An ATR−FTIR Study of Glyphosate and Its Fe(III) Complex in Aqueous Solution

An ATR−FTIR study of the vibrational spectrum of glyphosate (N-phosphonomethylglycine) in aqueous solution 1 M in NaCl is reported. Band assignments are given in the 1800−850 cm-1 range based on the analysis of the spectral changes from low to high pH values (2−11). Potentiometric titrations of glyphosate are performed at 0.1, 0.5, and 1 M ionic strengths in NaCl and the pKa2, pKa3, and pKa4 values determined. A chemometric analysis of the spectral data has been carried out to support the assignments and reproduce the pKa values. In addition, the ATR−FTIR spectrum of the 1:1 Fe(III)/glyphosate complex in aqueous solution is analyzed by comparison with that of the free ligand.