The influence of carbon dioxide, bicarbonate and other buffers on the potential of antimony microelectrodes

Antimony microelectrodes were calibrated at 37 degrees C in phosphate buffers, in different bicarbonate solutions at various CO2-partial pressures and in buffers like TRIS1, TES2, MES3 and malonic acid. By use of the latter buffers (with exception of malonic acid) the most reliable calibration curves were obtained ("normal values"). The usual calibration in 67 mmol/l standard phosphate buffers turned out to be unacceptable because the obtained mV-values were too high (negative) in comparison to all other buffers. Different calibration curves resulted from the use of pure bicarbonate solution whether the pH-values were changed by variation of pCO2 or of the bicarbonate concentration. Low bicarbonate concentrations in combination with low pCO2 gave mV-values which were too low relative to the other buffers. Both the increase of pCO2 as well as of the bicarbonate concentration caused a shift of the potential of the antimony electrodes toward "normal values". In solutions containing other buffers the influence of bicarbonate and pCO2 became negligible with increasing buffer concentration. Decreasing oxygen partial pressure was found to cause an increase of the potential of the antimony electrodes. The influence of liquid junction potentials at the reference electrode is discussed.