Electrochemistry

Coulometry

total charge

primary use - absolute quantification of substance amount

chloride in bodily fluid

Voltammetry

current as function of varying voltage

primary use - identification and quantification of multiple species

heavy metal analysis, redox behavior studies

Potentiometry

voltage between electrodes

primary use - direct measurement of ion activity and concentration

pH measurement, ion selective electrodes for blood electrolytes

Ion Selective Electrodes

membrane-based electrochemical transducers capable of responding to specific ion

Direct ISE

requires no sample dilution
determines activity of ions in plasma water
lipids and proteins have no effect on electrolyte measurement

Indirect ISE

requires sample dilution
interference by hyperlipidemia and hyperproteinemia
reference range 7% higher than direct ISE

Na+ electrode

silicate glass membrane that is permeable to Na ions and excludes other cations

K+ electrode

valinomycin antibiotic membrane that binds K+ and effectively eliminates interference by Na+ and other ions

Ca2+ electrode

calcium di-phosphate membrane that selectively binds calcium ions

Mg2+ electrode

N'N"N-imn-6,1-hexandiyl-tris membranes that specifically interact with Mg2+ ions

pH Measurement

Potential difference is measured and related to ion activity by the Nernst equation

pO2 Measurement

amperometric Clark electrodes

pCO2 Measurement

CO2 is measured by detecting pH changes as CO2 gas diffuses across a gas-permeable membrane