medical laboratory technology

1. Potentiometry
Adarsh Benny

2. principle
•It is based on the measurement of potential
difference between two electrodes
immersed in a solution, under the condition
of zero current

3. •Potential difference = E ind - E ref + E lj
• E lj- liquid junction potential
• E ind- indicatoe electrode potential
• E ref- reference electrode potential

4. •Nernst equation
• Ecell= E cell – (2.303RT/nf) Log Q
• R- gas constant
• T- Temperature
• F- faradays constant
o

5. •2 electrodes
1) Reference electrode
2) Indicator electrode

6. 1) Reference electrode
• It is used as a fixed reference for measurement of potential
• Ideal Reference electrode
-should be stable
-ease of fabrication
Eg.
1. Standard hydrogen electrode
2. Silver/silver chloride electrode

7. 2) Indicator electrode
•Reflects activity of the analyte, not the other
compounds in sample
•Eg. Ion selective electrode (ISE)

8. applications
•Measurement of pH
•Measurement of pCO2
•Measurement of Na+, K+, Ca++

9. Ion selective electrode (ISE)
•ISE consist of a thin membrane, across which
selective ions only transported
•The transport of ions from higher conc. To lower
conc. Creates a potential difference
•It is measured by voltmeter

10. V
Reference
electrode
indicator
electrode
Fill solution
sample
Fill solution
Ion
selective
membrane
voltmeter

11. Assignment
Mass spectrophometry