Abstract
Reliable measurement of pH in dilute and poorly buffered aqueous solutions is problematic. Of particular concern are the errors introduced as a result of differences in ionic strengths between the calibration solutions and the test sample. Residual junction potentials, stream potentials, and the mode of construction of the liquid junction have been implicated. Errors of 0.2 pH units and higher are commonplace. The relative merits of the calibration of various electrode systems with standard buffer solutions, dilute buffers, and dilute hydrochloric acid solutions on the precision and accuracy of electrode responses were investigated. A simplified free diffusion junction reference electrode was developed and tested. The dilute acid calibration technique appears to be significantly more accurate than the calibration with buffers. The free diffusion junction in its present form does not lead to significant improvements in accuracy or reproducibility.
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