from non-MS-compatible methods. This approach minimizes sample handling, enhances sensitivity, and delivers straightforward data interpretation for quality control and research laboratories.

References

• Root DS, Wheat TE, McConville P. Routine MS Detection for USP Chromatographic Methods. Waters Corp. Application Note. 2015.