RUBIDIUM ION-SELECTIVE ELECTRODE FOR THE ASSAY OF POLYENE ANTIBIOTICS

The preparation of a rubidium ion-selective electrode is described. The performance characteristics of the electrode are such that it can be used as an alternative to atomic absorption spectrometry in the assay of bulk nystatin, by measuring the rubidium ion efflux from specially prepared yeast cells. The electrode simplifies assay procedures because rubidium(I) can be determined directly in cell suspensions without prior centri-fugation; assay time is reduced to 10 min. The sensitivity of the method is 2 units of antibiotic per ml, which is comparable with other physico-chemical methods of bioassay but some 10 times more sensitive than the conventional agar diffusion assay. © 1979.