Design and fabrication of optical sensor by immobilization of natural reagents on the sol-gel monolith for pH determination

Due to importance of pH measurement in different aqueous environments and its effects on living creatures [۱-۳]. Therefore, in this study, the aim is to present a new, simple, sensitive and inexpensive analytical method based on optical sensing for pH measurement. Two optical sensors, based on the natural pigments (purple cabbage and red beetroot) doped on the sol-gel substrate, were designed and used to measure pH in different aqueous environments. The spectral properties of the prepared sensors were studied using visible spectrophotometer at their maximum absorption wavelength (۵۳۰ nm for purple cabbage and ۴۸۰ nm for red beetroot). The effective variables which affect on the sensor response, including of pigment concentration, temperature, speed and time of stirring in the extraction of the pigments, the amount of doped pigment and Casting and molding type of the monolith were studied and optimized. The response times of the purple cabbage and red beet pigments doped sensors are obtained less than ۲۰ and ۳۰ seconds and linear ranges are obtained in the pH range of ۲.۰۰ to ۱۱.۰۰ and ۸.۰۰ to ۱۲.۰۰ respectively. The relative standard deviation of both sensors with ۷ repetitions is less than ۱% .