Procedure for evaluating the UV protection afforded by sun screen hair care products consists of plunging UV irradiated lock of hair in base solution

摘要

Applying sun screen hair treatment product to lock of hair, exposing to ultraviolet rays to provoke oxidation of the disulphide bridges in the cystine residues of the keratin in the hair making disulphide monoxide and disulphide dioxide, and then plunging the whole lock of hair in a base solution to produce a nucleophilic attack by OH ions on the disulphide monoxide and disulphide dioxide groups to produce thiolate ions which are then measured. Applying sun screen hair treatment product to lock of hair, exposing to ultraviolet rays to provoke oxidation of the disulphide bridges in the cystine residues of the keratin in the hair making disulphide monoxide and disulphide dioxide, and then plunging the whole lock of hair in a base solution to produce a nucleophilic attack by OH ions on the disulphide monoxide and disulphide dioxide groups to produce thiolate ions. The base solution is then recovered, and the quantity of sulphide ions dissolved in it is measured. The thiolate ions are measured by a potentiometric method at zero current using an electrode with a specific thiolate ion membrane, preferably with a silver sulphide crystal combined with a reference electrode.