Environmental and security applications have generated major demands for effective field-deployable tools for detecting nitroaromatic compounds, such as chloramphenicol (an antibiotic), parathion (an organophosphate nerve agent), and TNT (2,4,6-trinitrotoluene, an explosive) in a fast, simple, sensitive, reliable, and cost-effective manner. We report here a single-run approach for such a purpose. The reduction potential of different nitroaromatic compounds was found to systematically shift with the substituent group at an electrochemically preanodized screen-printed carbon electrode. The preanodization treatment makes the peak sharp and hence provides a precise way to identify the substituent effect on nitroaromatic compounds. By using potential shifts as analytical characteristics of nitroaromatic compounds, a suitable internal standard can be chosen based on the criteria of well-separated peak potential and rarely found in the real sample of interest. Simply by measuring the ratio of peak currents between analytes of interest and internal standard, the analysis can be done in a single-run measurement. Both the matrix effect and the variation of electrode during the preparation process can be canceled out in this approach and thus allows for a high-precision analysis. Just by placing a 20-microL drop on a single-use amperometric sensor strip incorporating a three-electrode configuration is enough for rapid and sensitive detection of nitroaromatic compounds by square-wave voltammetry. For example, the linear detection range can be up to 100 microM with a detection limit of 0.42 microM (S/N = 3) in the detection of chloramphenicol. This approach was successfully demonstrated in real sample analysis to verify the applicability of the method. The promising performances open new possibilities for rapid determination of nitroaromatic compounds in environmental and biological samples.

Electrocatalytic oxidation of cysteine (CySH) at Nafion/ lead ruthenate pyrochlore (Py) chemically modified electrodes was thoroughly studied. Electrochemical ac impedance spectroscopy analysis indicated the formation of Py microparticles in the interfacial galleries of Nafion. Experiments with benchmark systems of Fe(CN) 6 3-/4-and Ru(bpy) 2+/3+ reveal the suppression of Nafion's anionic character after the in situ precipitation of Py. Michaleis-Menten-type kinetics with the rate determination step of CyS-Py-Ru VI f Py-Ru IV + CyS-SCy was proposed for this catalytic oxidation. The electrocatalytic behavior is further developed as a sensitive detection scheme for CySH by square-wave voltammetry (SWV) and flow injection analysis (FIA). Under the optimized conditions, the calibration curve is linear up to 560 µM with a detection limit (signal/noise 3) of 1.91 µM in SWV. The detection limit can be improved to 1.70 nM (i.e., 24.22 ng in a 20-µL sample loop) in FIA. This is the lowest value ever reported for direct CySH determination without preliminary accumulation.The sulfur-containing molecule cysteine (CySH) plays a crucial role in biological systems, especially in folding and defolding mechanisms. 1 Because CySH possesses a very low molar extinction coefficient, a spectroscopic method is suitable for its detection only with derivatization via the sulfhydryl functionality. 2 Compared to other options, electroanalysis has the advantage of simplicity and high sensitivity. Several electrochemical systems, such as Nafion/Os(bpy) 3 2+ , polycrystalline gold, vitamin B 12 -adsorbed graphite, phthalocyanine (Pc) complexes of Co and Mo, watersoluble Fe and Mn porphyrins, and Ni-Pc immobilized silica gelmodified TiO 2 (ST-NiTsPc) electrodes, were reported for CySH detection. 3-10 Unfortunately, most electrodes contain certain disadvantages to extend them into real application. For example, the Nafion/Os(bpy) 3 2+ electrode showed considerable leaching of Os(bpy) 3 2+ even after it was stabilized in Nafion film. 3 The oxidation process of CySH on polycrystalline gold electrode displayed complicated kinetics and the irreversible adsorption behavior rendered the routine analysis difficult. 4 Although the Pc complexes possess substantial catalytic activity, there is a solubility problem in an acidic environment. The ST-NiTsPc/carbon paste electrode was reported recently to overcome these problems except that the detection range (1-7 mM) is not sensitive enough for real-sample analysis and the interference from other biological chemicals is considerably high. 10

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