Blood plasma is the solution remaining after cells (red, white, etc...) are remo
ID: 827990 • Letter: B
Question
Blood plasma is the solution remaining after cells (red, white, etc...) are removed from whole blood. The clinical analysis of free calcium in plasma can be down with a calcium liquid membrane ion-selective electrode. When combined with a proper reference electrode, the calcium ISE gave the following potentials in a buffered solution:
0.00240 M E= 0.243V
0.000160 M E= 0.208V
1. What is the concentration of calcium in the blood plasma? Use the cell potentials when calculating.
2. Describe the chemical makeup of the liquid membrane of the blood plasma?
Explanation / Answer
What is calcium ion selective electride:
The Calcium Ion Selective Electrode consists of an electrode body containing an ion exchanger in a sensing module. This sensing module contains a liquid internal filling solution in contact with a gelled organophilic membrane containing a calcium ion selective exchanger .
An electrode potential develops across the membrane. When the membrane is in contact with a calcium
solution. Measurement of this potential against a constant reference potential, using an ISE Amplifier and Science Workshop interface, depends on the level of free calcium ion in solution. The level of calcium ions, corresponding to the measured potential, is described by the Nernst equation:
E = E0 + S log X
E = measured electrode potential
E0 = reference potential (a constant)
S = electrode slope (~26 mv/decade)
X = level of calcium ions in solution
The activity, X, represents the effective concentration of the calcium ions in the solution. Total calcium
concentration, Ct includes free calcium ions, Cf plus bound or complexed calcium ions, Cb , since the calcium electrodes only respond to free ion, the free ion concentration is: Cf =Ct