Quantification of Methylisothiazolinone and Methylchloroisothiazolinone Preservatives by High-Performance Liquid Chromatography

Isothiazolinone preservatives (methylisothiazolinone (MIT) and methylchloroisothiazolinone (CMIT) are commonly used in cosmetics, industrial and household products. However, these isothiazolinone derivatives are known to cause allergic contact dermatitis. Hence, a sensitive, accurate, and reliable method for the detection of these compounds is thus warranted. The study aims to analyze concentrations of MIT and CMIT by high performance liquid chromatography. The analytical method used for quantification of MIT and CMIT in cosmetic products (leave-on-baby wet wipes) complies with the validation acceptance criteria (international standards ISO 5725, EU25 European Union for cosmetic regulations). MIT and CMIT were extracted and analyzed in leave-on baby wet-wipes collected from different stores in Riyadh city. Extraction was performed by ultrasonication of the samples, solid-phase extraction, and liquid-liquid extraction. Ten (10) µL of the sample was injected into the HPLC system and samples were analyzed with a mixture of acetic acid and methanol (80:20 v/v) in an isocratic mode. The flow rate was maintained at 1 mL/min. UV detection was performed at 274 nm. The results demonstrated recoveries between 90 and 106%, measurement uncertainty of C +/− 0.4% for methylisothiazolinone and C +/− 0.03% for methylchloroisothiazolinone, repeatability limit (r = 0.2%) and intermediate precision limit; R = 2% and R² of 0.9996.