Determination of methylisothiazolinone and methylchloroisothiazolinone in cosmetic products by ultra high performance liquid chromatography with tandem mass spectrometry

Isothiazolinone biocides are broad‐spectrum preservatives that are widely used in cosmetics, household, and industrial products. An increase in the number of cases of allergic contact dermatitis to isothiazolinone preservatives, namely, methylisothiazolinone and methylchloroisothiazolinone, have been recently noticed. The Food and Drug Administration relies on analytical methods to quantify levels of use of cosmetic ingredients and support enforcement action against products that are not in compliance with the law. In this study, an efficient ultra high performance liquid chromatography with tandem mass spectrometry method was developed and validated for the determination of methylisothiazolinone and methylchloroisothiazolinone in selected cosmetic products. The lower limit of quantitation was determined to be 0.1 μg/g for both preservatives. A survey of 24 cosmetic products was conducted and found concentrations of methylisothiazolinone and methylchloroisothiazolinone ranging from not quantified, or below the lower limit of quantitation, to 89.64 μg/g and not quantified to 10.31 μg/g, respectively.