Calibration Standards for Multi Ion Analysis in Whole Blood Samples

Abstract

Several analytical devices on the market today are capable of determining various parameters in whole blood with the aid of ion-selective electrodes. These devices are generally suitable for use in intensive care units or in the field of anaesthetics. The results of a measurement can be made avail-able only a few minutes after the sample is taken. The necessary electrode calibrations are generally carried out using a minimum of two standard solutions and the results are used to determine the calibration lines. It has become common practice to perform a one point calibration in addition to every measurement of a sample in order to correct any possible shifts of the electrode potential. For practical and economic reasons, it is customary to use as calibration standards two aqueous solutions having electrolyte concentrations lying approximately within the physiological range of blood serum. Up to the present it has been the practice in clinical chemistry to give the results of electrolyte determinations in the form of concentrations, with the exception of the pH value. However, when a measurement is made with the aid of ion-selective electrodes, it is the activity which is being measured. Errors in the concentration determinations are to be expected:

• 1) if the ionic strenght of the standard solution does not conform to that of the substance being measured, and

• 2) if there are differences in the liquid junction potential between standard solutions and the sample being measured.