Determination of methanesulfonic acid in busulfan by ion chromatography

Importance of methanesulfonic acid determination in busulfan therapy

Busulfan is a bifunctional alkylating agent widely used in conditioning regimens for hematopoietic stem cell transplantation. In aqueous environments it hydrolyzes to methanesulfonic acid (MSA) and tetrahydrofuran, making MSA both an indicator of drug instability and a potential toxic impurity. Monitoring MSA levels is therefore critical for ensuring product quality, patient safety, and compliance with pharmacopeial standards.

Objectives and Study Overview

The study aimed to evaluate the proposed United States Pharmacopeia (USP) Busulfan monograph limit test for MSA and to assess a modified protocol. Key goals included:

• Verifying chromatographic separation, system suitability, and performance of the USP method.
• Investigating sample preparation and autosampler temperature modifications to improve stability.
• Comparing analytical figures of merit, retention behavior, and impurity quantitation between methods.

Methodology and Instrumentation

MSA and busulfan were analyzed by ion chromatography with suppressed conductivity detection. Key elements included:

• Thermo Scientific Dionex ICS-6000 HPIC system with KOH eluent generator and ADRS 600 suppressor.
• Dionex IonPac AG11-HC guard column and AS11-HC analytical column (2×50 mm and 2×250 mm).
• Autosampler with temperature control (set to 25 °C for USP method; 8 °C for modified method).
• Sample preparation: solid-phase extraction on C18 cartridges; stock solutions in acetonitrile; working solutions in deionized water or cold 30 % acetonitrile/water.

Main Results and Discussion

The USP method yielded a well-resolved MSA peak at ~9.44 min with tailing factor <1.2 and RSD <3 %. Linearity was excellent (r2 >0.9999), and LOD/LOQ values were 1.25/4.16 µg/L. The modified protocol produced comparable separation, with LOD/LOQ of 3.45/11.5 µg/L. Stability tests showed that busulfan degradation to MSA was slowest in cold 30 % acetonitrile at 2–8 °C. Robustness studies confirmed method tolerance to ±10 % changes in flow rate, eluent concentration, and column temperature on two column lots. Analysis of three commercial samples (European, British, and analytical standards) demonstrated that one batch exceeded the 0.15 % MSA limit under USP conditions, whereas the modified method extended the analysis window up to 30 h with reliable quantitation. Recovery experiments in cold 30 % acetonitrile yielded 90–110 % accuracy for spiked levels.

Benefits and Practical Applications

The validated IC procedure provides a robust, sensitive, and compliance-ready approach for monitoring MSA in busulfan drug substance. The modified sample protocol enhances sample stability, allowing flexible scheduling without compromising accuracy.

Future Trends and Opportunities

Potential developments include integration with mass spectrometric detection for enhanced specificity, miniaturized and high-throughput IC platforms for real-time stability monitoring, and adoption of greener eluent systems. Automation of sample preparation and data handling will further streamline quality control workflows.

Conclusion

The study confirms that both the USP monograph method and the proposed modifications deliver reliable MSA quantitation in busulfan. The modified protocol offers an extended time window and maintains compliance with pharmacopeial requirements, supporting rigorous stability and impurity profiling.

Reference

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