Patent ID: 7883898

Claim:
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 pH response, said calibration equations are generated using said 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 preliminary pH values for each film from each corresponding calibration equation and pH response using the equation: pH i =f i ( A i ) where: i is the pH indicator film index, f i is the calibration equation that provides the apparent pH value as a function of pH response for the i th pH indicator film, A i is the measured pH response for the i th pH indicator film, pH i is the apparent pH value calculated from the measured pH response of the i th pH indicator film and the corresponding calibration equation; calculating the actual pH value for the low alkalinity sample solution using the extrapolation equation: pH sample =  ∑ ( In i 2 ) ∑ ( In i * pH i ) ∑ In i ∑ pH i   ∑ ( In i 2 ) ∑ In i ∑ In i N  where: i is the index corresponding to each pH indicator; In i is the indicator concentration of the i th indicator; pH i the apparent pH value calculated from the pH response of the i th pH indicator film and the corresponding calibration curve; and N is number of pH indicators.