An embodiment provides a probe, including: an ion selective shell that includes a pH electrode bathed in an electrolyte and/or buffer solution; a plurality of conductive electrodes coaxially arranged respective to the pH electrode; the plurality of conductive electrodes being electrically isolated on a substrate displaced between the pH electrode and a reference electrode, and including: at least a first conductive electrode that is exposed to sample fluid at a terminal end of the probe proximate to the ion selective shell and disposed on the surface of an electrode substrate proximate to a terminal end of the reference electrode; and at least a second conductive electrode that is exposed to the sample fluid at the terminal end of the probe proximate to the ion selective shell and disposed on the surface of an el electrode substrate proximate to the terminal end of the reference electrode; the probe further including the reference electrode arranged about and along a longitudinal axis of the probe and bathed in a reference buffer and/or electrolyte solution. Other aspects are described and claimed.