Method and apparatus for measuring pH of low alkalinity solutions

A method for measuring pH of a low alkalinity sample solution, comprising the steps of:

• providing a pH sensor array having a plurality of pH indicator films, each said pH indicator film having a different indicator concentration;
• applying said sensor array to a series of pH standard solutions having fixed and known pH and alkalinity values;
• simultaneously measuring a pH response for each pH indicator film of said sensor array;
• generating a calibration equation for each pH indicator film that provides the apparent pH as a function of said measured pH response, said calibration equations are generated using said measured pH responses for each pH indicator film from said series of pH standard solutions;
• applying said sensor array to a low alkalinity sample solution having an unknown pH and an alkalinity of less than 100 ppm;
• calculating apparent pH values for each film from each corresponding calibration equation and said measured pH response;
• and
• calculating the actual pH value for the low alkalinity sample solution using extrapolation.