From molecular recognition to analytical information using chemical sensors: Development of a combined catheter gastric pH‐probe

The best possible performance of a sensor can be described in terms of information theory according to Shannon, and is based on the reduction in entropy of a system. The relevant quantity is the maximum yield in information. The maximum yield in information can be related directly to the analytical performance and the selectivity of the recognition process. A combined catheter electrode for potentiometric intraluminal pH‐measurement of 3 mm outer diameter was developed and tested in gastric juice. The sensor described is based on the neutral chromoionophore ETH 2418 incorporated into a liquid membrane of variable composition. The sensor was optimized to obtain maximum yield in information relevant to medical intragastric applications. The influence of different types of polymers, plasticizers, additives and carriers, and of varying their concentrations was studied. Studies focused on: extending the dynamic pH range; showing a sufficient pH‐resolution and accuracy by eliminating the interference of the drug Dormicum. The combined catheter electrode showed a wide dynamic range, high long‐term potential stability and good reproducibility, as well as a fast response time in aqueous solutions [15]. The maximum yield in information for 9 decades of H⁺‐activity was calculated as to be 7.94 bits. The loss in information for one decade loss in dynamic range from 9 to 8 decades of H⁺‐activity and constant reproducibility is 0.17 bits. This measure allows the comparison of required and achieved quality of different probes, accuracy not respected.