Method Verification of the United States Pharmacopeia Monograph with the Agilent Cary 60 UV-Vis

Importance of the Topic

Pharmaceutical quality control relies on accurate measurements of trace impurities to ensure patient safety and regulatory compliance.
Iron content in excipients such as magnesium sulfate must be tightly controlled according to USP monographs.
UV-Vis spectrophotometry offers a cost-effective and robust technique for impurity analysis within pharmaceutical laboratories.

Objectives and Study Overview

This application note demonstrates verification of the USP Magnesium Sulfate monograph procedures using the Agilent Cary 60 UV-Vis spectrophotometer.
Key aims include verifying accuracy, precision, specificity, and quantitation limit for iron determination in magnesium sulfate.
The validated method was applied to two real samples to assess compliance with the USP limit of 0.5 μg/g iron.

Methodology

Sample and standard preparation

• Dilute HCl used to prepare blank, standards (0.04, 0.1, 0.2 mg/L iron), and sample solutions.
• Magnesium sulfate samples dissolved in dilution matrix.
• Color reagent and reductant solutions added to each solution.

Calibration and measurement

• Calibration curve established from three matrix-matched standards at 594 nm.
• Blank subtraction, signal averaging, and wavelength settings per USP <857>.
• Measurements automated using an 18-cell multicell changer.

Used Instrumentation

• Agilent Cary 60 UV-Vis spectrophotometer with xenon lamp light source.
• 18-cell multicell changer for automated loading.
• Agilent Cary WinUV software Concentration and Scan applications.

Main Results and Discussion

• Accuracy assessed by recovery of spiked samples yielded 94.6–102.0%, within USP limits of 80–120%.
• Precision (repeatability) tested on six replicates at assay concentration showed RSD of 1.8%, below the 15–20% threshold.
• Specificity confirmed by scan comparison of blank and iron–reagent complex with no interfering peaks around 594 nm.
• Quantitation limit estimated at 0.00231 mg/L based on blank replicates, meeting sensitivity requirements.
• Iron content in two magnesium sulfate samples measured at 0.31 and 0.25 μg/g, under the USP limit of 0.5 μg/g.

Benefits and Practical Applications

• Automated measurement reduces manual handling and increases throughput.
• Long-life xenon lamp minimizes maintenance costs and downtime.
• Method meets USP compendial verification criteria for routine QA/QC workflows in pharmaceutical laboratories.

Future Trends and Potential Applications

• Integration with electronic record systems for full regulatory compliance (21 CFR Part 11, EU Annex 11).
• Expansion of UV-Vis methods for multi-element impurity profiling.
• Adoption of greener laboratory practices through energy-efficient instrumentation.

Conclusion

The Agilent Cary 60 UV-Vis spectrophotometer successfully verified USP conditions for iron determination in magnesium sulfate, demonstrating robust accuracy, precision, and specificity. The instrument’s automation capabilities and long-term reliability make it suitable for routine pharmaceutical QC and R&D settings.

References

1. United States Pharmacopeia. General Chapter <1226> Verification of Compendial Procedures. USP-NF. Rockville, MD: United States Pharmacopeia, 2024. DOI: https://doi.org/10.31003/USPNF_M870_03_01
2. United States Pharmacopeia. General Chapter <857> Ultraviolet-Visible Spectroscopy. USP-NF. Rockville, MD: United States Pharmacopeia, 2022. DOI: https://doi.org/10.31003/USPNF_M3209_03_01
3. Agilent Technologies. Spectroscopy Solutions for Pharmaceuticals: Confidence in Compliance to USP <857> Using the Agilent Cary 60 UV-Vis Spectrophotometer. White paper, publication number 5991-7269EN, 2016.
4. United States Pharmacopeia. USP Monographs, Magnesium Sulfate. USP-NF. Rockville, MD: United States Pharmacopeia, 2024. DOI: https://doi.usp.org/USPNF/USPNF_M47040_06_01
5. Agilent Technologies. Improved Lab Efficiency with the Agilent 18-Cell Changer Accessory. Technical overview, publication number 5994-7250EN, 2024.