Application of solidification of floating organic drop microextraction for inorganic anions: Determination of phosphate in water samples

•Solidification of floating organic drop microextraction for inorganic anions•Inexpensive, widely available UV–Vis detection technique•Determination of phosphate in real water samples

A novel dispersive liquid–liquid microextraction based on solidification of a floating organic drop (DLLME-SFO) for determination of orthophosphate was developed. The method includes the formation of molybdoantimonatophosphoric heteropoly blue (HPB) followed by a DLLME-SFO procedure and subsequent absorbance measurement using a micro volume cell (5 μL) with 10 mm path length. The final experimental conditions for HPB extraction were found to be: 0.6 mL of ethanol as dispersive solvent containing 55 μL of 1-undecanol as extraction solvent, magnetic stirring at 500 rpm, 10 min extraction time, decreasing the stirring rate to 150 rpm in order to group all the droplets and then solidification of the organic droplet in an ice bath for 5 min under continuous magnetic stirring. It should be pointed out that no centrifugation step is required. The calibration plot was linear in the range 4.0–60 × 10− 8 mol L− 1 of phosphate, with a correlation coefficient of 0.9982. The limit of detection (LOD), calculated as three times the standard deviation of the blank test (n = 10), was 7.4 × 10− 9 mol L− 1 of phosphate. The reported procedure was applied for determination of phosphate in real water samples.