Effect of condensation phenomena on potentiometric measurements.
Results of potentiometric analysis, namely those of pH measurements, depend on temperature control of the experimental setup, as it is expressed in the analytical law, the Nernst equation, starting from the primary level, where reference values are conventionally assigned to standard solutions, through the whole traceability chain, down to the service laboratory. Fundamental studies of pH standards, based on the measurement of the potential of an electrochemical cell without transference, known as Harned cell, containing a platinum-hydrogen electrode and a silver-silver chloride reference electrode, refer condensation phenomena on the portions of the cell walls which are not immersed in the thermostatic bath, as one of the major sources of error in the assessment of both the silver-silver chloride electrode standard potential and on pH values. In this work such effect, which is bound to happen due to significant temperature differences between the ambient air temperature and the water bath, has been quantified, presenting an original contribution to the improvement of the quality of potentiometric analysis results. This was possible due to the availability of a climatic cabin "WALKIN" with a temperature control of +/-0.01 degrees C, which permitted that temperature gradients were built between the thermostat water bath (controlled to +/-0.005 degrees C) where cells filled to about 2/3 full were immersed up to 90% of their height, and the surrounding environment.
Lito
M J Guiomar H M
MJ
Faculdade de Farmácia da Universidade de Lisboa, Portugal. mjglito@ff.ul.pt
Camões
M Filomena
MF
Viçoso
Catarina M
CM