Spectrofluorimetric flow-injection determination of potassium in serum based on enzyme activation

A method for the determination of potassium in serum samples based on activation of the reaction between phospho(enol)pyruvate and adenosine diphosphate catalysed by pyruvate kinase is proposed. The strong interference from sodium and ammonium ions on this reaction is avoided by the presence of Li+ and Kriptofix-221 in the samples and a glutamate dehydrogenase reactor, respectively. The high sensitivity of the method makes a 1:100 dilution of the serum samples feasible which minimizes the interference from other species present in serum. The method has been validated by a within-run and between-run study as well as comparison with flame photometric and potentiometric methods applied to 15 serum samples.