Development of a spectrophotometric method for the determination of copper(II) ions using unsaturated amine ethers of the aromatic series

The complexation of copper(II) with two ligands (L), 2-methoxy-N-{(1S)-1-phenyl-2-[(prop-2-en-1-yl)oxy]ethyl}aniline (1, MENA) and 2-methoxy-N-{(1S)-1-phenyl-2-[(prop-2-yn-1-yl)oxy]ethyl}aniline (2, MINA), was studied. Organic solvents used for Cu(II) extraction can be ranked by extraction efficiency as follows: CHC3>CCl4>C2H4Cl2>C6H5Cl>C6H5CH3>C6H6>CH3COOC2H5>n-C4H9OH>iso-C5H11OH>C6H5CH2OH. After a single extraction with chloroform at a 4:1 aqueous-to-organic phase ratio, 97.5–98.3% of Cu(II) is extracted as a complex with the ligand. The optimal acidity range for the Cu(II)–MENA (1) and Cu(II)–MINA (2) complexes is pHopt 3.1–6.2 (pHform 1.2–8.7) and pHopt 3.3–7.4 (pHform 1.3–8.9), respectively. Phase volume ratios from 5:5 to 140:5 did not affect the extraction, allowing simultaneous concentration and extraction-photometric determination of Cu(II). A 28-fold increase in the volume of the aqueous phase relative to the organic phase does not affect the completeness of the extraction. A complex compound of Cu(II) ions with ligands 1 and 2 forms within 10 minutes, during which the absorbance increases from 0.395 to 0.460 and then stabilizes. The yield of the Cu(II) complex was maximal at a ligand concentration of CL=0.007 M and remained stable for at least 48 hours and more than two months after extraction. Cu(II)–L complexes 1 and 2 exhibit absorption maxima at 445 nm and 450 nm, respectively. The molar absorption coefficients are 445=4.21104 (for complex 1) and 450=4.37104 (for complex 2). The composition of the complexes corresponds to a 2:1 ligand-to-metal ratio. The Cu(II) complexes do not polymerize in chloroform (=1.13–1.17). Based on the results, a photometric method for the determination of copper in steel from various brands and in food processing has been proposed. This method is characterized by good reproducibility (relative standard deviation not exceeding 0.05) and a low limit of quantitation.