Reflectance FTIR spectroscopic analysis of metal complexation to EDTA and EDDS

Ethylenediaminetetraacetic acid (EDTA) is a common chelating ligand that is widely used in industry. EDTA, however, is not degradable in present wastewater treatment processes. (S,S)-Ethylenediaminedisuccinic acid (EDDS), an isomer of EDTA, is biodegradable and has recently received attention as an alternative metal chelating agent for this reason. Investigations reported here utilized reflectance FTIR spectroscopy for the analysis of metal complexation of EDTA and EDDS. The sampling techniques used were diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Similar studies using transmission mode FTIR have been carried out, but the analysis by reflectance techniques described here improved band resolution, minimized matrix interferences, and expanded on the previous work by providing an in situ method for analysis of pH dependence and metal complexation. Structural characteristics of sodium EDTA and EDDS compounds were identified using the results presented here. Complexes of Pb(II), Zn(II), Ni(II), and Cu(II) with EDTA and EDDS were identified by the frequencies of carboxyl group vibrational bands, the difference between asymmetric and symmetric carboxyl groups bands, the relative band intensities, and the band shifts as a result of changes in pH.