Design of a simple optical sensor for the detection of concentrated hydroxide ions in an unusual pH range

The failure of conventional electrochemical sensors at pH 9 and above necessitates research into suitable sensor materials and novel sensor chemistries for reliable process monitoring in extremely alkaline media. A novel sensing chemistry for high hydroxide monitoring is reported using 2-pyridylazo compounds doped in polystyrene films. Spectroscopic experiments demonstrate that the absorbance properties of 1-(2-pyridylazo)naphthol in polymeric media could be used to produce a reliable hydroxide sensor. When tested for continuous measurements in relatively high temperature and highly alkaline electroless gold plating baths, the sensor exhibits adequate reversibility, a response time of seconds and a standard deviation of 2σ at the 99.7% confidence interval.