pH buffer accuracy
pH buffer accuracy is essential for a proper calibration, and hence to assure the reliability and quality of pH measurements.
Since the uncertainty of the pH buffers used for calibration has a significant impact on the overall measurement performance, an explorative research project was conducted in order to ascertain the accuracy of these pH buffers. This study, which compares some commercially available buffers (tertiary standard) to secondary DKD standards, revealed unexpected results.
Buffer calibration solutions from seven different providers (including METTLER TOLEDO buffers), with a certified measurement uncertainty of ± 0.02 pH units, were purchased and compared to secondary DKD reference pH standards (pH 4.005, 6.865 and 9.182, which have a measuring uncertainty of ± 0.003 pH units).
All buffers were measured under the same conditions, using a SevenExcellence™ S400 meter with a new InLab® Max Pro-ISM sensor. Three pH buffers from each company were tested in the pH range 4.00 to 10.00. Each solution was measured nine times, for a total of 216 measurements…
pH buffer accuracy
To visually compare the results, the average of the normalized measurement results of the secondary DKD pH reference buffers was used so as to calculate a linear regression. In the following figure, the comparison between values of the commercial buffers and the linear regression from the DKD reference standards can be seen….
It is well known that a pH measurement typically reaches an uncertainty of about 0.05 pH units. The uncertainty brought in by calibration buffers is one of the largest source of error in pH measurement, being normally in a range of ± 0.02 pH units. As the error produced during calibration is transferred to every subsequent measurement made with the relevant sensor, an inaccurate buffer significantly increases the total measurement error…