Densitometric analysis for quality control in poly(vinyl chloride)-membrane electrode manufacturing

Abstract This paper describes a simple densitometric method which will enable high quality potentiometric ion-selective electrodes (ISEs) to be produced. When assembling double matrix membrane (DMM) technology electrodes, it is critical that the membrane is located for the electrode to function properly. It is, therefore, important that this is monitored during the production process. The membrane must be able to come into contact with the relevant substance to be analysed but it is also important that there is no leakage between the solution and the sensor conductor path. The poly(vinyl chloride)- (PVC) membrane material is inserted into sensor configuration. All manufactured sensors need to be checked so that there is no leakage in the membrane. After the PVC is inserted, it is necessary to perform a densitometric measurement to check that the correct amount of PVC is presented and that it is evenly distributed. A pigment is added to the PVC to enable this to occur. The pigment ensures that part of the light spectrum emitted by the densitometer is absorbed. The reflected light is then analysed to identify both the quantity and location of the PVC. We found that adding a pigment to the PVC-membrane surrounding ammonium-selective electrodes does not change the electrodes electrochemical characteristics.