What is the main reason for KCl addition in the Water Conductivity test for pH measurement?
A. In Stage 3, a neutral electrolyte (KCl) is added to accurately measure the pH of the solution. If the ionic strength of the solution is not increased, the pH measurement will be highly unstable and inaccurate. So KCl is added so that there is minimal concentration gradient across the pH electrode’s membrane between the water and sensor’s internal electrolyte. As a neutral salt, KCl does not impact the pH. It impacts the conductivity of the water, but you do not measure the conductivity again at this stage of the test, only a pH measurement. The method says to use this pH result and the conductivity result from Step 4 (Stage 2), and go to the Stage 3 table. If the measured conductivity from Stage 2 is less than the value in the Stage 3 table (at the measured pH), then you pass. The Stage 1-3 must be done sequentially, otherwise the user will reach wrong conclusions. back to top USP Chapter : Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests Q.
