Liquid-Liquid Extraction, Separation, Preconcentration, and ICP-AES Determination of Lanthanum and Cerium with N-Phenyl-(1,2-methanofullerene C60)61-formohydroxamic Acid

A novel method for liquid-liquid extraction, separation, preconcentration, and simultaneous trace determination of cerium(IV) and lanthanum(III) with N-phenyl-(1,2-methanofullerene C₆₀)61-formohydroxamic acid (PMFFA) is reported. Lanthanum and cerium are extracted at pH 8.5 and 9.5, respectively in chloroform and recovered from monazite sands in the presence of thorium, uranium, and large number of cations and anions in high purity (99.98%). The extraction mechanism is investigated. The influence of PMFFA, pH, diverse ions, and temperature on the distribution constants of lanthanum and cerium was examined. The overall stability constants (log β₂K_e) and extraction constants (K_ex) for lanthanum(III) are 22.50 and 5.0 × 10^-9, respectively and for cerium(IV) are 21.51 and 3.9 × 10^-9, respectively. Lanthanum(III) gives a colourless complex with PMFFA which is extracted into chloroform having molar absorptivity 5.5 × 10⁴ L mol^-1 cm^-1 at 395 nm, and Beer's law 0.12-2.52 µg mL^-1, while cerium(IV) forms a red coloured complex, λ_max 460 nm, molar absorptivity 1.5 × 10⁴ L mol^-1 cm^-1, and Beer's law 0.46-9.26 µg mL^-1. For trace determination the extracts were directly inserted into the plasma for inductively coupled plasma atomic emission spectrometry ICP-AES measurements of lanthanum and cerium which increases the sensitivity 60 folds and obey Beer's law in the range, 2.1-37.5 ng mL^-1 for lanthanum and 9.2-186.4 ng mL^-1 for cerium. The method is applied for the determination of lanthanum and cerium in real and standard samples, sea water, and environmental samples.