Non-invasive measurement of electrical conductivity of liquids in biocompatible polymeric lines for hemodialysis applications

A non-invasive impedimetric sensing system measuring electrical conductivity of liquids in hemodialysis machines for continuous monitoring applications is introduced. Starting from the typical architecture of the capacitively coupled contactless conductivity approach, we developed an easy-to-use impedance spectroscopy model based on the constant phase element to quantitatively measure the conductivity of liquids in polymeric lines. We also show the experimental setup to determine the parameters of such a model to better cope with the application constraints. We demonstrated that this approach could be used to design conductivity sensing systems to be fit into the typical dimensions of the standard instrumentation for hemodialysis. Experimental results on saline solutions and blood-mimicking fluid report estimated conductivities with root-mean-square error of ≃0.05 mS/cm, corresponding to about 0.5% of the full scale.