Development of an analytical method to quantify EDTA and DTPA in real WTP effluents.

What is it about?

Our goal was to develop an affordable, rapid, green (no organic solvents) and robust analytical method that can be used to quantify these chelating agents in real WTP effluent. We also wanted to exploit the inherent capability of EDTA and DTPA to form complexes with metals for their quantification. To this end, we have previously demonstrated that size exclusion chromatography (SEC) coupled to a flame atomic absorption spectrometer (FAAS) can be used to observe the abstraction of Cd from humic acid (HA) by EDTA or DTPA (J. Environ. Sci. 57, 2017, 249-257). In brief, the injection of a HA-Cd complex on a SEC column using 10 mM Tris buffer pH 8.0 allowed to observe the intact HA-Cd complex, while the addition of increasing concentrations of EDTA or DTPA up to 20 micromolar resulted in a concentration dependent shift of the observed Cd peak to higher retention times. In this study we have obtained WTP effluents from three different WTP's in southern Alberta. After their filtration Tris was added to obtain 10 mM at pH 8.0 and the HA-Cd complex was injected. The retention time of the detected Cd peak shifted to larger retention times when increasing concentrations of equimolar EDTA and DTPA were added to each WTP effluent mobile phase (1, 2, 5, 7.5 and 10 micromolar). The results revealed correlation coefficients between 0.950-0.978 and demonstrate that the developed method can be used to detect EDTA and DTPA in real WTP effluents.

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Why is it important?

The developed method can now be applied to investigate the temporal release of EDTA/DTPA in WTP effluents. In particular this should allow one to identify when the concentration of these chelating agents peaks and what is the maximum concentration of chelating agents in WTP effluent when expressed as equimolar EDTA/DTPA.

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