UV-Vis Spectroscopy for White Mineral Oil Analysis per ASTM D2269-10

Importance of the Topic

White mineral oils play a critical role as excipients and starting materials in pharmaceutical formulations. Regulatory standards demand trace-level purity testing to protect patient safety and product efficacy. Ultraviolet (UV) spectrophotometry, following ASTM D2269-10 and USP-NF guidelines, provides a rapid, reliable measure of naphthalene contamination in mineral oils, making it essential for routine quality control in pharmaceutical manufacturing.

Objectives and Study Overview

The primary goal was to evaluate the performance of the Agilent Cary 3500 Multicell UV-Vis spectrophotometer and Agilent Cary UV Workstation software for ASTM D2269-10–compliant purity testing of white mineral oils. Three commercially available mineral oil samples were analyzed, and their naphthalene impurity levels were compared to the USP-NF acceptance limit. The study also demonstrated software-driven workflow enhancements for data acquisition, analysis, and reporting.

Methodology and Instrumentation

Sample and Standard Preparation:

• Standard solution: 7.0 mg/L naphthalene in isooctane.
• Sample extraction: 25 mL mineral oil mixed with hexane and dimethyl sulfoxide (DMSO), separated, and collected in quartz cuvettes.
• Solvent control: DMSO-hexane blank processed identically.

Instrumentation:

• Agilent Cary 3500 Multicell UV-Vis spectrophotometer with seven-cell capacity.
• Agilent Cary UV Workstation software for sequence setup, end-of-sequence analysis, and report generation.

Data Collection Parameters:

• Wavelength range: 260–350 nm
• Data interval: 1 nm
• Spectral bandwidth: 2 nm
• Signal averaging time: 0.1 s

Main Results and Discussion

Acceptance Limit Calculation:
The USP-NF specifies that sample absorbance must not exceed one-third of the standard solution absorbance at 275 nm. The measured standard absorbance of 0.2991 Abs yielded an impurity threshold of 0.0997 Abs.

Quantitative Analysis:
Using the Cary UV Workstation’s end-of-sequence analysis, each sample’s maximum absorbance in the 260–350 nm range was compared to 0.0997 Abs. Two out of three oils fell below the threshold and passed; one oil exceeded the limit and failed, indicating significant naphthalene contamination.

Precision Assessment:

• Repeatability (n=20): Maximum within-run variation was 1.28×10⁻³ Abs, well below the 0.014 Abs criterion.
• Reproducibility: Inter-operator standard deviation differences did not exceed 1.16×10⁻³ Abs, under the 0.044 Abs limit.

Benefits and Practical Applications

The multicell design enabled simultaneous measurement of up to seven samples plus reference, boosting throughput and minimizing environmental variability. The Cary UV Workstation software streamlined compliance by automating calculations, overlaying reference spectra, preserving audit trails, and generating consolidated PDF reports with user-defined content.

Future Trends and Potential Applications

Advances in UV-Vis spectroscopy workflows may include:

• Integration with laboratory information management systems (LIMS) for real-time data transfer.
• AI-driven spectral interpretation and anomaly detection.
• Miniaturized multicell designs for field or at-line analysis.
• Expansion of the method to detect other trace aromatic impurities.

Conclusion

The Agilent Cary 3500 Multicell UV-Vis spectrophotometer, paired with Cary UV Workstation software, meets ASTM D2269-10 precision requirements and USP-NF acceptance criteria for naphthalene purity testing in white mineral oils. Its high throughput, automated analysis, and robust reporting make it a reliable solution for pharmaceutical quality control.

Reference

1. Pirow R, Blume A, Hellwig N, et al. Mineral Oil in Food, Cosmetic Products, and in Products Regulated by Other Legislations. Crit Rev Toxicol. 2019;49(9).
2. Weber S, Schrag K, Mildau G, et al. Analytical Methods for Determination of MOSH and MOAH—A Short Review. Anal Chem Insights. 2018;13.
3. United States Pharmacopeial Convention. USP-NF Mineral Oil Monograph. 2024.
4. ASTM International. ASTM D2269-10 Standard Test Method for Evaluation of White Mineral Oils by Ultraviolet Absorption. ASTM Volume 05.01. 2020.