Spectrophotometric Determination of pH

Water chemistry measures minute changes in concentrations (often at the milli/micromolar scale) and pH. Traditional methods (electrochemical probes) to determine pH have uncertainty ranges on the scale of tenths or hundredths, and are therefore not reliable methods to determine changes in microscale processes. This project deals with the use of a spectrophotometer to determine pH, which research has shown to have uncertainty in the thousandths or ten-thousandths. In addition, the data from spectrophotometers is generated from an input (wavelength) and an output (absorbance), which allows for more rigorous analytical techniques. When using pH probes, uncertainty is only observed and measured, but by using spectrophotometry to determine pH, we use calculations that must incorporate uncertainty. These calculations confront students with more authentic and challenging methods to analyze their results and build on analytical techniques used in the Mitch lab at Stanford University.