The development of an optical pH sensor based on immobilization of quinizarin (1,4-dihydroxyanthraquinone) on a triacetylcellulose membrane was described. The resulting membrane exhibited fast color change from yellow to violet, while changing the pH in alkaline region. The immobilized quinizarin showed a broader dynamic range from (pH 9.4-11.4) with respect to free form (pH 8.8-10.4). The sensor response was fully reversible and fast (<20 s) under the batch conditions with pH between 7 and 12.5. The sensor showed excellent long term stability (more than three months) and high reproducibility (R.S.D. less than 2%). The Ka values for free and immobilized dye were evaluated and the chemical reactivity of the quinizarin in solution and after immobilization was also described.

The high mortality rate associated with significant bleeding from stress ulceration has promoted efforts to prevent this complication in critically ill patients. Gastric pH is a key factor in the pathogenesis of stress ulceration and maintaining a pH of 4 or greater reduces the risk for development of the gastric ulceration. Our aim was to compare effects of intravenous bolus administration and continuous intravenous infusion of ranitidine on gastric pH in critically ill patients at the intensive care unit (ICU). Twenty patients who met the inclusion criteria were entered this prospective, randomized, cross over study. A total of 1500 gastric pH measurement was obtained for each phase of the study. Continuous infusion of ranitidine maintained a gastric pH greater than 4 over a longer period than that of bolus administration (22.1 hrs vs. 14.2 hrs, respectively; P<0.001). The pH-monitoring device which was made locally, was comparable to a standard international device. This study showed that continuous infusion of ranitidine was more effective than administration of an equivalent dose of the drug by bolus in maintaining the appropriate gastric pH required for the prevention of stress ulceration.