Studies on the stability of preservatives under subcritical water conditions.

The goal of this work was to further validate the subcritical water chromatography (SBWC) methods for separation and analysis of preservatives through the evaluation of analyte stability in subcritical water. In this study, the degradation of preservatives was investigated at temperatures of 100-200°C using two different approaches. First, the peak areas obtained by SBWC at high temperatures were compared with those achieved using the traditional high-performance liquid chromatography (HPLC) at 25°C. In the second approach, several preservatives and water were loaded into a vessel and heated at high temperatures for 30 or 60 min. The heated mixtures were then analysed by GC/MS to determine the stability of preservatives. The t- and F-test on the results of the first approach reveal that the peak areas achieved by HPLC and SBWC are not significantly different at the 95% confidence level, meaning that the preservatives studied are stable during the high-temperature SBWC runs. Although the results of the second approach show approximately 10% degradation of preservatives into mainly p-hydroxybenzoic acid and phenol at 200°C, the preservatives studied are stable at 100 and 150°C. This is in good agreement with the validation results obtained by the first approach. The findings of this work confirm that SBWC methods at temperatures up to 150°C are reliable for separation and analysis of preservatives in cosmetic and other samples.