Behavior of thymol blue analytical pH-indicator entrapped into sol–gel matrix

The preparation of transparent monolithic silica doping with thymol blue has been carried out by the acid catalyzed sol–gel reaction of tetraethylorthosilicate in the presence of thymol blue. The immobilized thymol blue pH-indicator shows similar behavior as its solution counterpart. The UV/VIS spectra indicate that the thymol blue retains its structure during the sol–gel reactions in terms of response to pH. Thymol blue can be regarded as uniformly distributed in the sol–gel matrix, and the use of SDS surfactant has positive effects on the immobilized thymol blue monolithic disk by homogenizing the polymerizing system. This research shows that thymol blue indicator can be used as solid pH sensor.