Assay of tromethamine in pharmaceutical formulations

Significance of the Topic

Tromethamine is widely used in pharmaceutical and cosmetic formulations as a buffering and alkalizing agent. Precise quantification of tromethamine is critical for product quality control, regulatory compliance, and ensuring safety. Traditional titrimetric and derivatization methods lack specificity and increase labor. Ion chromatography (IC) with suppressed conductivity detection offers simultaneous analysis of common cations and high selectivity for tromethamine without derivatization.

Objectives and Study Overview

The goal of this work was to develop and validate an automated IC method for determining tromethamine in pharmaceutical formulations. The method employs a reagent-free IC system with electrolytically generated methanesulfonic acid (MSA) eluent, a Dionex IonPac CS20 cation-exchange column, and a CDRS suppressor to achieve high specificity and robustness.

Methodology and Instrumentation

The method uses isocratic elution with 2 mM MSA at 0.3 mL/min, column temperature of 40 °C, and a 2 × 250 mm IonPac CS20 analytical column with a 2 × 50 mm CG20 guard. A Dionex EGC 500 MSA cartridge generates eluent online, and a CDRS 600 suppressor provides continuous regeneration. Detection is by suppressed conductivity at 3 mA. Sample injection volume is 2.5 µL on a reagent-free IC system.

Used Instrumentation

• Dionex ICS-5000+ reagent-free IC system with DP dual pump and DC detector compartment
• AS-AP autosampler with cooling tray
• Dionex EGC 500 MSA eluent generator cartridge
• Dionex CR-CTC 500 cation trap column
• Dionex CDRS 600 suppressor (2 mm)
• IonPac CS20 analytical and CG20 guard columns

Main Results and Discussion

Separation of tromethamine from sodium and ammonium was achieved with resolutions ≥1.67. Method sensitivity yielded an LOD of 0.05 ppm and LOQ of 0.15 ppm. Linearity over 1-50 ppm produced an R² of 1. Precision studies at 2, 5, and 10 ppm showed retention time RSD ≤0.83% and area RSD ≤0.85%. Accuracy by spiking a diluted vaccine excipient matrix returned recoveries between 95% and 112%. Robustness tests revealed column temperature as the most critical parameter, with the chosen 40 °C balancing resolution of sodium, tromethamine, and ammonium.

Benefits and Practical Applications

The developed IC method provides:

• Automated, high-throughput quantification without derivatization
• Simultaneous determination of common cations and tromethamine
• Improved specificity compared to titrimetric assays
• Robust performance under small variations in flow, eluent concentration, and temperature

Future Trends and Opportunities

Advances in reagent-free IC and suppressor technologies may further reduce maintenance and improve sensitivity. The method could be extended to related amines, impurity profiling, and combination drug products. Integration with mass spectrometric detection could enhance selectivity for complex matrices.

Conclusion

An automated RFIC method using a Dionex IonPac CS20 column and suppressed conductivity detection was developed and validated for tromethamine determination. The assay meets USP <1225> criteria for accuracy, precision, linearity, and robustness, providing an efficient alternative to traditional titrimetric methods.

Reference

1. Tromethamine. USP43-NF38; 2. Constantinos CA, Koupparis MA. Analyst 1988;113:755; 3. Gumbhir K, Mason WD. J Chromatogr 1992;583:99; 4. Blanke SR, Blanke RV. J Anal Toxicol 1984;8:231; 5. Guo Y, Huang A. J Pharm Biomed Anal 2003;31(6):1191; 6. Bubois P et al. J Pharm Belg 1981;36:203; 7. Hulshoff A, Kostenbauder HB. J Chromatogr 1978;145:155; 8. Vincent G et al. J Chromatogr 1984;295:248; 9. Fritz JS et al. Anal Chem 1980;52:1519; 10. Hall RE et al. J Chromatogr A 1995;718(2):305; 11. USP <1225> Validation of Compendial Methods; 12. USP <621> Chromatography; 13. Johns Hopkins Institute of Vaccine Safety excipient list.