Elimination of the erythrocyte effect on the liquid junction potential in Potentiometric measurements on whole blood using mixed salt bridge solutions

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Abstract
An effect of erythrocytes on the liquid junction potential of the junction “concentrated KCl ‖ whole blood” has previously been described, the effect being a positive bias of +1,4 mV with a high erythrocyte volume fraction (0.75). We have studied the erythrocyte effect with different concentrated salt solutions, and found a similar positive bias with KBr, KJ, KNO3, K2SO4, but a negative bias with NaCl, NaNO3, LiCl and CaCl2. The erythrocyte bias may be eliminated by mixing salts with opposite effect, e.g. KCl + NaCl (1.0 + 7.0 mol/1), KNO3 + NaNO3 (1.0 + 3.0 mol/1) KNO3 + Li-acetate (0.15 + 4.0 mol/1). The use of a mixed salt bridge solution may be advantageous for eliminating the erythrocyte bias when measuring ionic activity (e.g. Na+, K+, Ca2+) directly in whole blood.

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