Rapid Analysis of Fatty Acid Composition in Polysorbate 80 by Gas Chromatography with On-line Pyrolytic Methylation Technique

A novel method of on-line pyrolytic methylation–gas chromatography was developed for the rapid analysis of fatty acid composition in Polysorbate 80 without any tedious pre-treatment steps. Fatty acids in Polysorbate 80 were converted into their corresponding fatty acid methyl esters in the presence of trimethylsulfonium hydroxide with a vertical microfurnace pyrolyzer at 300 °C. The premixing procedure of sample and organic alkali reagent was necessary before the on-line pyrolytic methylation to improve the repeatability. The relative standard deviations for peak areas of fatty acids in Polysorbate 80 were over the range of 0.3–9.1% ( n  = 5). Six Polysorbate 80 samples, consisting of three samples of pharmaceutical grade and three samples of non-pharmaceutical grade, were analyzed to evaluate the feasibility of the proposed method. The relative percentages (%) of fatty acids for samples of pharmaceutical grade meet the Chinese Pharmacopoeia requirements with the amount of oleic acid varying from 78.4 to 89.3%. On the other hand, the relative percentages (%) for palmitic acid and stearic acid in samples of non-pharmaceutical grade were out of the specification limits, with the amount of oleic acid varying from 62.0 to 63.5%. The quantitative results determined by on-line pyrolytic methylation were in agreement with those obtained by off-line methylation. The result proved that gas chromatography with on-line pyrolytic methylation technique is of great value for rapid screening analysis of Polysorbate 80 samples in bulks.