VARIABLE SELECTIVITY OF THE HITACHI CHEMISTRY ANALYZER CHLORIDE ION-SELECTIVE ELECTRODE TOWARD INTERFERING IONS

Chloride measurements by ion-selective electrodes are vulnerable to in terference by anions such as iodide, thiocyanate, nitrate, and bromide . We have found that the degree of interference of these anions on the Hitachi chemistry analyzer chloride electrode varies from electrode t o electrode and this variation can even occur within the same lot of m embrane. This variation is not dependent upon the length of time the c artridge has been in the analyzer because no correlation existed betwe en the usage time and the electrode response to interfering ions. Neit her is this variation due to the deterioration of the electrode becaus e all electrodes tested had calibration slopes within the manufacturer 's specification. Our study, however, showed that even after repeated exposure to a plasma sample containing 2 mM thiocyanate, the chloride electrode was still able to accurately measure the chloride in plasma without thiocyanate, thus confirming that a carryover effect does not exist from a previous thiocyanate-containing sample.