New approach for elucidating the oxygen sensitivity and calibration of the antimony electrode.

The biomedical use of the polycrystalline antimony pH electrode is hampered by oxygen dependence and low pH resolution (0.1 pH). Although, the pH resolution is improved by using highly purified crystallographically oriented monocrystalline antimony (COMA), the oxygen effect on the electrode remains. In an in vitro examination of the COMA electrode it was found that the oxygen dependence is similar to that of polycrystalline antimony, i.e. nonlinear with an increase in sensitivity below 10 kPa. These findings imply that the oxygen tension in the vicinity of a COMA pH electrode, has to be known or controllable for the pH reading to be at all valid especially at low oxygen levels, such as is often seen in biomedical applications. A calibration procedure using a zero oxygen solution is used in order to obtain absolute pH readings in a measurement solution of pre-set or known oxygen levels. Furthermore, the nonlinear oxygen sensitivity of the antimony electrode suggests that the underlying electrochemical reactions are other than those described by corrosion theory.