Esophageal pH monitoring developed a dependable external reference electrode. Using this technique to monitor esophageal acid exposure patients for periods up to 24 hours, DeMeester and Johnson were able to identify the most important parameters of esophageal acid exposure, and they developed a composite pH score to quantify gastroesophageal reflux. The initial 24-hour pH studies required hospitalization until the introduction of microcircuits in the 1980s that allowed portable esophageal pH monitoring in an outpatient setting. Gastroesophageal reflux disease (GERD) is a common disease in western countries. In the United States, 7% of the population experiences heartburn daily and 44% at least once a
PH cycle, and there is evidence of ongoing ocean acidification caused by carbon dioxide emissions. However, pH measurement is complicated by the chemical properties of seawater, and several distinct pH scales exist in chemical oceanography. As part of its operational definition of the pH scale, the IUPAC defines a series of buffer solutions across a range of pH values (often denoted with NBS or NIST designation). These solutions have a relatively low ionic strength (≈0.1) compared to that of seawater (≈0.7), and, as a consequence, are not recommended for use in characterizing the pH of seawater, since the ionic strength differences