Patent ID: 9274079
Filing Date: 2016-03-01
CPC Classification: G01N

Claim Text:
1. A method of determining a concentration of an etchant product in an alkaline etchant solution comprising a predetermined concentration of a hydroxide compound dissolved in water, comprising the steps of: defining a maximum expected concentration of the etchant product in the alkaline etchant solution; providing a plurality of standard solutions comprising the predetermined concentration of the hydroxide compound and different predetermined concentrations of the etchant product in a range from zero to a maximum expected concentration of the etchant product in the alkaline etchant solution; adding predetermined concentrations of an acid and fluoride ions to each of the standard solutions to provide a plurality of calibration solutions having a pH in the 0.0-3.0 pH range and a concentration of fluoride ions in stoichiometric excess of that required to react with all of the etchant product in an alkaline etchant solution comprising the maximum expected concentration of the etchant product; generating a calibration curve of a concentration of the etchant product versus a potential of a fluoride ion specific electrode (FISE) by sequentially placing the FISE and a reference electrode in contact with each calibration solution and measuring the potential of the FISE relative to the reference electrode via a voltmeter; providing a test solution comprising a predetermined volume of the alkaline etchant solution and the same predetermined concentrations of the acid and fluoride ions as in the calibration solutions; placing the FISE and the reference electrode in contact with the test solution and measuring the potential of the FISE relative to the reference electrode via the voltmeter; and comparing the potential of the FISE measured for the test solution with the calibration curve to determine the concentration of the etchant product in the alkaline etchant solution, wherein fluoride ions are added to the test solution and the calibration solutions as part of a fluoride compound, and the FISE and the reference electrode may be separate electrodes or may be combined in a combination electrode.