A salicylate-selective liquid membrane electrode with a nitronsalicylate ion-pair complex in nitrobenzene as the electroactive species is described. At pH 4.5-9.5, the electrode provides a rapid and near-Nernstian response to salicylate ion in the concentration range 10-I-10-4~. The selectivity coefficients obtained for 40 different carboxylate, phenolate and inorganic anions showed that there was negligible interference by most of these ions. In general, the proposed electrode has significantly better performance characteristics than many of the previously described salicylate electrodes. The results obtained for the direct potentiometric determination of salicylate in the range 10 pg ml-1-10 mg ml-1 show an average recovery of 98.9% and a mean standard deviation of 1.8%. Procedures for the determination of salicylate in some keratolytic solutions, ointments, powders and tablet dosage forms containing salicylic acid, methyl salicylate and acetylsalicylic acid are described. The average recovery is 98.3% of the nominal values (standard deviation, 2.1%), which compares favourably with results given by the British Pharmacopoeia method.
Flow injection analysis (FIA) systems incorporating potentiometric sensors for hannine and harmaline hallucinogens are described. The sensors are based on the use of harmine and harmaline tetraphenylborate or reineckate as electroactive compounds dispersed in plasticized PVC matrix. Laboratory-build flow-through sandwich cell equipped with silver disk coated with the sensing material is used as a detector in a low dispersion FIA system. The detector exhibits fast and linear response over the concentration range 10-2-10-6M harmine or harmaline with a detection limit of 2 pg/mL (for 100 pL samples). Operational pH ranges from 3 to 8, sampling rate is 80 per hour and the precision is typically f0.6%. Recovery and reproducibility data agree fairly well with those obtained by gas-liquid chromatography.
The potentiometric response characteristics of a poly(vinyl chloride) membrane electrode for heroin based on its ion-pair complex with tetraphenylborate were examined. The influence of pH, temperature and time on the performance of the electrode system was investigated. The electrode shows a near-Nernstian response over the heroin concentration range 10(-2)-10(-4) M with good precision. The mean relative standard deviation for the determination of heroin in 40 micrograms ml-1(-1) mg ml-1 aqueous heroin hydrochloride solutions is 1.2%. The electrode exhibits good selectivity for heroin in the presence of a number of adulterants and basic organic compounds commonly present in illicit heroin powders. The method was applied to the direct potentiometric determination of heroin in illicit powders (10-36% heroin) and the results agreed fairly well with those obtained by gas - liquid chromatography.
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