The application of solar UV radiation as sample digestion method is reported. The method is employed in adsorptive stripping voltammetric determination of nickel and cobalt in river water samples. The river water samples were collected from downstream of Warnow River (Germany) and acidified to pH of by addition of ultrapure 65% HNO3. Furthermore, 3.4？mgL？1 ultrapure hydrogen peroxide solution was added to the samples as photochemical reaction initiator. The samples were transferred to UV-A transparent polyethylene terephthalate bottles and put in the sunshine for UV irradiation for six and 12 hours at a UV-A intensity of 3.90？mW/m2. The comparison of the concentration values showed that, 6 hours of solar UV irradiation at 3.90？mW/m2 UV-A intensity is not sufficient to complete the digestion process though it yields much better results than the undigested original sample. However, 12 hours of solar UV-A irradiation under similar conditions is almost as effective as a 30？W artificial UV lamp (254？nm) and can be applied to the digestion of dissolved organic carbon in trace nickel (II) and cobalt (II) analysis in natural waters such as river water, lake waters, and well waters. 1. Introduction The determination of trace metals in natural waters like river water is crucial especially for those metals causing health hazards and environmental effects. Metal pollutants exist bounded by organic and/or inorganic matrices in the environment and thus the determination of these metals in natural waters becomes complicated unless they are separated from the matrices by application of proper sample pretreatment methods [1]. Electrochemical methods and especially the voltammetric determination of metal ions require homogenous samples, free of organic matter which interacts with the metal ions and with the electrode material. Dissolved organic matter (DOM) may form complexes with metal ions preventing them from reduction at the working electrode or shifting the electrochemical redox potential towards negative direction. Such compounds can also affect the determination by interacting with the electrode material forming adsorbed films or changing surface tension. Furthermore, DOM can undergo electrochemical redox reactions at the electrodes leading to increased background currents. Thus, DOM can make the voltammetric determination of trace metals impossible [2]. Methods like wet digestion and dry ashing have been employed for many decades. However, these methods involve high risk of contamination [3] that comes from impurities of the oxidizing agents like mineral acids,
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