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

Importance of the Topic

The rapid growth in mass detector sensitivity for liquid chromatography has increased the risk of sample carryover, which can compromise quantitative accuracy and sample integrity. Effective mitigation strategies are essential for high-throughput laboratories and regulatory environments where trace-level detection is critical.

Study Objectives and Overview

This study evaluated how needle wash solvent composition and autosampler wash modes impact carryover in a UPLC–MS setup. Granisetron HCl was chosen as a model compound to quantify carryover down to 0.0002% (2 pg on column). The ACQUITY UPLC H-Class PLUS with QDa mass detector and an ACQUITY Diverter Valve was used to protect the detector from high-concentration injections.

Methodology and Instrumentation

The system configuration included:

• UPLC HSS T3 column (3.0 × 50 mm, 1.8 µm) at 35 °C
• Mobile phase: 0.1% formic acid in water (A) and acetonitrile (B) at an 80:20 isocratic ratio
• Flow rate: 0.9 mL/min, injection volume: 1 µL, run time: 3 min
• Needle wash solvents tested: water/acetonitrile (90:10, 50:50), water/methanol (90:10, 50:50), 100% acetonitrile, 100% methanol
• Wash modes: default (6 s post-injection), 6 s pre- and post-injection, 12 s pre- and post-injection
• Quantitation: three-point calibration at 2, 5 and 10 pg, diverted to waste during high-concentration injection

Main Results and Discussion

• 100% organic wash solvents showed higher carryover, indicating incomplete removal of Granisetron HCl.
• A 50/50 water:acetonitrile mixture provided the lowest carryover among solvents tested.
• Extending wash cycles to 12 s pre- and post-injection reduced carryover by approximately threefold compared with the default mode.
• The flow-through-needle design and dedicated wash pump prevented cross-contamination between wash solvent and sample stream, enhancing cleaning efficiency.

Benefits and Practical Applications

• Improved quantitation reliability at trace levels through optimized wash chemistry and timing.
• Flexibility to tailor needle wash composition independently from the mobile phase.
• Enhanced throughput with minimal additional cycle time by selecting appropriate wash modes.
• Applicability across a broad range of reverse-phase methods requiring low carryover.

Future Trends and Applications

• Development of automated wash-optimization tools within instrument software.
• Integration of intelligent wash solvent selection based on analyte properties.
• Expansion of carryover mitigation strategies to multi-dimensional separations and high-pressure systems.

Conclusion

Optimizing needle wash solvent composition and autosampler wash parameters is critical for minimizing carryover in high-sensitivity LC–MS analyses. A balanced water:acetonitrile wash and extended wash durations effectively reduce residual contamination, supporting robust quantitative performance.

Reference

1. DesJardins C., Li Z., McConville P. Carryover Mitigation Using Needle Wash Solvent Chemistry and Autosampler Features of a UPLC–MS System. Waters Corp.; 2019.
2. Waters ACQUITY UPLC H-Class PLUS System Guide. Waters Corporation; 2018.
3. Dolan J. Autosampler Carryover. LCGC Europe. 2006;19(10):522–529.
4. Waters ACQUITY UPLC Sample Manager–Flow Through Needle PLUS Series Overview and Maintenance Guide. Waters Corporation; 2018.
5. O’Neil MJ, ed. The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. 14th ed. Merck; 2006.