This coulommetry calculation does give an upper limit to the concentration of silver in the EIS. We still need a direct, empirical method to measure Ag+ concentration, though. This might be done by titrating EIS with dilute HCl (e.g. 1 to 10 millimoles per liter) and using the extremum value of conductance as the end-point indicator of the titration. A TDS meter might suffice to indicate this conductance turn-around point.
Matthew
