CARRYOVER MITIGATION USING NEEDLE WASH SOLVENT CHEMISTRY AND AUTOSAMPLER FEATURES OF A UPLC-MS SYSTEM

Importance of the Topic

Mass spectrometry detection increases sensitivity in liquid chromatography applications and demands effective strategies to minimize sample carryover. Carryover can compromise quantitative accuracy, reduce throughput, and lead to false positives, especially in bioanalytical and pharmaceutical analyses. Optimizing autosampler needle wash protocols and wash solvent composition is therefore critical to ensure robust, reliable results.

Objectives and Study Overview

This study aimed to evaluate the effects of needle wash solvent chemistry and autosampler wash modes on carryover levels in a UPLC-MS system. Granisetron HCl was selected as a model compound. The work focused on quantifying carryover to levels as low as 0.0002% (2 pg on-column) and comparing various wash solvent compositions and wash durations using a modern UPLC H-Class PLUS system with a QDa mass detector and diverter valve.

Methodology and Instrumentation

• Instrumentation: ACQUITY UPLC H-Class PLUS system, ACQUITY QDa mass detector, ACQUITY Diverter Valve, UPLC HSS T3 column (1.8 µm, 3.0 × 50 mm).
• Chromatographic conditions: 35 °C column temperature, 15 °C sample temperature, 1 µL injection volume, 0.9 mL/min flow rate, isocratic elution (80:20 water:acetonitrile with 0.1% formic acid) over 3 minutes, SIR at m/z 313.1.
• Wash solvents tested: water:acetonitrile (90:10, 50:50), water:methanol (90:10, 50:50), 100% acetonitrile, 100% methanol.
• Needle wash modes: default 6 seconds post-injection, 6 seconds pre- and post-injection, 12 seconds pre- and post-injection.
• Carryover quantification: three-point calibration (2, 5, 10 pg on-column), calculation of carryover percentage from post-challenge blank concentrations.

Results and Discussion

• Acetonitrile-based wash solvents generally outperformed methanol-based formulations in reducing carryover.
• Increasing organic content in the wash solvent improved removal of granisetron residues from the needle surface.
• Extending wash mode duration (pre- and post-injection rinses) decreased carryover by up to threefold compared to the default 6-second rinse.
• The diverter valve effectively directed high-concentration injections to waste, preventing detector saturation and ensuring accurate quantitation.

Benefits and Practical Applications

Optimizing needle wash protocols and solvent composition enhances data quality by minimizing carryover, improving reproducibility, and safeguarding against cross-contamination. This approach benefits pharmaceutical, clinical, and environmental analyses where trace-level detection and high throughput are essential.

Future Trends and Potential Applications

Anticipated developments include advanced autosampler designs with programmable multi-step washing cycles, tailored solvent gradients for specific analyte classes, and integration of real-time carryover monitoring. Continued innovation in solvent formulations and hardware refinements will further reduce carryover and speed method development.

Conclusion

Effective carryover mitigation in UPLC-MS requires a tailored combination of wash solvent chemistry and autosampler wash settings. This study demonstrated substantial improvements in carryover reduction by selecting appropriate solvent mixtures and extending wash durations, ensuring reliable quantitation for sensitive analyses.

References

1. DesJardins C, Li Z, McConville P. ACQUITY UPLC H-Class PLUS System with QDa Mass Detector Configuration, Waters Corporation, 2019.
2. Dolan J. Autosampler carryover. LCGC Europe, 2019;19(10):522–529.
3. Dolan J, Cooley L. Reproducibility and carryover – A case study. LCGC, 2001;19(3):290–296.
4. Waters Corporation. ACQUITY UPLC Sample Manager Guide, 2018.
5. Waters Corporation. Solvent Considerations for UPLC Systems, 2018.