The pH meter measures the voltage potential (mV) difference between the inside of the pH electrode and the outside sample (reference)

Glass pH electrodes develop a voltage across a permeable glass membrane.

The voltage is related to the difference in H+ activity inside and outside the glass.

Electrode Selection

§  Select proper reference for application

§  Select proper junction for application

§  Select appropriate body and membrane profile

•       Standard, semi-micro, micro, rugged bulb, spear tip, flat surface

§  Select appropriate body type

•       Glass body, epoxy body

§  Select refillable or gel filled

Advantages of Thermo’s ROSS electrode

§  Advantages

•       Variety of body styles

•       Very stable reference

•       Fast response

•       Stable to 0.01 pH in 30 seconds over 50 ^oC temperature change

•       Drift less than .002 pH units/day

•       0.01 pH precision

•       No Ag/Cl in reference system

§  Can measure samples containing Cysteine ( milk & milk related products )

§  Better for TRIS buffers

§  Ag⁺ is toxic – Ross is preferred choice for biological samples & culture media

•       Ross electrodes are all double junction – popular choice for non aqueous pH measurements such a titration.