Simultaneous high-performance and ultra-highperformance liquid chromatographic analysis of acetaminophen impurities using a single instrument

Importance of the Topic

Contemporary analytical laboratories demand high sample throughput and efficient use of instrument footprint. Dual liquid chromatography systems combining HPLC and UHPLC channels in one instrument enable parallel operation of legacy and fast methods, reducing solvent consumption, analysis time and cost while maximizing equipment utilization.

Objectives and Study Overview

This work evaluates the Thermo Scientific Vanquish Flex Duo system for Dual LC by running an established HPLC assay for acetaminophen impurities alongside its accelerated UHPLC counterpart on the same instrument. The goal is to demonstrate simultaneous method execution, performance equivalence and resource savings.

Methodology and Instrumentation

The Vanquish Flex Duo platform features two independent flow paths in a single footprint. Sample preparation involved stock solutions of acetaminophen and its impurities in methanol, diluted to 10 mg/mL API and 0.1 percent impurities.

• HPLC channel: Hypersil GOLD C8 column 4.6 x 100 mm 3 microns; phosphate buffer and methanol mobile phase; flow rate 1 mL per minute; gradient from 1 to 85 percent organic over 4 minutes.
• UHPLC channel: Hypersil GOLD C8 column 2.1 x 100 mm 1.9 microns; same solvents; flow rate 0.5 mL per minute; gradient accelerated by Chromeleon CDS UHPLC speed-up tool.
• Detectors: two variable wavelength detectors with flow cells of 11 microliters and 2.5 microliters operated at 230 nanometers.
• Data acquisition by Chromeleon CDS version 7.2.8.

Main Results and Discussion

Both channels achieved baseline separation of acetaminophen and five impurities, meeting USP resolution requirements. Retention times and precision were comparable, with relative standard deviations below 0.1 percent. The UHPLC path showed reduced injection volumes and shorter cycle times but initially lower signal to noise due to smaller flow cell path length and microvolume injections. Increasing injection volume to 0.5 microliters restored area precision and signal to noise to levels comparable to HPLC. Removing the initial isocratic segment further reduced UHPLC cycle time from 6 to 4.8 minutes without sacrificing resolution.

Benefits and Practical Applications

Optimization of the UHPLC method yielded a 2.5 fold increase in throughput, 50 percent reduction in sample volume, 80 percent reduction in solvent use and 60 percent shorter analysis time compared to the HPLC assay. This translates into potential analysis of 100 samples in a single eight hour shift versus more than 20 hours by HPLC. Estimated solvent cost savings amount to 27 US dollars per 100 samples and over 5400 US dollars per year for 20,000 samples.

Future Trends and Opportunities

Further enhancements may include use of high pressure mixing pumps to minimize gradient delay volumes and equilibration times, increased automation in sample handling, and integration of predictive software tools for method transfer. The dual channel concept supports greener analytical workflows and maximizes instrument productivity in regulated and high throughput environments.

Conclusion

The Vanquish Flex Duo system for Dual LC successfully combines HPLC and UHPLC methods on one platform, offering independent operation, significant savings in time, solvent and sample, and seamless transition of legacy assays to fast LC methods.

References

• United States Pharmacopeial Convention USP40 NF35 S1 Acetaminophen method The United States Pharmacopeial Convention 2017
• Franz H Fabel S A universal tool for method transfer from HPLC to UHPLC Technical note 75 Thermo Fisher Scientific 2016