Solar UV Photooxidation as Pretreatment for Stripping Voltammetric Trace Metal Analysis in River Water

The application of solar ultraviolet radiation as sample pretreatment or preparation step in stripping voltammetric analysis of trace metals in presence of low levels of dissolved organic carbon (DOC) natural water samples (river water) was studied. River water samples were collected from downstream of Warnow river (Germany) and acidified to pH of 2±0.2 (by addition of 1 mL of ultrapure 65% HNO3 per liter sample). Furthermore, 100 μL/L of hydrogen peroxide solution (ultrapure, 30% H2O2) was added to the samples as photochemical reaction initiator. The samples were transferred to polyethylene terephthalate (PET) bottles and irradiated with solar radiation of UV-A intensity of 3.6 mW/m2 for six hours, and the concentrations of Zn, Cd, Pb, and Cu were determined by differential pulse anodic stripping voltammetry (DPASV). The comparison of the values with the results obtained for the original untreated sample and artificial UV-treated one proved that solar UV radiation can be applied to the digestion of dissolved organic carbon in trace metal analysis in natural waters like river water, lake waters, well waters, and so forth

H/D Isotope Effects on Redox-Switching of DNA Self-Assembled Monolayers Observed by EQCM and Cyclic Voltammetry

An electrochemical quartz crystal microbalance (EQCM) was employed to study the interactions of hexammine ruthenium(III) (RuHex) and hexammine cobalt(III) (CoHex) with a mixed self-assembled monolayer of single-stranded DNA and 6-mercapto-1-hexanol (ssDNA/MCH SAM) immobilized on gold electrodes. When the buffer medium was switched to deuterium oxide (D2O) from normal water (H2O), we observed a pronounced H/D kinetic isotope effect where a consistent shift of up to 400 mV was seen for the reduction peak potential of CoHex but not with RuHex. This was attributed to a 2400-fold change of the apparent reaction rate constant. Though there was a dramatic increase in the EQCM frequency response at a millisecond time scale in the presence of both redox indicators, compared to the signal observed in a low ionic strength buffer (10 mM tris(hydroxymethyl)aminomethane (Tris)/H2SO4 at pH 7.5), a 10 Hz decrease in the frequency shift was observed upon switching from H2O to D2O-based buffer medium. The hydrogen bond network within the ssDNA layer seems to amplify the H/D isotope effect with CoHex. Amplified isotope effects may play a role in living systems. The mechanisms of recently reported H/D isotope effects in medicinal and biochemistry are still widely unclear. Voltammetric and EQCM studies of H/D isotope effects can provide a platform to investigate amplified isotope effects not only with DNA layers, but probably also with proteins and small organic molecules and may be useful for studies of cell proliferation, as well as drug testing

Solar UV-treatment of water samples for stripping-voltammetric determination of trace heavy metals in Awash river, Ethiopia

We report about testing a new mobile and sustainable water sample digestion method in a preliminary field trial in Ethiopia. In order to determine heavy metals at the ultra-trace level by stripping voltammetric techniques in water samples from Awash River, we applied our new method of solar UV-assisted sample pretreatment to destroy the relevant interfering dissolved organic matter. The field tests revealed that 24 h of solar UV irradiation were sufficient to achieve the same sample pretreatment results as with classic digestion method based on intense and hard UV. Analytical results of this study suggest that both a hydroelectric power station and agrichemical applications at Koka Lake have increased the levels of the investigated metals zinc, cadmium, lead, copper, cobalt, nickel, and uranium