Study of solvent effect on the stability of isothiocyanate iberin, a breakdown product of glucoiberin

Iberin (IBR) is an isothiocyanate (ITC) with chemopreventive properties on different types of cancer. The need of quantifying IBR either in natural products or in food supplements makes the availability of suitable and stable analytical standards necessary. The choice of proper solvents for ITCs storage and experiment setup is a critical point due to ITCs reactivity. As IBR reference standard is sometimes supplied in ethanol, methanol is also frequently utilised as a solvent in ITCs analysis. A study on IBR stability in the most common solvents used in liquid chromatography and at different pH is presented. A fast UHPLC-PDA-ESI/MS analysis was used to separate IBR from degradation products, to monitor IBR stability at three temperatures and at different pH. The fastest degradation was observed in methanol/water mixture. IBR degraded always faster in methanol than in ethanol. At 20 degrees C, the degradation in ethanol and in water was comparable. At 30 degrees C and 40 degrees C the degradation in water was faster than either in ethanol or methanol. Ethyl thiocarbamate, methyl thiocarbamate and disubstituted thiourea degradation products, in ethanol, methanol and water respectively, were tentatively assigned. IBR was stable in acetonitrile and at acidic pH but it was unstable at alkaline pH.