Determination of trace amounts of manganese in water samples by flame atomic absorption spectrometry after dispersive liquid-liquid microextraction

Dispersive liquid-liquid microextraction was combined with flame atomic absorption spectrometry for the determination of manganese in water samples. 1-(2-Pyridylazo)-2-naphthol (PAN), chloroform and ethanol were used as chelating agent, extraction solvent and disperser solvent, respectively. In this extraction method, a mixture of 500 mu L ethanol (disperser solvent) and 100 mu L chloroform (extraction solvent) was rapidly injected by syringe into the water sample containing manganese ions and 4 x 10(-4) mol L-1 1-(2-pyridylazo)-2-naphthol (PAN) (chelating agent). Thereby, a cloudy solution was formed. After centrifugation (5 min at 4000 rpm), the droplets of the cloud were settled at the bottom of the conical test tube (70 +/- 2 mu L). The settled phase was separated using a micro-syringe and diluted to 100 mu l with ethanol. A microsample introduction system was employed for the nebulization of a micro-volume of the diluted solution into FAAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent, were optimized. Under the optimum conditions, an enrichment factor (EF) of 50 was obtained from only 5 mL of water sample. The calibration graph was linear in the range of 10-200 ng mL(-1) with limit of detection (LOD) of 3.0 ng mL(-1). The relative standard deviation (R.S.D.) for ten replicate measurements of 50 ng mL(-1) of manganese was 3.3 %. The method was successfully applied for the extraction and determination of manganese in some natural water samples.