EFFECT OF DIFFERENT EXPERIMENTAL PARAMETERS ON THE POTENTIOMETRIC EVALUATION OF BLOOD ELECTROLYTES USING K+ AS A TEST CATION

Potentiometric evaluation of ionic concentrations in physiological med ia has been reported to be significantly affected by the albumin conta ining matrix, Previous studies have attempted to clarify the origin of different patterns of variation of E versus albumin concentration at a constant 0.01 mol dm(-3) KCl, depending on the experimental methodol ogies, This paper reports on measurements of K+ in albumin (BSA) conta ining KCl solutions, which have been pursued following different metho dologies concerning the sequence of measurements, i.e., starting eithe r from the most concentrated solution (100 g dm(-3)) (A) or from the m ost dilute solution (20 g dm(-3)) (B), and solution preparation, (a) d ilution of an initial 100 g dm(-3) albumin solution by successive addi tion of 0.01 mol dm(-3) KCl, (b) concentration of an initial 20 g dm(- 3) albumin solution by addition of solid substance, (c) independent pr eparation of each albumin solution (20, 40, 60, 80 and 100 g dm(-3)) o r (d) preparation of each albumin solution from direct dilution of a 1 00 g dm(-3) stock solution with 0.01 mol dm(-3) KCl, Convenient calcul ations were made and showed a significant contribution of albumin to t he liquid-liquid junction potential, The variation of potential with a lbumin concentration is smaller for hypertonic than for isotonic bridg e solutions, both for the dilution series (A,a and A,d) and for the co ncentration series (B,c and B,d), When the method for increasing the c oncentration is performed by addition of a solid substance to an initi ally diluted albumin (B,b), the slope of the E versus albumin concentr ation plot is larger for hypertonic than for isotonic reference electr olytes. This latter finding is in agreement with Payne's results when ultrafiltration was used to concentrate a protein solution, These obse rvations are a clear indication that the method of preparation of conc entrated protein solutions may significantly affect the results.