Determination of ultra traces of lead in water samples after combined solid-phase extraction-dispersive liquid-liquid microextraction by graphite furnace atomic absorption spectrometry

A solid-phase extraction coupled with dispersive liquid-liquid microextraction (DLLME) method followed by graphite furnace atomic absorption spectrometry (GFAAS) was developed for the extraction, preconcentration, and determination of ultra trace amounts of lead in water samples. Variables affecting the performance of both steps were thoroughly investigated. Under optimized conditions, 100 mL of lead solution were first concentrated using a solid phase sorbent. The extracts were collected in 1.50 mL of THF and 18 mu L of carbon tetrachloride was dissolved in the collecting solvent. Then 5.0 mL pure water was injected rapidly into the mixture of THF and carbon tetrachloride for DLLME, followed by GFAAS determination of lead. The analytical figures of merit of method developed were determined. With an enrichment factor of 1,800, a linear calibration of 3-60 ng L-1 and a limit of detection of 1.0 ng L-1 were obtained. The relative standard deviation for seven replicate measurements of 30 ng L-1 of lead was 5.2 %. The relative recoveries of lead in mineral, tap, well, and river water samples at spiking level of 10 and 20 ng L-1 are in the range 94-106 %.