This work presents a new differential potentiometric cell for the standardization of pH buffer solutions and its evaluation, by means of a bilateral interlaboratory comparison, in relation to a traditional Baucke cell. The results obtained with the two cells were exactly the same for three of the pH buffer solutions analyzed (1.68, 4.01, and 6.86) and similar to each other for the remaining buffer solution (9.18). The new cell showed an average measurement time of only 21 minutes, in comparison with one to three hours for other cells described in the literature (including the Baucke cell).
pH and electrolytic conductivity are important metrological quantities for several areas of industry. To get reliable results it is necessary to calibrate measuring instruments and devices regularly. For this purpose certified reference solutions are needed. DKD-K-06901 is a manufacturer of certified reference solutions and offers calibration services in the field of analytical chemistry. There are three accredited calibration procedures for the determination of pH used by ZKM -ANALYTIK -GmbH. A new calibration procedure for electrolytic conductivity was established by experts in DKD-K-06901 as the result of a development project in cooperation with National Metrology Institutes. The validation of all procedures is guaranteed by the participation in national and international comparison measurements. Furthermore DKD-K-06901 is actively involved in the work of technical and standardisation committees for developments of analytical quantities.
Zusammenfassung DerpH-WertisteinewichtigeMessgröße zur Charakterisierung von wässrigen Lösungen und damit auch von biologischen Systemen. Von wenigen Ausnahmen der spektroskopischen Bestimmung abgesehen, wird der pH-Wert einer Lösung potenziometrisch, durch Messen der Kettenspannung einer pH-Messkette mit Glaselektrode mit Hilfe einer geeigneten pH-Messeinrichtung bestimmt. Eine Aussage darüber, ob der gemessene pH-Wert den Ansprüchen an die jeweilige Anwendung genügt, ist nur möglich, wenn die Zuverlässigkeit des Messergebnisses durch die Angabe einer Messunsicherheit belegt werden kann. In dem Beitrag wird die Rückführungs-kette für die Messgröße pH-Wert beschrieben sowie einzelne Unsicherheitsbeiträge betrachtet, die der Anwender bei der Einführung und bei der Bestimmung der pH-Werte berücksichtigen sollte. Das schließt auch die technischen Parameter, die an das Produkt gestellt werden, ein.Summary The pH value is an important quantity used to characterize aqueous solutions including biological media. There are only few fields of application for spectroscopic pH measurements. pH is usually measured electrochemically by potentiometry. The cell voltage of a pH measuring chain with glass electrode is measured by means of an appropriate pH measuring device. To be able to assess whether the result of a pH measurement meets all requirements a statement of the measurement uncertainty is mandatory. In the following the metrological traceability chain for pH is described. The paper will focus on important uncertainty contributions to be taken into account by the user. This especially includes technical product parameters.Schlagwörter pH, Kalibrierung, Rückführung
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