An electrochemical sensor consisting of a screen-printed carbon electrode (SPCE) modified with graphene oxide-poly(acrylic acid)palladium nanoparticles (GO-PAA-PdNPs) was developed for the nonenzymatic determination of glucose by flow injection amperometry (FI-Amp). PdNPs were synthesized on GO-PAA by electroless deposition. The surface morphology of the modified electrode was characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical behavior of glucose on the different modified surfaces was studied by cyclic voltammetry and amperometry. The GO-PAA-PdNPs-modified SPCE showed excellent electrocatalytic performance for the oxidation of glucose. To achieve the optimal electrocatalytic oxidation of glucose by the GO-PAA-PdNPs/SPCE, the applied potential, sample volume and flow rate of the FI-Amp system were optimized. Under the optimal conditions, the current response when the glucose standard was injected provided a detection limit of 22 μmol L −1 , a limit of quantitation of 76 μmol L −1 and two linear ranges, 50 to 15,000 μmol L −1 and 15,000 to 60,000 μmol L −1 . This sensor had excellent sensitivity as well as good repeatability and selectivity. The sensor was applied to detect glucose in biological fluid samples, and the results were in good agreement with those obtained by the standard hexokinasespectrophotometric method.

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A simple, rapid, and environmentally-friendly spectrophotometric method for nitrite detection was developed. Detection was based on a redox reaction with iodide ions in an acidic condition. The reaction was evaluated by detecting the increase in absorbance of the colored product of iodine at 362 nm wavelength. To obtain a good spectrophotometric performance, the iodide ions concentration, hydrochloric acid concentration, and reaction time were optimized. In the optimal condition, the developed spectrophotometric method provided a linear range of 0.0625 to 4.00 mg L−1 (r = 0.9985), reaction time for 10 min, a limit of detection of 25 µg L−1, and a limit of quantitation of 85 µg L−1. This method showed good repeatability (RSD < 9.21%), high sample throughput (9 samples min−1), and good accuracy (recovery = 88 ± 2 to 99.5 ± 0.4%). The method has the potential to be used in crime scene investigations as a rapid screening test for gunshot residue detection via nitrite detection.

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A simple and highly sensitive electrochemical sensor was developed for adsorptive cathodic stripping voltammetry of alprazolam. Based on an electrochemically pretreated glassy carbon electrode, the sensor demonstrated good adsorption and electrochemical reduction of alprazolam. The morphology of the glassy carbon electrode and the electrochemically pretreated glassy carbon electrode were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrochemical behaviors of alprazolam were determined by cyclic voltammetry, and the analytical measurements were studied by adsorptive cathodic stripping voltammetry. Optimized operational conditions included the concentration and deposition time of sulfuric acid in the electrochemical pretreatment, preconcentration potential, and preconcentration time. Under optimal conditions, the developed alprazolam sensor displayed a quantification limit of 0.1 mg L−1, a detection limit of 0.03 mg L−1, a sensitivity of 67 µA mg−1 L cm−2 and two linear ranges: 0.1 to 4 and 4 to 20 mg L−1. Sensor selectivity was excellent, and repeatability (%RSD < 4.24%) and recovery (82.0 ± 0.2 to 109.0 ± 0.3%) were good. The results of determining alprazolam in beverages with the developed system were in good agreement with results from the gas chromatography–mass spectrometric method.