Determination of Fatty Acid Composition in Polysorbate 80 using HPLC with Charged Aerosol Detection

Significance of the topic

Polysorbate 80 (Tween 80) is a widely used non-ionic surfactant in pharmaceuticals, foods and cosmetics. Accurate determination of its fatty acid composition is essential for raw material quality control, ensuring product safety, regulatory compliance and batch-to-batch consistency. Traditional GC-based assays require derivatization and lengthy sample handling; liquid chromatography with Charged Aerosol Detection (CAD) offers a robust alternative for non-chromophoric, semi-volatile analytes such as free fatty acids released from polysorbate 80.

Objectives and study overview

This application note describes development and validation of an HPLC-CAD method for quantifying fatty acids released from polysorbate 80 raw materials. Key aims were to achieve baseline separation of major fatty acids, optimize CAD parameters for sensitivity and linearity, establish limits of quantification and repeatability, and demonstrate applicability to multiple commercial batches while meeting USP compositional criteria.

Used instrumentation

• Arc HPLC System with column heater/cooler and active pre-heater
• Waters Charged Aerosol Detector (CAD), controlled via Empower 3.6.0
• XBridge BEH C18 Column, 4.6 x 100 mm, 3.5 µm
• LCMS maximum recovery vials, GHP syringe filters for final sample filtration

Methodology

The method combines saponification to release free fatty acids, liquid–liquid extraction and reversed-phase HPLC with CAD detection. Key elements:

• Sample preparation: Polysorbate 80 at 1.5 mg/mL in 90:10 of 1 M KOH/methanol, incubated 6 h at 40 °C; neutralized with formic acid; extracted with MTBE; organic layer dried under nitrogen and reconstituted in 25:75 water:acetonitrile (v/v); final samples filtered prior to injection.
• Chromatography: XBridge BEH C18, column temperature 60 °C, sample tray 10 °C, injection volume 35 µL, flow 1.5 mL/min. Mobile phase A = 0.05% formic acid in water; B = 0.05% formic acid in acetonitrile. Wash solvents and seal/purge washes implemented per system recommendations.
• CAD operating parameters (optimized): evaporator temperature 25 °C; filter time constant 1.4 s; sampling rate 10 pts/s; power function value (PFV) 1.00; ion trap voltage 20 V. Data acquisition and processing in Empower 3.6.0 using linear fit with 1/x weighting for calibration.

Results and discussion

• Chromatographic separation: The reversed-phase method achieved baseline separation of the principal fatty acids (including myristic, palmitoleic, palmitic, oleic, stearic and petroselinic acids) despite their lack of strong chromophores.
• CAD optimization: Evaporator temperature critically affected signal for semi-volatile fatty acids; best signal-to-noise (S/N) across analytes was at 25 °C. Filter time constant optimization showed 1.4 s delivered maximal S/N. PFV of 1.00 produced the best overall linearity (R2 ≥ 0.99 for most acids) across the tested range.
• Linearity and sensitivity: Calibration was linear over 0.05–25 µg/mL using 1/x weighting. Limits of quantification (LOQ) determined by S/N ≥ 10 were 0.9–3.5 ng on-column, demonstrating high sensitivity for low-level fatty acids.
• Precision and system suitability: Ten replicate injections of a 10 µg/mL standard yielded peak area %RSD ≤ 0.48% and retention time %RSD ≤ 0.02%, indicating excellent repeatability.
• Sample analysis and identity confirmation: Multiple commercial polysorbate 80 batches were analyzed after saponification. An additional peak eluting after oleic acid was observed and confirmed as petroselinic acid by spiking. Calculated compositions (area percent relative to total fatty acid peaks) showed oleic acid in the range 68.3–82.4%, meeting USP requirement of not less than 58%.

Benefits and practical applications

• The HPLC-CAD approach eliminates the need for complex GC derivatization (e.g., BF3-methanol reflux), reducing sample preparation time and potential artefacts.
• CAD provides a near-universal response for non-volatile species and supports gradient elution, improving workflow flexibility compared with RI or ELSD detectors.
• Optimizable detector parameters (PFV, evaporator temperature, filter time constant) allow tuning of dynamic range and sensitivity across heterogeneous excipient matrices.
• Integration with Empower software provides compliance-ready data handling, streamlined reporting and reduced validation burden for QC labs.

Future trends and applications

• Broader adoption of CAD-coupled LC methods for complex, non-chromophoric excipients and lipid-based formulations as labs seek to reduce derivatization steps and accelerate release testing.
• Further refinement of digital signal processing (PFV and related algorithms) to extend linear dynamic range and quantitation accuracy for trace-level components in complex matrices.
• Combination with high-resolution mass spectrometry for structural confirmation of minor or unexpected fatty acids while using CAD for routine quantification to balance throughput and information content.
• Standardization of HPLC-CAD workflows and suitability criteria for official monographs and pharmacopeial methods as CAD gains acceptance in regulated environments.

Conclusion

A robust HPLC-CAD method was developed and demonstrated for determining fatty acid composition in polysorbate 80. The method delivered sensitive LOQs (0.9–3.5 ng on-column), excellent repeatability (peak area RSD ≤ 0.48%), and reliable linearity across 0.05–25 µg/mL when processed with PFV = 1.00 and 1/x weighting. The workflow simplifies sample preparation relative to GC-based approaches and integrates with Empower software for compliance-ready QC implementation, supporting efficient raw material testing in pharmaceutical and related industries.

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