Supervanadophile: Complexation, preconcentration and transport studies of vanadium by octa functionalized calix[4]resorcinarene-hydroxamic acid

A new octa functionalized calix4]resorcinarene bearing eight hydroxamic acid groups (OFCHA) has been synthesized and its analytical properties have been investigated. To elucidate the structure of the compound, elemental analysis, FT-IR and ¹H NMR spectral data have been used. The compound showed high affinity and selectivity for vanadium(V) in presence of large quantities of associated metal ions. The complexation of vanadium(V) with OFCHA has a 4:1 metal: ligand stoichiometry as evaluated by Job’s plot. A spectrophotometric method is proposed for the extractive determination of vanadium(V) in an acidic medium in the presence of diversified matrix, and verified by ICP-AES. Under the optimum condition of acidity, solvent, interfering ions and OFCHA concentration, the molar absorptivity of the complex is 5630 l mol^-1 cm^-1 at 495 nm. The system obeys Beer’s law over the range 0.125–8.75 μg ml^-1 of vanadium(V) with Sandell sensitivity 0.009 μg cm^-2. The preconcentration factor and overall stability constant evaluated at 25 °C were 142 and 14.18, respectively. The complexation is characterized by favorable enthalpy and entropy changes. Liquid membrane transport studies of vanadium(V) were carried out from source to the receiving phase under controlled conditions and a mechanism for transport is suggested. To check the validity of the proposed method, vanadium is determined in environmental, biological samples and some standard reference materials from NIST and BCS.