IC-MS for the determination of organic acids in pharmaceutical solutions

Significance of the topic

Highly polar, low molecular weight organic acids often appear as trace impurities in pharmaceutical starting materials, formulations, and cleaning solutions. Their hydrophilicity and low retention present challenges for conventional chromatographic techniques. Combining ion chromatography (IC) with mass spectrometric (MS) detection overcomes these limitations, offering enhanced selectivity and sensitivity for impurity monitoring.

Study aims and overview

This application demonstrates a streamlined IC–MS workflow for simultaneous identification and quantification of short‐chain aliphatic and unsaturated organic acids at single‐digit µg/L levels in complex pharmaceutical matrices. The method aligns with regulatory requirements for impurity profiling and cleaning validation.

Methodology and applied instrumentation

The separation was performed on a Thermo Scientific™ Dionex™ IonPac™ AS11-HC-4 µm column (2 × 250 mm) with a dynamically regenerated membrane suppressor and a KOH gradient (1 → 54 mM) at 40 °C. Suppressed conductivity detection was coupled with an ISQ™ EC single quadrupole mass spectrometer operated in negative electrospray ionization (ESI) mode. A make‐up solvent of 50/50 acetonitrile–water with 25 mg/L ammonium hydroxide (0.1 mL/min) was introduced post‐separator to enhance desolvation and ionization.

Used Instrumentation

• Dionex Integrion™ HPIC system with RFIC™ eluent generation
• Dionex ADRS™ 600 suppressor, Dionex AS-AP autosampler
• Dionex IonPac AG11-HC guard and AS11-HC-4 µm columns
• ISQ™ EC single quadrupole mass spectrometer, HESI-II interface
• Thermo Scientific™ EGC 500 KOH eluent cartridge
• Peak Scientific Genius NM32LA nitrogen generator

Main results and discussion

Second‐order calibration curves (1–500 µg/L) yielded correlation coefficients ≥0.9992 for all acids. Limits of detection (LODs) by MS ranged from 1.3 to 11.4 µg/L; suppressed conductivity LODs were 0.8–4.4 µg/L. MS in SIM mode enabled interference‐free quantification and confirmation, even when analytes co-eluted in conductivity traces. Repeatability tests at 0.005–0.1% relative levels in a 25 mg/L 2-butynoic acid matrix showed response deviations within ±20% down to single‐digit µg/L additions.

Benefits and practical applications

• High selectivity and sensitivity for trace organic acids
• Interference‐free quantification via MS confirmation
• Automated RFIC™ workflow reduces manual preparation and improves reproducibility
• Suitable for impurity profiling, stability studies, and cleaning validation in pharmaceutical environments

Future trends and possibilities

Advancements may include higher‐resolution MS detection for isobaric compound discrimination, integration with automated data analytics, and expansion to a broader range of polar impurities. Online monitoring of gradient and suppressor performance could further streamline compliance documentation.

Conclusion

The presented IC–MS method offers a robust, fully automated solution for simultaneous trace determination of multiple organic acids in pharmaceutical matrices. Its high sensitivity, selectivity, and reproducibility make it a valuable tool for QA/QC laboratories facing stringent regulatory demands.

Reference

1. Thermo Fisher Scientific, Inc. Pharmaceutical Applications Notebook: Controlled Drugs. 2012.
2. Weiss, J. Handbook of Ion Chromatography, 4th ed.; Wiley‐VCH: 2016.
3. Husain, S. et al. J. Chromatogr. A 1992, 600, 316–319.
4. Valto, P. et al. J. Sep. Sci. 2011, 34, 925–930.
5. Kim, B.-H.; Cho, H. S. J. Chromatogr. Sci. 2015, 53, 849–853.
6. Jurado-Sánchez, B.; Gallego, M. Talanta 2011, 84, 924–930.
7. Park, Y. J. et al. J. Agric. Food Chem. 1999, 47, 2322–2326.
8. Harrold, M. P. et al. J. Chromatogr. A 1993, 640, 436–471.
9. Jandik, P. et al. LC-GC 1991, 9, 634–642.
10. Hajós, P.; Nagy, L. J. Chromatogr. B 1998, 717, 27–38.
11. Ammann, A. A.; Rüttimann, T. B. J. Chromatogr. A 1995, 706, 259–269.
12. Brinkmann, T. et al. Vom Wasser 2000, 94, 41–50.
13. Trick, J. et al. Anal. Lett. 2016.
14. Huang, B. et al. AB-72363; 2017.
15. Wang, J.; Schnute, W. C. Rapid Commun. Mass Spectrom. 2009, 23, 3439–3447.
16. Corry, T. A. et al. J. Chromatogr. A 2019, 1604, 460–470.
17. ICH Q2(R1) Validation of Analytical Procedures: Text and Methodology; 2006.
18. ISO 8466-2:2001 Water quality – Calibration strategy for non-linear calibration functions; 2001.