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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.
