Ion chromatography determination of nitrate and nitrite in metformin API and tablets

Importance of the Topic

This work addresses a critical safety concern in pharmaceutical manufacturing: the presence of nitrite and nitrate impurities in metformin hydrochloride. Nitrosamine formation pathways involving nitrite-containing reagents pose genotoxic risks. Reliable quantification of these anions supports regulatory compliance and patient safety by preventing potential carcinogen contamination.

Objectives and Study Overview

The primary goal is to develop and validate a robust ion chromatography method with suppressed conductivity detection for simultaneous determination of nitrite and nitrate in metformin API, finished tablets, and related excipients. Key performance parameters include sensitivity, specificity, linearity, precision, and recovery.

Methodology and Instrumentation

Sample preparation protocols differ by matrix but follow a common scheme of dilution, sonication, 0.2 µm filtration, and cleanup with OnGuard II RP cartridges to remove interferences. Freshly prepared eluent comprises a gradient of sodium hydroxide (5 mM to 50 mM) delivered over 40 min at 1 mL/min. Calibration standards cover 0.1–25 mg/L for linearity and down to 0.025 mg/L for limit of detection assessments.

Used Instrumentation

• Thermo Scientific Dionex ICS-6000 HPIC system including gradient pump, thermostat-controlled autosampler, suppressed conductivity detector
• IonPac AS19 analytical column (4 × 250 mm, 4 µm) with AG19 guard column
• Thermo Scientific Dionex ADRS 600 dynamically regenerated suppressor in recycle mode

Results and Discussion

• Retention times: nitrite at 13.27 min, nitrate at 16.78 min with baseline separation from common anions such as fluoride and phosphate.
• Calibration achieved R2 values of 0.999 for both analytes, with slope and offset within acceptable limits.
• Limits of detection and quantification were determined at 0.025 mg/L and 0.1 mg/L, respectively.
• Average recoveries across LOQ, 50 , 100 , and 150 levels ranged from 90 to 115 , demonstrating method accuracy.
• Sample analysis showed nitrite not detected in most API and tablet batches; nitrate levels ranged from 14.7 to 25.5 mg/kg. Excipients exhibited higher nitrite (up to 15.6 mg/kg) and nitrate (up to 135 mg/kg) content.

Practical Applications and Benefits

The validated IC method enables quality control laboratories to screen metformin raw materials, intermediates, and final dosage forms for nitrosating impurities in a single analytical run. It supports risk assessment for genotoxic impurities and helps maintain compliance with international guidelines.

Future Trends and Opportunities

Emerging developments include coupling ion chromatography with mass spectrometry for enhanced sensitivity and specificity, adoption of automated sample handling to increase throughput, and implementation of greener eluent systems to reduce reagent consumption and waste.

Conclusion

This study presents a validated, reliable ion chromatography method for sensitive and accurate quantification of nitrite and nitrate in metformin matrices. It offers robust performance suitable for routine pharmaceutical testing and impurity monitoring.

References

• FDA Updates and Press Announcements on NDMA in Metformin accessed July 7 2021
• AN73987 Determination of Nitrite in Pharmaceuticals accessed March 23 2021
• TN74093 Designing Ion Chromatography Methods for Determining Amines in Pharmaceuticals accessed May 19 2021