Rapid automated method for on-site determination of sulfadiazine in fish farming: a stainless steel veterinary syringe coated with a selective membrane of PVC serving as a potentiometric detector in a flow-injection-analysis system

Sulfadiazine is an antibiotic of the sulfonamide group and is used as a veterinary drug in fish farming. Monitoring it in the tanks is fundamental to control the applied doses and avoid environmental dissemination. Pursuing this goal, we included a novel potentiometric design in a flow-injection assembly. The electrode body was a stainless steel needle veterinary syringe of 0.8-mm inner diameter. A selective membrane of PVC acted as a sensory surface. Its composition, the length of the electrode, and other flow variables were optimized. The best performance was obtained for sensors of 1.5-cm length and a membrane composition of 33% PVC, 66% onitrophenyloctyl ether, 1% ion exchanger, and a small amount of a cationic additive. It exhibited Nernstian slopes of 61.0 mV decade-1 down to 1.0×10-5 mol L-1, with a limit of detection of 3.1×10-6 mol L-1 in flowing media. All necessary pH/ionic strength adjustments were performed online by merging the sample plug with a buffer carrier of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, pH 4.9. The sensor exhibited the advantages of a fast response time (less than 15 s), long operational lifetime (60 days), and good selectivity for chloride, nitrite, acetate, tartrate, citrate, and ascorbate. The flow setup was successfully applied to the analysis of aquaculture waters. The analytical results were validated against those obtained with liquid chromatography–tandem mass spectrometry procedures. The sampling rate was about 84 samples per hour and recoveries ranged from 95.9 to 106.9%.

A potentiometric magnetic immunoassay for rapid detection of Salmonella typhimurium

Potentiometric detection with homemade polymeric membrane microelectrodes was coupled to a magnetic sandwich immunoassay for Salmonella typhimurium determination. Cadmium and sodium ion selective electrodes were used respectively as indicator and pseudo-reference electrodes and were prepared in pipette tips to allow potentiometric measurements in microliter sample volumes. In the proposed method, the concentration of S. typhimurium was proportional to the amount of cadmium released upon dissolution of a CdS nanoparticle labeled to the secondary detection antibody. The limit of detection was 2 cells per 100 μL. The immunomagnetic assay with potentiometric detection is suitable for sensitive and rapid (average total time per assay of 75 minutes) detection of S. typhimurium in milk samples. The proposed method is easy to perform, safe, sensitive, and low cost and has potential for in situ analysis.