Mixed micelle-mediated extraction of alizarin red S complexes of Zr(iv) and Hf(iv) ions prior to their determination by inductively coupled plasma-optical emission spectrometry

Abstract

A modified cloud-point extraction method using a mixed surfactant has been developed for the preconcentration of Zr(IV) and Hf(IV) prior to their determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). The method is based on the complexation of Zr(IV) or Hf(IV) with Alizarine Red S (ARS) at pH 2.5 in the presence of cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and non-ionic surfactant Triton X-114. Phase separation was accomplished at room temperature in the presence of 0.1 mol L⁻¹ sodium sulphate. The surfactant-rich phase containing Zr(IV) or Hf(IV) was separated then diluted with methanol/concentrated nitric acid mixed solvent (5 : 1) before its introduction into ICP-OES for the determination. The optimal extraction and reaction conditions were evaluated and optimized. Under the optimized conditions, the calibration graphs were linear in the range of 0.5–1000 and 0.5–850 ng mL⁻¹ with detection limits of 0.18 and 0.25 ng mL⁻¹ for Zr(IV) and Hf(IV), respectively. The RSD values for five replicates of Zr(IV) and Hf(IV) at 50 ng mL⁻¹ concentrations were 2.1 and 2.3%, respectively, and the enrichment factors for 100 mL samples were obtained as 120 and 105 for Zr(IV) and Hf(IV), respectively. The accuracy of the results was verified by analyzing the spiked water from different sources and synthetic mixtures. The proposed method has been applied for the determination of Zr(IV) and Hf(IV) in some real samples such as clay, rocks and silver alloy samples with satisfactory results.