Try to get the Cole Parmer 1997-1998 catalog; there's a lot of theory on pH
and conductivity measurement in it, including temperature corrections and
the like; they also have al kinds of pH electrodes (with and without
termistor, for lab use or for field use, etc. etc. - more than 100 different
types), although I think they are rather (very) expensive with their
products..... I've seen the same products elsewhere at 50% or less of their
listed prices (I think they must have the Government as their biggest
customers..... !!!)
I also found somewhere on the web schematics of an amplifier for pH
electrodes, but don't remember the URL. Try a search on Yahoo or Hotbot....

Albert Smulders
InSAD - Encarnaci—n, Paraguay
insad@itacom.com.py