Development of Sensor Calibration against Standards using Measurement Software TestPointTM-CEC and Application to the Verification of pH Electrodes

Abstract

The acquisition, processing and presentation of data from many commercial devices have been simplified by use of personal computers (PCs) and effective software in last decades. As compared to text-based languages, such as BASIC, dataflow programmation (LabVIEWTM) and graphical programming (TestPointTM) have been developed and widely used in diverse scientific fields. Here, TestPointTM is used to control via IEEE-488 interface a system voltmeter; pH measurement is a master variable in analytical chemistry and environmental studies. For precise and accurate measurements of pH, timely verification and calibration of pH electrodes are essentially required. However, the sensitivity of most commercial pH-meters (0.1 mV) is not high enough to check the deviation with respect to Nernst’s law. With this combination of a high resolution voltmeter and graphical programming, data are acquired and processed as follows: a moving average is computed to check if equilibrium is attained and statistical tests are performed to define the confidence interval of the slope of the regression straight line. This allows the user to compute the deviation from the ideal law, generally statistically significant and to verify pH electrodes against NBS standards, according to IUPAC recommendations. A control chart can be easily drawn to define when the electrodes must be replaced. The method and the code can be easily modified to calibrate other sensors.