INFLUENCE OF SILVER SALTS IN THE POLYMER MEMBRANE OF POTASSIUM-SELECTIVE ELECTRODES

The influence of the addition of silver tetrakis(4-chlorophenyl)borate to the polymer membrane of potassium-selective electrodes has been investigated. In comparison to the conventional potassium-selective electrodes freshly prepared silver salt sensors show slightly worse slopes, linear ranges and limits of detection. An improvement of these electrode characteristics can be observed after a longer storage time. In this case the silver salt containing electrodes present even better results than the unmodified electrodes. The considerable disadvantage of this silver modified PVC membrane composition is the poor selectivity versus pH and ammonium and the long response time in chloride solutions. These ions cause a strong drift which can be explained by chemical reactions of silver ions occurring at the phase boundary solution/PVC membrane. The same results have been obtained with potassium-selective coated-film electrodes, which have been prepared by dip-coating of epoxy structures covered with silver pads into the ion-selective membrane cocktail.