Proposal of a controlled release of citrate by solubility equilibrium.

Some substances at high concentrations in both the body and the environment can be toxic. The remediation of contaminated environments, for example by metals in toxic concentrations is a fairly current problem. In this way, organic acids of low molecular weight, because they are biodegradable, constitute an alternative potentially for their use in phytoremediation processes. Among these acids, citric acid was chosen to be used in this work due to its suitable binder behaviour, with high stability constants. The purpose of this work was to develop a controlled release of citrate that allows its release to the soil solution to pre-defined concentrations by the system and that this concentration is maintained even if the binder is consumed in the complexation of metals, diluted or percolated. In this way, the system has an additional feature, compared to the conventional controlled release system. The presence of calcium citrate allowed for a slower release of citrate compared to citrate soluble salts or even with calcium citrate directly in solution. The Noyes-Whitney model allowed to explain the effects of pellet sizes and percentages of agar-agar. The pH of the receptor solution and the calcium concentrations used in the preparation of the gels influenced the equilibrium concentration of the citrate, demonstrating the independence of the controlled release process in relation to other variables in the solution. The controlled release system proposed in this work is a promising and very useful system for phytoextraction processes.

A new spectrophotometric method for determination of EDTA in water using its complex with Mn(III).

EDTA is an important ligand used in many industrial products as well as in agriculture, where it is employed to assist in phytoextraction procedures and the absorption of nutrients by plants. Due to its intensive use and recalcitrance, it is now considered an emerging pollutant in water, so there is great interest in techniques suitable for its monitoring. This work proposes a method based on formation of the Mn(III)-EDTA complex after oxidation of the Mn(II)-EDTA complex by PbO2 immobilized on cyanoacrylate spheres. A design of experiments (DOE) based on the Doehlert matrix was used to determine the optimum conditions of the method, and the influence of the variables was evaluated using a multiple linear regression (MLR) model. The optimized method presented a linear response in the range from 0.77 to 100.0µmolL(-1), with analytical sensitivity of 7.7×10(3)Lmol(-1), a coefficient of determination of 0.999, and a limit of detection of 0.23µmolL(-1). The method was applied using samples fortified at different concentration levels, and the recoveries achieved were between 97.0 and 104.9%.