Tips and Tricks for Achieving Near-Zero Carryover Using the Multiwash Function of the Agilent 1290 Infinity II Multisampler

Importance of the topic

Reducing sample carryover and cross-contamination is critical to ensure accuracy and reproducibility in liquid chromatography and LC/MS analyses. Carryover can lead to ghost peaks, distorted quantification, and compromised data integrity, especially in trace analysis and regulated environments. The Agilent 1290 Infinity II Multisampler with its multiwash function provides a targeted solution to minimize carryover to near-zero levels.

Goals and Study Overview

This technical overview outlines strategies and best practices for utilizing the multiwash function of the Agilent 1290 Infinity II Multisampler. The primary objective is to optimize wash protocols, solvent selection, and cycle settings to achieve less than 10 parts per million carryover or eliminate it entirely without compromising chromatographic performance.

Methodology and Instrumentation

The multiwash approach leverages a flow-through needle design and multiple wash options:

• Internal needle wash to purge the fluid path.
• External needle wash using up to three solvents in a flush port.
• Needle seat backflush with a high-pressure pump to clean the seat capillary.
• Injection valve cleaning for the flow path and valve internals.

A peristaltic pump delivers fresh wash solvents, and an integrated high-pressure pump enables seat backflush. Users can define up to four sequential wash steps, assign three solvents, and set individual durations. Optimal settings include a weak solvent step matching the initial gradient as the final wash to preserve peak shape, and a strong solvent step of at least the final gradient strength. Typical wash times around five seconds per solvent, combined with the “Start Conditions” function, ensure complete solvent exchange and system readiness.

Instrumentation Used

• Agilent 1290 Infinity II Multisampler with multiwash option
• Piezo peristaltic pump for solvent delivery
• Integrated high-pressure flush pump for seat backflush

Main Results and Discussion

Using the multiwash function with properly sequenced solvents and durations, carryover was reproducibly reduced below 10 ppm. Key observations include:

• Layering effects in delivery tubing are mitigated by short wash cycles followed by “Start Conditions” to flush all solvents through the system.
• Weak wash solvents matching the initial gradient prevent peak shape deterioration when returning to analytical flow.
• Strong solvents at or above final gradient composition are effective at removing strongly retained compounds.
• Proper gradient design and maintenance of capillary connections are essential to isolate the autosampler as the primary carryover source.

Benefits and Practical Applications

• Significantly improved reproducibility and data quality in trace analysis.
• Reduced need for manual cleaning interventions and downtime.
• Enhanced throughput and productivity in high-throughput laboratories.
• Applicable across pharmaceutical, environmental, and food testing where low carryover is critical.

Future Trends and Opportunities

Advancements may include automated method development guided by machine learning to predict optimal wash sequences, integration of online monitoring for real-time carryover detection, expanded solvent libraries for specialized applications, and improvements in material coatings to further reduce adsorption. Such developments will drive broader adoption in regulatory and high-throughput settings.

Conclusion

The multiwash function of the Agilent 1290 Infinity II Multisampler delivers a robust solution for achieving near-zero sample carryover. By tailoring wash solvents, sequence, and durations, users can ensure high data integrity and reliable workflow performance. Adherence to best practices in solvent compatibility, gradient design, and regular auto-clean cycles is essential for optimal results.

Reference

• Agilent 1290 Infinity Multisampler User Manual, Agilent Technologies, publication number G7167-90000, 2014.