Electrochemical tuning of capacitive response of graphene oxide.

The increasing energy demands of modern society require a deep understanding of the properties of energy storage materials, as well as the tuning of their performance. We show that the capacitance of graphene oxide (GO) can be precisely tuned using a simple electrochemical reduction route. In situ resistance measurements, in combination with cyclic voltammetry measurements and Raman spectroscopy, have shown that upon reduction GO is irreversibly deoxygenated, which is further accompanied by structural ordering and an increase in electrical conductivity. The capacitance is maximized when the concentration of oxygen functional groups is properly balanced with the conductivity. Any further reduction and deoxygenation leads to a gradual loss of capacitance. The observed trend is independent of the preparation route and the exact chemical and structural properties of GO. It is proposed that an improvement in the capacitive properties of any GO can be achieved by optimization of its reduction conditions.

In vitro fluoride release from a different kind of conventional and resin modified glass-ionomer cements.

Fluoride release is important characteristic of glass-ionomer cements. Quantity of fluoride ions released from the glass-ionomer cements has major importance in definition of their biological activity. The objectives of this study were to define the quantity of fluoride ions released from the experimental glass-ionomer cements and to define the effect of fluoride ions released from the experimental glass-ionomer cements on their cytotoxicity. Concentrations of the fluoride ions released in the evaluated glass-ionomer cements were measured indirectly, by the fluoride-selective WTW, F500 electrode potential, combined with reference R503/D electrode. Statistical analyses of F-ion concentrations released by all glass-ionomers evaluated at two time points, after 8 and after 24 hours, show statistically higher fluoride releases from RMGICs: Vitrebond, Fuji II LC and Fuji Plus, when compared to conventional glass-ionomer cements: Fuji Triage, Fuji IX GP Fast and Ketac Silver, both after 8 and after 24 hours. Correlation coefficient between concentrations of fluoride ion released by evaluated glass-ionomer cements and cytotoxic response of UMR-106 osteoblast cell-line are relatively high, but do not reach levels of biological significance. Correlation between concentrations of fluoride ion released and cytotoxic response of NIH3T3 mouse fibroblast cell line after 8 hours is high, positive and statistically significant for conventional GICs, Fuji Triage and Fuji IX GP Fast, and RMGIC, Fuji II LC. Statistically significant Correlation coefficient between concentrations of fluoride ion released and cytotoxic response of NIH3T3 cell line after 24 hours is defined for RMGIC Fuji II LC only.

Rapid chromatographic methods for the identification and determination of chlorophenoxy herbicides.

Derivatives of chlorophenoxy carboxylic acids have been the first class of herbicides in continuous use since 1947. The main interest for these substances is due to their evident chronic toxicity and carcinogenic effect. On the other hand, they can cause acute toxicity and have significant role in suicidal attempts. In this paper we have investigated analytical approaches that could be used for rapid identification and determination of chlorophenoxy herbicides in modestly equipped laboratories for the clinical toxicology. Thin layer chromatography on cellulose layer using neutral red as ion pairing reagent gave the best results in separation of different herbicides, making possible visualisation at the daylight without further reagents or equipment. High performance liquid chromatography (HPLC) methods for separation on C8 and C18 phases with and without ion-pairing reagent were compared. It was found that HPLC on C18 phase utilising ion-suppression mode has the best reproducibility, linearity and mass limit of detection suitable for quantification of chlorophenoxy herbicides after acute poisoning.