Automatic sequential injection liquid–liquid micro-extraction system for on-line flame atomic absorption spectrometric determination of trace metal in water samples

An automatic sequential injection (SI) liquid–liquid micro-extraction system incorporating a dual-conical micro-gravitational phase separator is proposed as versatile approach for on-line metal preconcentration and/or separation. Coupled to flame atomic absorption spectrometry (FAAS) the potentials of this novel schema are demonstrated for lead determination in water samples at the μg l−1 level. The non-charged lead complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into 300 μl isobutyl methyl ketone (IBMK) through the extraction coil. The organic phase containing the extracted metal complex is collected in the upper cavity of the phase separator and then forwarded to the nebulizer. All the critical parameters were optimized and offered good performance characteristics and high preconcentration ratios. A sample consumption of 10.5 ml enabled the determination of Pb(II) in the range of 3.0–250.0 μg l−1 with an enhancement factor of 120 and a sampling frequency of 25 h−1. The detection limit and the precision were 1.4 μg l−1 and 2.9% (at 50.0 μg l−1 concentration level), respectively. The proposed method was evaluated by analyzing certified reference material and was applied successfully to the analysis of natural water samples.