1. Ion-Selective Electrode (I.S.E.)
Principle of
Ion-Selective Electrode (I.S.E.)
I.S.E. consists of a thin membrane across which only the intended ion can be transported.
The transport of ions from a high conc. to a low one through a selective binding with some sites within the membrane creates a
potential difference.

2. Electrodes and Potentiometry
Use of Electrodes to Measure Voltages that Provide Chemical Information
Various electrodes have been designed to respond selectively to specific analytes
Indicator Electrode:
Electrode that responds to analyte and donates/accepts electrons
Reference Electrode:
Second ½ cell at a constant potential
Cell voltage is difference between the indicator and reference electrode

4. Reference Electrodes Reference electrode, [Cl-] is constant
Potential of the cell
only depends on [Fe2+] & [Fe3+]
Pt wire is indicator electrode whose potential responds to [Fe2+]/[Fe3+]
Unknown solution of
[Fe2+] & [Fe3+]

6. Reference Electrode
Silver-Silver Chloride Reference Electrode

8. Reference Electrode
Saturated Calomel Reference Electrode

10. Types of I.S.E. 2. Solid-state electrode 3. Liquid-based electrode
1. Glass membrane
2. Solid-state electrode
3. Liquid-based electrode
4. Compound electrode

11. Electrolytes Type of ions Cations – Positive charge
move toward the cathode
Na+ = Extracellular cation
K+ = Intracellular cation
Anions – Negative charge
move toward the anode
Cl– Extracellular anion
HCO–3 – Extracellular anion 11

12. Sample Collection Serum Collected in heparin bulb Plain
EDTA can not be use ….?
Urine
Collected in plain Vaccutte 12

13. Routinely measured electrolytes
Sodium
(90%)Major cation
Extracellular fluid outside cells
Normal values
Serum = mEq/L
Urine (24 hr ) = mEq/L
Functions
Influence on regulation of body water
Osmotic activity
Neuromuscular activity 13

14. Sodium (Na) Sodium determination Ion-selective (specific) electrode
Membrane composition = lithium aluminum silicate glass 14

15. Hyponatremia <135 mEq/L
Increased Na+ loss
Aldosterone deficiency = Addision disease
Diabetes mellitus
Diabete Ketoacidosis
Potassium depletion
K normally excreted , if none, then Na
Loss of gastric contents 15

16. Routinely measure electrolytes
Potassium (K)
(2%)major cation
Intracellular fluid inside cell
Normal value
Serum mEq/L
Urine mEq/L
Function
Neuromusculer cells
Heart muscle contraction
Increase K Promotes muscular excitability
Decrease K =Paralysis and arrhythmiasis 16

17. Hypernatremia
Excess water loss resulting in dehydration (relative increase)
Sweating
Diarrhea
Burns
Dehydration from inadequate water intake
Diabetes insipidus 17

18. Hyperkalemia Increased K concentration Causes Renal disease
Acidosis (Diabetes mellitus )
H+ competes with K+ to get into cells & to be excreted by kidneys
Decreased insulin promotes cellular K loss
Hyperosomolar plasma (from ↑ glucose) pulls H2O and potassium into the plasma 18

19. Chloride ( Cl - ) Chloride Major cation Extracelluler fluid
Normal value
Chloride usually follows Na (if one is abnormal, so is the other)
Function - not completely known
body hydration
osmotic pressure
electrical neutrality & other functions 19

20. Chloride ( Cl - ) Normal values Serum – 100 -110 mEq/L
24 hour urine – mEq/L
varies with intake
CSF – mEq/L 20

21. Hypochloremia Decreased serum Cl loss of gastric HCl
salt loosing renal diseases
metabolic alkalosis
increased HCO3- & decreased Cl- 21

22. Hyperchloremia Increased serum Cl dehydration (relative increase)
excessive intake (IV)
congestive heart failure
renal tubular disease
metabolic acidosis 22

23. Advantages of I.S.E.
1 . Linear response: over 4 to 6 orders of magnitude of A.
2. Non-destructive: no consumption of analyte.
3. Non-contaminating.
4. Short response time: in sec. or min. useful in indust. applications.
5. Unaffected by color or turbidity.

24. Limitations 1. Precision is rarely better than 1%.
2. Electrodes can be fouled by proteins or other organic solutes.
3. Interference by other ions.
4. Electrodes are fragile and have limited shelf life.
5. Electrodes respond to the activity of uncomplexed ion. So ligands must be absent or masked. m must be kept constant

25. Functions Volume and osmotic regulation
Myocardial rhythm and contractility
Cofactors in enzyme activation
Regulation of ATPase ion pumps
Acid-base balance
Blood coagulation
Neuromuscular excitability
Production of ATP from glucose 25

26. Application of ISE Electrolyte Arterial Blood Gas Analysis Sodium pO2
Potassium
pCO2
Calcium pH
Lithium
HCO3-
Iodine
Magnesium
Chloride
Fluoride
Glucose
Urea 26