Combination of dispersive liquid–liquid microextraction with flame atomic absorption spectrometry using microsample introduction for determination of lead in water samples

Abstract

The dispersive liquid–liquid microextraction (DLLME) was combined with the flame atomic absorption spectrometry (FAAS) for determination of lead in the water samples. Diethyldithiophosphoric acid (DDTP), carbon tetrachloride and methanol were used as chelating agent, extraction solvent and disperser solvent, respectively. A new FAAS sample introduction system was employed for the microvolume nebulization of the non-flammable chlorinated organic extracts. Injection of 20 μL volumes of the organic extract into an air–acetylene flame provided very sensitive spike-like and reproducible signals. Some effective parameters on the microextraction and the complex formation were selected and optimized. These parameters include extraction and disperser solvent type as well as their volume, extraction time, salt effect, pH and amount of the chelating agent. Under the optimized conditions, the enrichment factor of 450 was obtained from a sample volume of 25.0 mL. The enhancement factor, calculated as the ratio of the slopes of the calibration graphs with and without preconcentration, which was about 1000. The calibration graph was linear in the range of 1–70 μg L −1 with a detection limit of 0.5 μg L −1. The relative standard deviation (R.S.D.) for seven replicate measurements of 5.0 and 50 μg L −1 of lead were 3.8 and 2.0%, respectively. The relative recoveries of lead in tap, well, river and seawater samples at the spiking level of 20 μg L −1 ranged from 93.8 to 106.2%. The characteristics of the proposed method were compared with those of the liquid–liquid extraction (LLE), cloud point extraction (CPE), on-line and off-line solid-phase extraction (SPE) as well as co-precipitation, based on bibliographic data. Operation simplicity, rapidity, low cost, high enrichment factor, good repeatability, and low consumption of the extraction solvent at a microliter level are the main advantages of the proposed method.