Minimizing Sample Carryover Using the Multiwash Function of the Agilent 1290 Infinity II Multisampler

Significance of the Topic

Sample carryover in LC-MS can compromise data integrity and reduce laboratory throughput. The Agilent 1290 Infinity II multisampler with multiwash offers an integrated solution to clean both needle exterior and seat, ensuring ultralow carryover and reliable results.

Objectives and Study Overview

This study evaluates the multiwash function of the Agilent 1290 Infinity II multisampler for minimizing carryover of caffeine and a diverse pesticide mixture at 100 000 µg/L concentrations when coupled to an Agilent 6490 triple quadrupole mass spectrometer. Key aims include:

• Quantifying caffeine carryover after a high-concentration injection
• Optimizing multiwash protocols for pesticide analyses
• Identifying primary sources of carryover within the LC-MS system

Methodology and Instrumentation

The analytical system comprised an Agilent 1290 Infinity II high-speed pump, 40 µL multisampler with multiwash, multicolumn thermostat, 2-position switching valve, diode array detector, and an Agilent 6490 triple quadrupole MS with JetStream source. Data acquisition and optimization used the Agilent MassHunter suite. Methods included:

• Caffeine analysis on ZORBAX Eclipse Plus C18 (2.1×50 mm, 1.8 µm), isocratic 11 % acetonitrile/0.1 % formic acid, 0.5 mL/min, 1 µL injection, 50 °C.
• Pesticide gradient from 5 % to 95 % methanol over 11 min, same column, 0.5 mL/min, 1 µL injection, room temperature.
• Multiwash sequence for pesticides: isopropanol+0.1 % formic acid (5 s), acetonitrile+0.1 % formic acid (5 s), water+0.1 % formic acid (20 s), applied to both needle wash and seat backflush.

Main Results and Discussion

• Caffeine carryover after a 100 000 µg/L injection was 4.5 ppm, falling below detection after three blank injections.
• Pesticide carryover for 13 compounds was under 9 ppm for most analytes using the optimized multiwash protocol; pyraclostrobin and thiabendazole required extra blanks for complete removal.
• Alternating column regeneration and manual column swaps revealed the analytical column as the main carryover source (up to 170 ppm), while the multisampler contributed under 9 ppm and the switching valve up to 11 ppm.
• Proper fitting installation, extended gradient hold, and alternating column strategies effectively minimize carryover artifacts.

Benefits and Practical Applications

• Ultralow carryover enhances trace analysis accuracy and prevents false positives.
• Reduced blank requirements increase sample throughput and operational efficiency.
• Applicable across environmental, food safety, pharmaceutical, and bioanalytical workflows demanding stringent carryover control.

Future Trends and Applications

• Integration with automated column switching and inline dilution for expanded dynamic ranges.
• Custom multiwash protocols for challenging polar or high-throughput applications.
• Predictive carryover management using software algorithms based on solvent and analyte properties.

Conclusion

The Agilent 1290 Infinity II multisampler’s multiwash function delivers ultralow carryover for high-concentration injections by combining programmable solvent washes and backflush. Coupled with column management strategies, this approach significantly improves LC-MS reliability and throughput.

References

1. Dolan J W Attacking Carryover Problems LCGC 2001 19(10)
2. Schuhn B Tips and Tricks for Achieving Near-Zero Carryover Using the Multiwash Function of the Agilent 1290 Infinity II Multisampler Agilent Application Note 5991-6051EN 2015
3. Huesgen A G Naegele E Automated Alternating Column Regeneration on the Agilent 1290 Infinity LC Agilent Application Note 5990-5069EN 2009