The composition analysis of free and bonded fatty acids in Polysorbate 80 by on-line two-step pyrolytic methylation-gas chromatography

An on-line two-step pyrolytic methylation technique combined with gas chromatography was developed for rapid analysis of free and bonded fatty acids in Polysorbate 80 respectively. Free fatty acids in Polysorbate 80 were transformed to their corresponding fatty acid methyl esters in the presence of tetramethylammonium acetate (TMAAc) in the first step with a vertical microfurnace pyrolyzer at 300 °C. After the analysis of free fatty acids, bonded fatty acids were then transformed into methyl esters in the presence of tetramethylammonium hydroxide (TMAH) at 300 °C. The effects of pyrolytic methylation temperature, TMAAc concentration and ratio to Polysorbate 80 were evaluated. The range of linearity, reproducibility, the detection limits (LODs), and the quantitation limits (LOQs) were also investigated using linoleic (C18:2), oleic (C18:1), stearic (C18:0) acids. The recoveries ranged from 92.2 to 105.0%. The RSDs of intra-day and inter-day precision were in the range of 2.89–5.9% (n = 6) and 4.4–7.2% (n = 3) respectively. Compositions of free and bonded fatty acids in five Polysorbate 80 samples were analyzed respectively to evaluate the feasibility of the proposed method. The results prove that the proposed method is simple, solvent saving and environmentally friendly since it avoids off-line derivatization and solvent extraction, and has a potential application in the high quality control of Polysorbate 80.