Construction and characterization of potentiometric sensor for the determination of oxytetracycline hydrochloride

The construction and performance of plastic membrane (PME) oxytetracycline hydrochloride (OTC)-selective electrodes, based on three types of ion-pairs, OTC-tetraphenylborate (TPB), OTC-phosphotungstate (PT) and OTC-silicotungstate (SiT), as the electroactive substance in a plasticized PVC membrane with dibutylphthalate (DBP), were described. Furthermore, internal solid contact sensors (ISCS) OTC-selective sensors, based on a conducting polypyrrole (PPy) film immobilized on a platinum or glassy carbon electrode surface casted by a plasticized PVC membrane were constructed and evaluated. A novel optimization methodology in a numerical expression, comprehensive quality index (CQI) for a sensor, was used to optimize the composition of the membrane in the preparation of PME and screen the parameter of electropolymerization in the preparation of ISCS. Several PMEs and ISCSs were fully characterized and evaluated. An ISCS (Pt/PPy/PVC (OTC-TPB)) showed an excellent Nernstian response over the linear concentration range of 4.0 x 10(-7)-5.0 x 10(-2) M with the slope of 60.6 mV per decade (at 25 degrees C). The limit of detection was 1.0 x 10(-7) M of OTC (0.03 ppm). The response time was <25 s. The sensor was successfully used for the analysis of OTC in pharmaceutical formulation by using direct potentiometry.

Determination of tetracycline antibiotics in beef and pork tissues using ion-paired liquid chromatography

A simplified procedure was developed for determination of tetracycline antibiotics in tissues which improved stability of these compounds in sample extracts and eliminated the need for troublesome cleanup procedures. Tissues were homogenized in water. Acetonitrile (16 mL) and then 1 mL of 0.1 M H(3)PO(4) were added to 4 mL of homogenate and the clear supernatant was filtered. The filtrate was mixed with hexane and dichloromethane and the resulting water layer was collected, evaporated to 1-2 mL, and filtered into autosampler vials. Ion-pairing liquid chromatography was used to separate tetracyclines from interferences in sample extracts, eliminating the need for further cleanup. Analysis was isocratic using a Phenomonex Prodigy ODS(3) column with a mobile phase of 4 mM oxalic acid, 4 mM sodium oxalate, 10 mM sodium decanesulfonate-acetonitrile (70 + 30 for oxytetracycline and tetracycline; 66 + 34 for chlortetracycline). Recoveries were generally in the 90-100% range with limits of quantitation of 0. 05-0.1 ppm. The procedure was evaluated with beef and pork muscle, liver, and kidney.