Potassium is the principle cation of the intracellular fluid. It is also an important constituent of the extracellular fluid due to its influence on muscle activity. Its intracellular function parallels that of its extracellular function, namely influencing acid-base balance and osmotic pressure, including water retention. l, 2
Elevated potassium levels (hyperkalemia) are often associated withrenal failure, dehydration shock or adrenal insufficiency. Decreased potassium levels (hypokalemia) are associated with malnutrition,negative nitrogen balance, gastrointestinal fluid losses andhyperactivity of the adrenal cortex. 1, 2

In previously described colorimetric methods for determination ofpotassium or sodium, prior deproteinization of serum or plasmaspecimen was required. Our improved method is the direct spectrophotometric measurement of potassium in blood or plasma..