CLASS AND ANTIMONY ELECTRODES FOR LONG-TERM PH MONITORING - A DYNAMICIN-VITRO COMPARISON

Objective: To compare the performance of combined glass microelectrode s with monocrystalline and polycrystalline antimony electrodes with ex ternal reference in a 24-h dynamic in vitro study. Design and methods: In an artificial stomach, the pH of the contents titrated from pH 1-7 and back by NaOH and HCl was simultaneously measured at 37 degrees C with antimony and glass probes connected to three recording devices. T he recorded data were compared with data monitored continuously by a l aboratory pH measurement system. The sensitivity and drift of glass mi croelectrodes were also analysed in intensive-care unit patients durin g intragastric pH monitoring for up to 96 h. Results: The sensitivitie s of antimony polycrystalline, monocrystalline and of glass electrodes were 54.6, 55.3, and 61.8 mV/pH, respectively. The hysteresis was 6.4 , 7.2 and 2.75 mV for antimony polycrystalline, monocrystalline and fo r glass electrodes, respectively. The drift in 24 h was -0.1 pH for gl ass over the pH range 1-7, and +0.3 pH over pH 1-2.5, and +0.15 pH ove r pH 2.5-7 for both of the antimony electrodes. The response times of both antimony and glass electrodes were similar over the pH range 2.5- 7. The difference in the percentages of time below pH 1.5 was signific ant: 28.2% for glass, 17.3% for antimony polycrystalline and 18.1% for monocrystalline electrodes, respectively (P<0.05). However, the diffe rence in the percentages of time below pH 4 was not significant. After 96 h intragastric pH monitoring in six intensive-care unit patients, the mean drift of glass electrodes was 0.15 pH (range, pH 0.1-0.2) and the mean change in sensitivity 1.2%. Conclusions: (1) Antimony electr odes may be acceptable for intra-oesophageal pH monitoring but are not suitable for intragastric use. (2) The use of glass microelectrodes i s recommended for intragastric pH monitoring, particularly when extend ed monitoring over periods longer than 24 h is required.