Polarographic determination of DNA based on its interaction with the phenanthroline-zinc(II) complex

By using the linear sweep voltammetric technique, a phenanthroline (Phen) and zinc(II) (Phen-Zn(II)) complex was used as the electrochemical probe for the determination of double-stranded (ds) DNA. In pH 9.0 Britton- -Robinson (B-R) buffer solution, Phen can interact with Zn(II) to form a stable electroactive [Phen-Zn(II)] complex, which had a sensitive second order derivative polarographic reductive peak at -1.300 V (vs. SCE). After the addition of dsDNA into a solution of Phen-Zn(II) complex, the reduction peak current decreased with a negative shift of the reduction peak potential and without the appearance of new peaks. The results showed that a new supramolecular complex was formed via interaction of the Phen-Zn(II) complex with dsDNA. The conditions of interaction and the electrochemical detection were carefully investigated. Under the optimum conditions, the decrease in the reduction peak current was directly proportional to the dsDNA concentration in the range of 0.4-18.0 mg L-1 with the linear regression equation: ?Ip?/nA = 349.48 + + 84.647(c/mg L-1) (n = 13, ? = 0.991) and a determination limit of 0.20 mg L-1 (3?). The relative standard deviation (RSD) for 10 parallel determinations of 10.0 mg L-1 dsDNA was found to be 2.03 %. The method was successfully applied to the detection of synthetic samples with satisfactory results.

Voltammetric study of the interaction between oxacillin sodium and cysteine in the presence and absence of Mn(II)ions in neutral buffer solution

In this study, the voltammetric behaviour of the interaction of oxacillin sodium (OXA) and OXA-cysteine (RSH) was studied by square-wave voltammetry, cyclic voltammetry in Britton-Robinson (B-R) buffer (pH 7.0). OXA gave two peaks at -0.248 and -1.224 V. For the interaction, the peak of mercurous cysteine thiolate (Hg2(SR)2) was selected. It was found that the peak currents corresponding to Hg2(SR)2 significantly decreased, while the peak potential shifted to more positive potentials upon the addition of OXA. The observed phenomena are due to the interaction of OXA with RSH on the surface of the mercury electrode. When OXA was added to the electrochemical cell along with Mn(II), new peaks at -0.146 and -0.608 V were observed. These peaks were due to the catalytic activity of OXA on the reduction of Mn(II) and could be attributed to the formation of Mn(II) complexes with different metal/ligand ratios. On the other hand, in the presence of RSH, the peak at -0.608 V vanished and a reduction peak was observed at -0.662 V. The catalytic reduction peak potential of Mn(II) at -0.662 V indicated that RSH slightly prevented the catalysis process of OXA due to their mutual interaction. .

The voltammetric determination of cobalt(II) in seawater – adsorptive preconcentration of the dimethylglyoxime complex

Conditions for the determination of trace Co in seawater are described. The method involves formation of the dimethylglyoxime complex and adsorptive accumulation onto a hanging mercury drop electrode at an applied potential of −0.70 or −0.96 V vs. SCE. The adsorbed complex is then reduced by scanning the electrode potential to −1.20 V; the reduction peak potential (Ep) is −1.12 V. Nickel behaves in a similar manner with Ep of −0.99 V but the Co complex appears to be preferentially adsorbed, making analysis for Co possible even in the presence of a large excess of Ni. Adsorption of organic matter also occurs; this does not affect analytical sensitivity but limits the maximum deposition time allowed in the analysis.Determination of Co in six seawater samples yielded results ranging from 4 to 114 ng L−1. Good agreement was obtained with the one reference sample (NASS-1) for which there was a certificate value. Keywords: cobalt, dimethylglyoxime, stripping voltammetry, adsorption, seawater.