A new optical pH sensor based on a mixture of Alizarin and Orange dyes immobilized on an agarose membrane

Two techniques, including chemical immobilization of a combination of two indicators of Alizarin and Orange dyes and the epoxy activation of the agarose membrane, were used for the preparation of a new optic pH sensor. For this purpose, the mentioned dyes were immobilized on agarose support activated by an epoxy, followed by optimizing the impacts of the coupling pH, as well as the ratio and concentration of the two dyes. The sensor was set up in a flow cell and effectively employed for online pH calculations. The new optic pH sensor could be applied between 4.5 and 11pH values. The sensor could quickly respond to pH alterations in nearly 25 s. The sensor's response is adjustable and replicable. Ionic strengths of up to 0.5 mol L^-1 could have no meaningful impact on the response signal. In addition, no proof of any signal drift or dye leaching was detected over a three-month period.•The chemical immobilization of two indicators on agarose membranes activated by an epoxy could lead to a sensitive optic pH sensor for a wide range of pH.•The intended sensor was mounted in a flow cell and effectively utilized for the purpose of online pH measurement.•The suggested optode was employed to determine pH in real samples of water.