Global round robin test of thiopental EP method performance on identical HPLC systems

Importance of the Topic

The ability to achieve consistent chromatographic results across multiple HPLC instruments is crucial in pharmaceutical quality control, method transfer between research and manufacturing labs, and routine batch testing. High system-to-system reproducibility minimizes retesting, streamlines workflows, and ensures regulatory compliance when applying compendial methods such as the European Pharmacopoeia (EP) assay for thiopental and its impurities.

Objectives and Overview of the Study

This global round-robin study assessed the reproducibility of the EP thiopental method on Thermo Scientific Vanquish Core HPLC systems. Key goals:

• Quantify intra- and inter-laboratory precision for retention times, peak areas, and relative quantification.
• Evaluate system-to-system variability under controlled and real-world conditions.
• Investigate the impact of different operators, column lots, eluent grades, and sample preparations.

Methodology and Instrumentation

Eight laboratories in four countries deployed identical Vanquish Core systems to analyze thiopental sodium and impurities A–D, following the EP monograph. All labs prepared mobile phase by acidifying water (1 g phosphoric acid in 1 L) and mixing with acetonitrile (35% v/v). The system suitability standard (1 mg/mL thiopental with impurities) was dissolved in mobile phase. Chromatography was performed isocratically on a Hypersil GOLD C18 column (150 × 4.6 mm, 5 µm) at 25 °C, flow rate 1 mL/min, UV detection at 225 nm. Data were acquired with Chromeleon CDS 7.3.

Instrumentation Used

• Vanquish Core Quaternary and Binary HPLC systems (Base VC-S01-A)
• Quaternary Pump C (VC-P20-A) or Binary Pump C (VC-P10-A)
• Split Sampler CT (VC-A12-A), Column Compartment C (VC-C10-A-03)
• Diode Array Detector CG (VC-D11-A) or Variable Wavelength Detector C (VC-D40-A)
• Hypersil GOLD C18 column (150 × 4.6 mm, 5 µm)
• Chromeleon Chromatography Data System v7.3

Main Results and Discussion

Controlled inter-system comparisons (three identical systems, sample, eluent, and column moved between instruments) yielded excellent precision: thiopental retention time RSD 0.4%, peak area RSDs ≤2.3% for four of five analytes. All systems met EP system suitability criteria (resolution ≥1.5).
In the global test (eight systems), all sites passed the system suitability test. Retention times for impurities A–D relative to thiopental matched EP expectations within column variability. Variations in retention were driven more by slight differences in eluent preparation than by system or column lot.
Peak area variability was dominated by sample inhomogeneity in the EP reference standard vials. Larger peaks (thiopental, impurities A, C) exhibited RSDs <0.3% when S/N >1 000. Smaller peaks (impurity B, D) with S/N <60 showed RSDs up to 4.4%. Pump type (binary vs. quaternary) had no measurable impact under isocratic conditions.

Benefits and Practical Applications

This study demonstrates that Vanquish Core systems deliver predictable, robust performance for routine EP assays when critical variables are controlled. Laboratories can confidently deploy multiple identical systems for QA/QC, reducing method revalidation efforts and ensuring consistent release testing in pharmaceutical production.

Future Trends and Applications

Advancements may include automated eluent and sample preparation modules to further reduce variability, integration of digital twins for predictive method transfer, and application of machine learning to optimize system suitability criteria. The approach can extend to other compendial assays, small-molecule impurities, and biosimilar analyses.

Conclusion

The global round-robin test confirms that Thermo Scientific Vanquish Core HPLC systems achieve exceptional system-to-system reproducibility for the EP thiopental method. Controlling sample and eluent preparation is essential to minimize variability in retention times and peak areas. The results support reliable method transfer and routine high-throughput quality control workflows.

Reference

1. European Pharmacopoeia 9.0, “Thiopental sodium and sodium carbonate,” 07/2012:0212.
2. European Directorate for the Quality of Medicines & HealthCare; European Pharmacopoeia (Ph. Eur.); Allée Kastner CS 30026, F-67081 Strasbourg, France.
3. MacMod Analytical Inc., “Comparison Guide to C18 Reversed Phase HPLC Columns,” 4th ed., June 2008.