Analysis of chromium and copper by cathodic stripping voltammetry with mixed ligands

Cathodic adsorptive stripping voltammetry is one of the most sensitive analytical methods for ultratrace analysis. The detection limit is usually lower than 10⁻⁹ mol/L. Most adsorptive stripping procedures have been focused on the one ligand/one analyte approach. In order to reduce analysis time and sample volume, the possibility of simultaneously determining several metals by cathodic stripping voltammetry using a mixture of ligands was explored, e.g., by Colombo and van den Berg (1997). Here, we describe a new procedure for quantifying chromium and copper using 2,2′-bipyridine and 8-hydroxyquinoline (oxine). The effect of various operational parameters such as buffer type, ligand concentration, potential and time collection were assessed and optimized. Possible interferences by trace metals and organic matter were also investigated. Applicability for fresh water is illustrated. Electronic Publication     

The effect of the presence of trace metals on the oxidation of Sb(III) by hydrogen peroxide in aqueous solution

Despite its importance for understanding the behaviour of antimony in the environment, the oxidation kinetics of Sb(III) with natural oxidants is still not well understood. We have studied the oxidation of Sb(III) by hydrogen peroxide on a time scale of hours in the presence of some trace metals, Cu(II), Mn(II), Zn(II) and Pb(II), under pH and concentration conditions close to natural ones. The effects that these trace metals have on Sb(iii) oxidation by hydrogen peroxide vary. Zn(II) had no catalytic effect at all, but Cu(II), Mn(II) and Pb(II) did, though their effects were not uniform. Cu(II) significantly accelerated the reaction, which remained first-order with respect to Sb(III) at any Cu(II) concentration tested. Pb(II) and Mn(II) also enhanced the reaction rates, but the apparent order of the reaction with respect to Sb(III) changed to two. The trace metal effect observed was concentration dependent for Pb(II). The addition of the hydroxyl radical scavenger 2-propanol suggests that the trace metal catalytic effect observed involves the action of hydroxyl radicals, but that they are not responsible for the oxidation of Sb(III) by H2O2 in the absence of trace metals. The fact that Sb(III) can be oxidized by hydroxyl radicals present in water, even if it is not capable of producing them, has important environmental implications because hydroxyl radicals are known to be abundant in many natural waters such as seawater, humic-rich surface waters or rainwater.     

Helium isotopic constraints on simulated ocean circulations: implications for abyssal theories

There is ongoing controversy as to the dynamical significance of geothermal heat flow in shaping the abyssal circulation. In this paper, we gauge the impact of geothermal heating and vertical mixing parameterizations in the general circulation model OPA. The experiments are evaluated by comparing simulated mantle ³He with observations collected during the GEOSECS and WOCE programs. This tracer is particularly adapted to the validation of our numerical simulations because its injection into the ocean interior is tightly linked to geothermal processes. In agreement with previous studies, the model circulation is found very sensitive to the parameterization of the vertical mixing. The meridional overturning circulation (MOC) is globally intensified when moving from a constant mixing to a version with enhanced mixing near the ocean bottom, with the most drastic variation observed for AABW (+ 50%). Adding the geothermal heat flux mainly affects AABW circulation in the model, enhancing it all the more as the meridional circulation is slow (low vertical mixing), but proportionally less so when it is more vigorous (enhanced vertical mixing). This can be understood from the requirement of the abyssal ocean to maintain heat balance. The evaluation with mantle ³He simulations reveals that the version with low vertical mixing, with its sluggish circulation, produces unrealistically high a ³He isotopic composition. However, with a vertical mixing that is enhanced at depth, the ³He distribution falls within an acceptable range of values in the deep ocean. Finally, adding the geothermal heating to this enhanced mixing case provides a substantial improvement of the simulation of AABW in all basins but the Indian Ocean. ³He isotopic composition is then in good agreement with the observations. Taken jointly with observational estimates of the MOC intensity, these independent isotopic constraints suggest that both geothermal heating and enhanced diapycnal mixing at depth are key ingredients in the realistic simulation of abyssal circulation.