Problems in the Application of Ion-selective Electrodes to Serum Lithium Analysis

Abstract

Three types of lithium ion-selective electrode (ISE) have been studied in microconduit flow injection analysis for their response to lithium ions in serum samples containing between 0.21 and 2.00 mM lithium. The effects of possible interferents, such as proteins and sodium chloride, in samples have been studied with regard to the poor quality of data. Adjustment of the serum sodium chloride level to 153.9 mM improved the ISE lithium data to match more closely those obtained by flame photometry. Nevertheless, even the best of the three lithium lSEs studied, namely that based on an electroactive component of barium propoxylate, produced data that matched flame photometric data for only five serum samples out of the ten examined. The other two electrode types studied were based on PVC matrix membranes of a commercial lithium ISE (Philips Cat. No. 561-LI) and dodecylmethyl-14-crown-4