SCREEN-PRINTED POTENTIOMETRIC STRIP FOR CALCIUM ION DETERMINATION IN WATER AND MILK

In this study, a novel type of calcium ion potentiometric strip was fabricated using a screen-printing technique. Commercial ink was first printed onto the ceramic substrate in order to construct the reference electrode and working electrode. Then modification of the graphene film on the surface of the working electrode was performed using a one-step electrodeposition technique. A calcium ion-selective membrane was coated onto the surface of the graphene film with a simple drop-casting method. Dynamic response testing was employed to characterize the potentiometric performance of the developed disposable strip, which showed a Nernstian slope of 29.1 mV decade(-1), low detection limit of 10(-5.9) mol L-1, and short response time (less than 10 s). Furthermore, the potential response of the developed strip was insensitive to oxygen, redox species, and light. The use of the disposable potentiometric strip for water and milk sample analysis was performed with a one-point calibration procedure. The detection limits were 8.6 x 10(-5) mol L-1 for tap water samples, 8.2 x 10(-5) mol L-1 for mineral water samples, and 9.8 x 10(-5) mol L-1 for milk samples. This method could be used as an effective tool in real sample analysis, which makes it a promising alternative in routine sensing applications.