Detection of Low-Level Impurities in Salbutamol Using the Agilent 1260 Infinity II SFC System with a Variable Wavelength Detector

Importance of the Topic

The detection of trace level impurities in active pharmaceutical ingredients is critical to ensure drug safety and regulatory compliance. Salbutamol is a widely used bronchodilator, and its purity is governed by pharmacopeial limits for organic impurities. Rapid and reliable analytical methods support quality control and reduce time to release for pharmaceutical products.

Objectives and Study Overview

This study presents the development and validation of a supercritical fluid chromatography method combined with a variable wavelength detector for the sensitive and fast quantification of five low-level impurities in salbutamol sulfate. The method aims to achieve separation within 7 minutes, determine impurity levels at 0.2 to 0.4 percent, and demonstrate intraday repeatability and interday precision as part of a round robin evaluation.

Methodology and Instrumentation

The method employs a silica-based diethylamine column (100 × 3.0 mm, 1.7 μm) under supercritical CO2 conditions with methanol containing 0.1 percent ammonium hydroxide as modifier. A gradient program increases modifier from 3 to 35 percent over 6.5 minutes. Back pressure is set at 135 bar and column temperature at 55 °C. Injection volume is 2 μL with a feed solvent of methanol/water 90/10. Detection is performed at 220 nm.

• Sample preparation involves dissolving salbutamol sulfate and impurity standards in water and acetonitrile, followed by independent replicate solutions.
• Calibration was carried out at 4, 6, and 8 μg/mL for impurity D, yielding linear responses with R2 greater than 0.996.
• System suitability was evaluated by six injections of a standard solution test, confirming retention time RSD below 0.03 percent and peak area RSD below 2 percent for all impurities.

Used Instrumentation

• Agilent 1260 Infinity II SFC Control Module
• Agilent 1260 Infinity II SFC Binary Pump
• Agilent 1260 Infinity II SFC Multisampler
• Agilent 1290 Infinity II Variable Wavelength Detector with 10 mm high pressure flow cell
• Agilent OpenLab CDS ChemStation edition

Main Results and Discussion

The method resolved salbutamol and five related impurities within a 7-minute run. Peak retention times and areas exhibited excellent precision with intraday RSD values for impurity quantification at or below 1 percent. Interday precision RSD values ranged from 0.44 to 1.76 percent across impurity levels of 0.2, 0.3, and 0.4 percent. Calibration curves for impurity D demonstrated linearity with recovery at 98.9 percent, and sample measurements matched theoretical impurity levels with minimal variation.

Benefits and Practical Applications

This fast SFC method enhances throughput in quality control by reducing analysis time by a factor of seven compared to conventional HPLC. The robust performance at low flow rates and elevated temperatures provides reliable trace impurity monitoring. The technique is well suited for pharmaceutical laboratories requiring rapid release testing and routine impurity profiling.

Future Trends and Potential Applications

Supercritical fluid chromatography is poised to expand in pharmaceutical analysis with multi lab validation across different instrument vendors. Future developments may include coupling SFC with mass spectrometry for improved sensitivity, exploring chiral separations of enantiomeric impurities, and adopting greener mobile phases. High-throughput impurity screening workflows and automated data processing will further enhance productivity.

Conclusion

The Agilent 1260 Infinity II SFC system with a variable wavelength detector provides a rapid, precise, and sensitive solution for trace impurity quantification in salbutamol sulfate. The validated method meets pharmacopeial requirements, offers significant time savings, and demonstrates excellent repeatability and reproducibility, supporting its implementation in pharmaceutical quality control settings.

References

• Roy J Pharmaceutical Impurities A Mini Review AAPS PharmSciTech 2002 3 2 1–8 article 6
• ICH Harmonized Tripartite Guideline Impurities in New Drug Products Q3B R2
• Dispas A et al Interlaboratory Study of a Supercritical Fluid Chromatography Method for the Determination of Pharmaceutical Impurities Evaluation of Multi Systems Reproducibility J Pharm Biomed Anal 2021 203 114206
• Dispas A et al Quantitative Determination of Salbutamol Sulfate Impurities Using Achiral Supercritical Fluid Chromatography J Pharm Biomed Anal 2017 134 170–180
• Dispas A Marini R Desfontaine V First Inter Laboratory Study of Supercritical Fluid Chromatography Method for the Determination of Pharmaceutical Impurities J Pharm Biomed Anal 2018 161 414–424