CHEMISTRY
Detection of Potassium in Plasma and Red Blood Cells Using Pulsed Chronopotentiometry.
BENJAMIN STEVENS* and KEBEDE GEMENE. Department of Chemistry, Northern Kentucky
University, Highland Heights, KY 41099.
To date, measurement of extracellular potassium in plasma/serum had been of utmost
interest in clinical diagnosis and this has been accomplished, typically, by direct (classical)
potentiometry with ion-selective electrodes. Recently, it was reported that, in addition to plasma
potassium, measurement of red blood cell (RBC) potassium can be used for assessing the risk,
development and treatment of hypertension. Obviously, the RBC potassium is not accessible to
direct potentiometry. We report here a simple and fast method called pulsed
chronopotentiometry for measurement of potassium in plasma and RBCs simultaneous. Here, a
controlled current pulse is applied across a potassium ion selective membrane to cause extraction
of potassium from the sample into the membrane. This causes depletion of the ions locally at the
membrane surface on the sample side at a given time called transition time. This transition time
is a function of concentration according to the well-known Sand Equation and is clearly observed
by inflection point on the potential-time curve (chronopotentiogram). To assess plasma and RBC
potassium, first, transition time for the plasma potassium is measured. Then, nonionic surfactants
such as Triton X-100 and Brij 58 are added to lyse the RBCs, while the measurement is
underway, and a new transition time, which is a function of potassium ion concentration in the
lysed blood, is observed. Finally, the RBC potassium concentration is easily mathematically
computed from the difference in the transition times observed before and after the cell lysis.