Most resources on pH and the electrochemistry behind it that I've found are IMHO too superficial. For example, they explain that an electrode with less than 80% slope should be discarded, but not why the decrease in slope happens, or why it's a problem if you can just calibrate it. Or they explain the potential generated at the Ag/AgCl eletrode and the glass membrane potential, but not the interaction between the two - does the H+ combine with the e- from the electrode? And what happens if the current is reversed? After reading for a few days I still feel like I don't understand any of it.
So far I've read a couple PDFs on nico2000.net (the 30 page Introduction to pH measurements), the 160 page book pH Measurements by C. Westcott (1978), a few manufacturer's guides to pH measurement theory and practice (by Radiohm, Emerson, Mettler) and the relevant chapters in the Analytical Chemistry books that my library had.
All help appreciated!