Plasticized poly(vinyl chloride) membrane electrode for the determination of quinine in soft drinks

Easily prepared poly(vinyl chloride) (PVC) membranes based on lipophilic derivatives of teraphenyl borate for the determination of quinine are discussed. It is shown that the membrane preparation does not require a separate precipitation of a quinine-borate ion-pair. Different membrane compositions, including various plasticizers and borate derivatives were examined. Electrodes with potassium tetrakis(4-chlorophenyl borate/didecyl phthalate) (KTpClPB/DDP)/PVC membranes were used to determine quinine in real samples. The electrode exhibited a Nernstian response over the range 0.01-10 mm quinine with a detection limit of 6.3 muM. The optimum operating pH range was 4.4-8.0. Selectivity towards inorganic and organic substances was investigated. The determination of quinine in soft drinks were performed successfully in the presence of ascorbic, citric and benzoic acids and colored matter. The results were verified using a spectrophotometric technique. (C) 2001 Elsevier Science B.V. All rights reserved.