The Lowesr Near Zero Carryover

Importance of Ultra-Low Carryover

In trace analysis, even minute sample remnants can distort peak identification, create ghost peaks and impair detection limits. Achieving near-zero carryover enhances data integrity and operational efficiency, particularly in high-throughput QA/QC, environmental screening and biomarker studies.

Study Objectives and Overview

This application sheet evaluates the carryover performance of the Nexera autosampler in three scenarios: caffeine analysis by UHPLC-UV, carryover testing with the highly adsorptive compound chlorhexidine, and trace amine analysis (Desipramine and Amytriptyline) using single-quadrupole LC–MS. Each experiment measures residual contamination following sequential blank injections under varying rinse protocols.

Methodology

The rinse protocol combined multiple cleaning steps to minimize contamination:

• Injection port rinse
• Needle outer-surface flush
• Needle inner-surface rinse
• Needle dip rinse
• Needle pump rinse

Sample concentrations were set at 4 g/L for caffeine, 2 g/L for chlorhexidine and 5 mg/L for each amine. Blanks were injected post-sample to detect residual peaks.

Used Instrumentation

• UHPLC system with Nexera SIL-30AC autosampler
• Reversed-phase ODS column (2.0 mm ID×100 mm, 1.8 µm) at 40 °C (caffeine) or 30 °C (chlorhexidine)
• Mobile phase methanol:water (20:80), flow 0.4 mL/min
• UV detection at 272 nm, operating pressure up to 100 MPa
• Single-quadrupole LCMS-2020-ESI(+) with ODS column (2.1 mm ID×100 mm, 1.8 µm) for amine analysis
• Gradient elution (25→50→90→25% B) using 0.1% formic acid and acetonitrile/water (25:75); flow 1.5 mL/min, column at 40 °C
• Rinse solutions: 0.05–0.1% formic acid in methanol or acetonitrile as specified for each rinse step

Main Results and Discussion

Caffeine carryover was reduced to 0.0004% after the first blank and became undetectable in the second. Chlorhexidine residues fell below the detection limit (<0.003%) when full rinse protocols were applied. In LC–MS tests, combining dip, pump, internal and port rinses eliminated Desipramine and Amytriptyline to below 0.0042% and 0.0027% respectively; omitting rinses resulted in up to 0.05% residual signal.

Benefits and Practical Applications

The multi-step rinse architecture of the Nexera autosampler ensures ultra-low carryover without extensive manual cleaning, streamlining high-throughput workflows, reducing false positives and lowering solvent usage.

Future Trends and Possibilities

Advancements may include adaptive rinse solvent selection based on analyte chemistry, real-time rinse optimization via machine learning and integration of in-line diagnostic sensors to further push carryover towards true zero.

Conclusion

The combination of optimized fluidics and comprehensive rinse strategies in the Nexera autosampler achieves near-zero carryover across diverse compound classes, significantly enhancing reliability in trace-level analyses.

Reference

• Nexera Application Data Sheet No.4 (LAAN-A-LC-E228), Shimadzu Corporation, Issued October 2010