Preservatives based on methylisothiazolones in cosmetic products--theory and analysis

Abstract

Methyl isothiazolone formulations (Kathon CG) promoted as preservatives in the cosmetic field were investigated for their organic components by capillary gas chromatography/mass spectrometry. 2-methyl-3(2H)-isothiazolone and 5-chloro-2-methyl-3(2H)-isothiazolone were identified as effective major components and 4,5-dichloro-2-methyl-3(2H)-isothiazolone, 3-chloro-N-methyl-propionamide and dichloro-N-methyl-acetamide as minor components. Various methods like thin-layer chromatography with chemical and UV-detection, high-performance thin-layer chromatography using direct optical measurement, capillary gas chromatography with nitrogen selective thermionic detector, high-performance liquid chromatography with UV- resp. diode-array-UV-detector and UV-spectrometry were applied for detection and identification of the compounds. For quantitative determination it was necessary to obtain the corresponding purified isothiazolones as reference compounds. Commercial formulations were fractionated by reversed phase flash chromatography. Then the exact composition of the fractions obtained was determined by an absolute method, based on chemical reaction on a semi-micro scale. These solutions were used as reference for calibration. For quantitative determination of 2-methyl-3(2H)-isothiazolones reversed phase HPLC has proved to possess good reliability using the internal standard method (2-acetyl-5-chlorothiophen). Response factors and the relative calibration curves for this method were ascertained. A special technique based on extractive separation and purification by flash chromatography was developed for the isolation of 2-methyl-3(2H)-isothiazolone and 5-chloro-2-methyl-3(2H)-isothiazolone from cosmetic products. The average recovery rates and detection limits are given. The method was tested on several different commercial cosmetics. The samples contained between 5.5 and 39.4 mg/kg of methylisothiazolones.