Chemical Speciation of Complexes of l-phenylalanine and maleic acid with toxic metal ions in Dimethylformamide -water Mixtures

The pH measurements of metal-ligand binary systems were carried out in aqueous media containing varying compositions of Dimethylformamide in the range of 0-50% (v/v) maintaining an ionic strength of 0.16 moldm^-3 with sodium nitrate at 303K by using a digital pH meter ELICO type readability of 0.01 (0-14). The electrode of the cell was calibrated with 0.05 moldm^-3 potassium hydrogen pthalate solution in the acidic region and with 0.01 moldm^-3 borax solution in the alkaline region to measure the response in the pH range. The effect of variations in asymmetry potential, liquid junction potential, activity coefficient, sodium ion error and dissolved carbon dioxide on the response of the glass electrode were accounted for in the form of correction factor [30,31]. Mechanical stirring of the solution was carried out by means of a magnetic stirrer. The pH metric titration assembly consisted of a double-walled spotless pyrex glass vessel of 100 mL capacity fitted with a Perspex lid through which the glass combination pH electrode and burette tip were admitted. Free acid titrations were performed before the metal -ligand titrations to calculate the correction factor. In each of the titrations, the titrand consisted of a mineral acid of approximately 1 mmol in a total volume of 50cm³. titrations with different ratios (1:0.25-1:0.50) of metal to ligand were performed with 0.4 moldm^-3 sodium hydroxide solution.