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.
