Electrochemical Measurement Systems

Types of Electrodes

• Glass Electrodes
  • H+, Na+, K+, Li+, Ag+ NH4+
• pH Combination Electrodes
• Solid State Electrodes
  • Cl-
• Liquid Ion-Exchange
  • K+ (valinomycin binds K+ in centre ring)
  • Ca2+ (organo-phosphate salt in PVC)
• Compound Gas Electrodes
  • pCO2 (Severinghaus CO2 electrode)
    • CO2 diffuses past first membrane and alters pH of internal bicarbonate buffer → lowers pH
  • pO2 (Clark electrode)
    • o2 reduced at platinum cathode, releasing electrons
• Enzyme Electrodes
  • Non-ionic compounds
  • Glucose, urea, etc.
  • Measure ions generated from enzymatic reactions

Indirect vs Direct Ion-Selective Electrodes (ISEs)

test2

	Indirect ISE	Direct ISE
Principle	Sample is diluted (generally between 1:16 to 1:34) before the ion concentration is measured	Sample is directly measured without a dilution step
Benefits
Limitations