Determination of zinc in water samples by flame atomic absorption spectrometry after homogeneous liquid-liquid extraction

In this study, a new and simple homogeneous liquid-liquid extraction (HLLE) method based on a pH-independent phase-separation process was developed using a ternary solvent system [water-tetrabutylammonium ion (TBA ⁺)-chloroform] for the preconcentration of Zn²⁺ ions. A Schiff’s base ligand was used as the chelating agent prior to Zn²⁺ ions extraction. Flame atomic absorption spectrophotometry using acetylene-air flame was used for the quantification of analyte after preconcentration. The phase separation occurred due to ion-pair formation of TBA and perchlorate ion. The sedimented phase was then separated using a 100 μL micro-syringe and diluted to 1.0 mL with ethanol. The sample was introduced into the flame by conventional aspiration. After the optimization of complexation and extraction conditions such as pH 9.0, [ligand] = 1.0 × 10⁻⁵ M, [TBA⁺] = 2.0 × 10⁻² M, 100.0 μL of [CHCl₃] and [CLO₄⁻] = 2.0 × 10⁻² M, a preconcentration factor of 100 was achieved for only 10 mL of the sample. The relative standard deviation was 2.3% (n = 10). The limit of detection was sufficiently low and at ppb level. The proposed method was applied to the extraction and determination of Zn²⁺ in natural water samples with satisfactory results.