Herein, we report the electrodeposition of a quinone containing diazonium salt onto the surface of carbon paste electrodes (CPE). An extensive characterisation revealed the optimum deposition characteristics to be obtained using Linear Sweep Voltammetry (LSV) over the potential range +400 mV to −800 mV vs. SCE at 100 mV/s, for five sweeps in 0.1 M H2SO4. The corresponding FBRR-modified CPE was cycled in phosphate buffered saline over the potential range +800 mV to −700 mV vs. SCE at 100 mV/s. The anodic peak potential demonstrated excellent stability over 400 cycles and a Nernstian response was recorded (−59 ± 3 mV/pH, n = 39, r2 = 0.99). The continuous monitoring of pH changes within the same solution exhibited Nernstian behaviour also, confirming the efficacy of the FBRR-modified CPEs for in situ pH monitoring. An extensive shelf-life investigation identified retention of FBRR-modified CPEs sensitivity over 28 days when stored under air conditions at 4 °C. The work described within confirms the effectiveness of FBRR-modified CPEs to perform continuous pH monitoring over a small pH range of physiological relevance.