Patent ID: 7943391

Claim:
A method of performing in situ continuous autonomous potentiometric pH measurements for extended periods of time comprising the steps of: recording a plurality of potentiometric pH measurements using a potentiometric pH measurement device; autonomously activating a spectrophotometric calibration system positioned within the device wherein the system is activated by an event trigger or a defined time interval wherein the event trigger is a sudden pH change outside the typical deviations of pH recordings; calibrating the potentiometric pH measurement device comprising the steps of: obtaining spectrophotometric pH measurements from a spectrophotometer located within the device comprising the steps of: sampling an aqueous medium; collecting data representative of temperature and salt concentration of the sampled aqueous medium; combining a sulfonephthalein indicator and a first portion of the sampled aqueous medium; delivering the combined medium to an optical cell; obtaining an absorbance spectrum from the combined medium; calculating solution pH of the sampled aqueous medium utilizing the optical absorbance ratios at multiple wavelengths, the temperature, and the salt concentration; obtaining a potentiometric pH measurement of a second portion of the aqueous medium substantially contemporaneously with the spectrophotometric pH measurements; calculating the deviation between the potentiometric pH measurement and the spectrophotometric pH measurement; and adjusting the potentiometric pH measurement device using the calculated deviation, wherein the adjusting calibrates the potentiometric pH measurement device; and recording the calibrated potentiometric pH measurements for an extended period of time until an event trigger or preset time interval autonomously activates the spectrophotometric calibration system to calibrate the device.