pH electrodes for bio samples

[D. Jacobson]

I found a site which shows a wide variety of pH electrodes for 
biological samples including a micro pH electrode which can measure down 
to 5 microliter samples such as NMR tubes and 96 well plates, a pH 
electrode specifically designed for isoelectric focusing, a calomel pH 
electrode for tris buffers, a spear tip pH electrode for tissue samples, 
and a renewable junction pH electrode which can measure very dirty bio 
samples without fouling.  To get more information click 
http://www.laboratorymart.com/ph/phelectrodes.htm