Chromatographic Assay of Tolbutamide Using the ACQUITY UPC2 System

Significance of Topic

The increasing demand for rapid, cost-effective, and environmentally friendly analytical methods has led to the adoption of supercritical fluid chromatography (SFC) as a green alternative to traditional normal phase HPLC. Converting compendial HPLC assays to SFC reduces solvent consumption, lowers operational costs, and aligns with sustainability goals without compromising data quality.

Objectives and Study Overview

The primary goal was to translate the USP-defined normal phase HPLC assay for tolbutamide into an SFC-based UltraPerformance Convergence Chromatography (UPC2) method using the Waters ACQUITY UPC2 System. The study aimed to achieve comparable or superior analytical performance, significantly shorten run times, and minimize solvent usage.

Methodology and Instrumentation

• Sample preparation: Tolbutamide with tolazamide as internal standard, following USP procedures.
• Conventional HPLC method: Isocratic normal phase using silica column (4.0×300 mm), hexane/water-saturated hexane/THF/alcohol/acetic acid, 20 min runtime.
• UPC2 method: ACQUITY UPC2 BEH column (3.0×100 mm, 1.7 μm), 50 °C.
• Mobile phase: 95% CO₂ / 5% methanol/isopropanol (1:1) with 0.2% TFA.
• Flow rate and pressure: 2.5 mL/min at 120 bar.
• Detection: UV/PDA at 254 nm.

Used Instrumentation

• ACQUITY UPC2 System with BEH column (3.0×100 mm, 1.7 μm)
• Refrigerated autosampler and column heater (50 °C)
• UV/PDA detector (254 nm)
• CO₂ delivery module and back-pressure regulator

Main Results and Discussion

• Run time: Reduced from ~20 min (HPLC) to 2.0 min (UPC2).
• Resolution: Maintained high separation (R ≈ 15) between tolbutamide and tolazamide.
• Precision: Retention time RSD ≤ 1.2% for tolbutamide and ≤ 0.9% for tolazamide (n=6); area RSD < 0.90%.
• Tailing factor: Improved from 1.65 (HPLC) to 1.2 (UPC2).
• Sensitivity: Additional minor impurities resolved with higher efficiency.
• Solvent reduction: From ~29 mL hexane + >1 mL THF/ethanol per run to 0.25 mL methanol + 0.25 mL IPA.
• Cost savings: Reagent cost per run dropped from ~$1.40 to ~$0.01.

Benefits and Practical Applications

• Substantial decrease in organic solvent usage, supporting green chemistry initiatives.
• Enhanced laboratory throughput due to faster analysis times.
• Lower operational costs and waste disposal expenses.
• Equivalent or improved analytical performance versus compendial HPLC.
• Applicability to other normal phase assays seeking greener alternatives.

Future Trends and Possibilities

• Broader application of SFC/UPC2 to diverse pharmaceutical assays.
• Integration with mass spectrometry for enhanced specificity.
• Automation and high-throughput screening using supercritical fluids.
• Development of new stationary phases designed for UPC2.
• Regulatory acceptance of SFC methods in pharmacopeial monographs.

Conclusion

The conversion of the USP normal phase HPLC assay for tolbutamide to an SFC-based UPC2 method demonstrated significant advantages in speed, solvent consumption, cost efficiency, and chromatographic performance. This work underscores the potential of supercritical fluid chromatography to modernize pharmaceutical analysis while supporting sustainability and productivity goals.

Reference

• Waters Corporation. Chromatographic Assay of Tolbutamide Using the ACQUITY UPC2 System. Application Note. 2012.