Spectrophotometric determination of trace amounts of lead(II) by ion-pair extraction with cryptand (2.2.2) and eosin

Authors:

• Walenty Szczepaniak,
• Bernard Juskowiak

Abstract

The solvent extraction of ion-pair complexes of calcium, strontium and lead (2.2.2) cryptates is described. The extraction equilibrium constants (D_C, K_ex and K_D) at room temperature are reported. The formation of the positively-charged lead cryptate ion and its extraction into chlorobenzene as an ion-pair with eosin are the basis of the proposed spectrophotometric determination of traces of lead. The high molar absorptivity of the ion-pair complex (ε{lunate} = 1.1 × 10⁵ l mol^-1 cm^-1) and the linearity of the calibration graph over the range 0-10^-5 M, allow even 0.1 ppm lead to be determined. The selectivity is high; there is no interference from cations often occurring with lead, such as Bi³⁺, Sn²⁺, Hg²⁺, Zn²⁺, Cd²⁺, Cu²⁺, Ca²⁺, Pd²⁺, Ag⁺ and Tl⁺. © 1982.