Analysis of free fatty acids in soap samples by means of gas chromatography-mass spectrometry

In this work a new, accurate and reliable method, which has been applied to determine the quantitative and qualitative composition of free fatty acids in samples of laundry and toilet soap, is described. Silylation as a derivatization method for analysis of free fatty acids in soap samples by gas chromatography-mass spectrometry, using ammonium sulfate as a catalyst, a low-cost silylating agent hexamethyldisilazane (HMDS) and chloroform as a solvent, was evaluated. Gas chromatography-mass spectrometry analysis was carried out using a DB-5 capillary column. The method was validated for linearity, precision and limits of detection and quantification. It was found that the validated method had an acceptable linearity with the determination coefficient >0.999 within the concentration range 0.005-2 mg/ml. The limits of detection and quantification were obtained from the regressive analysis and were 2.5 and 8 mu g/ml, respectively. The validated method was applied for analysis of four samples of different quality soaps. The determined amount of free fatty acids in the soaps was ranging between 1.24 and 5.09%. This method can be applied to the analysis of the composition of free fatty acids in different soap samples.