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Voltammetric behavior of selected biologically active organic nitro compounds, namely 2-nitrofluorene, picric acid (2,4,6-trinitrophenol) and metronidazole, has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam composite electrode (p-AgSA-CE). The optimum conditions have been found for their determination in a 1 : 1 mixture of methanol and aqueous Britton-Robinson buffer of pH 5.0 for 2-nitrofluorene and in the aqueous Britton-Robinson buffer solutions of pH 2.0 and 4.0 for picric acid and metronidazole, respectively, with the limits of quantification (L Q s) 4, 0.1 and 2 mmol L À1 (DCV at p-AgSA-CE) and 3, 1 and 4 mmol L À1 (DPV at p-AgSA-CE) for 2-nitrofluorene, picric acid and metronidazole, respectively. An attempt to increase the sensitivity using adsorptive stripping voltammetry was not successful for all three test substances. For comparison, the UV-vis spectrophotometric determinations of studied compounds have also been carried out in methanol for 2-nitrofluorene (L Q % 1 mmol L À1) and in deionized water for picric acid). Practical applicability of the newly developed voltammetric methods was verified on direct determination of the studied compounds in drinking and river waters with L Q s around 10 À6 mol L À1 for all the studied compounds.

This paper presents polymer graphite (PG) as a novel material for the scanning tunneling microscopy (STM) probe. Conductive PG is a relatively modern nanocomposite material used for micro-pencil refills containing a polymer-based binding agent and graphite flakes. Its high conductivity and immunity against surface contamination, with a low price, make it seem like a highly suitable material for electrode manufacturing in general. For the tip production, three methods were developed and are further described in the paper. For the production, three commercially available polymer graphite rods were used. Each has been discussed in terms of performance within the tunneling microscope and within other potential applications.

The use of a silver solid amalgam working electrode for HPLC with electrochemical detection has been investigated. The thin-layer and wall-jet detectors based on this electrode were constructed and applied for the determination of a mixture of nitrophenols. The optimal separation and detection conditions for the determination of 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2-methoxy-5-nitrophenol in mixture were found using RP-HPLC at Nova-Pack C18 column and amperometric detection with the above mentioned detectors. It has been proved that the silver solid amalgam electrode is a suitable working electrode for HPLC-ED and provides sufficient sensitivity for determination of tested nitrophenols.

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