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 ^o C 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.