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.