The reaction of o-phthaldialdehyde with alkyl thiols and amino acids is well known. This method has been used to determine the concentration of taurine4and pico mole levels of amino acids5by liquid chromatography of the substituted isoindole formed. However, alkyl thiols are volatile and have noticeable odors. It was not known if this reaction works with arylthiols. Several aromatic thiols were investigated and triphenylmethanethiol which is a solid was found to react to give a fluorescent product which is most likely a substituted indole. The indole formed was studied with respect to stability as a function of time ans simplex optimization was used to study the factors involved in the derivatization reaction.