The response of a pH electrode can be modeled as a first order or second order passive low pass filter (i.e. two RC circuits in series). A limitation of commercial pH electrodes is their slow response time, which is typically 2 seconds (i.e. = 2 s).
Analytically, find the transfer function, H(s), of this electrode. This transfer function is defined as the measured pH (output) divided by the actual pH (input).