Abstract: A new PVC lithium ion-selective microelectrode based on potassium tetraphenylborate(KTPB) or sodium tetraphenylborate (NaTPB) and plasticized by di-(n-octyl)-phenylphos-phonate (DOPP) has been constructed. The microelectrode based on KTPB has lower detection limit and better selectivity characteristics for bivalent ions, but the microelcetrodebased on NaTPB has lower membrane resistance. The response characteristics of microelectrode for different concentrations in Li⁺ has been examined experimenetally in synthetic in-tracellular solution,serum and physiological saline.

Key words: Ion selcctive microelectrode, Tetraphenylborates, Biological body fluids