Ultrasound assisted cold-induced aggregation: an improved method for trace determination of volatile phenol

We report on a simple, rapid and efficient extraction procedure, referred to as ultrasound-assisted cold-induced aggregation (USA-CIAME), for the extraction of phenol from aqueous samples. In this method, very small amounts of the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate (the extractant) are dissolved in a sample solution containing phenol and ultrasonicated for 1 min. The solution is cooled in an ice bath upon which a cloudy solution forms. Following centrifugation, the extractant phase settles at the bottom of a conical-bottom centrifuge tube. Phenol is photometrically determined after its chromogenic reaction with 4-aminoantipyrine in the presences of hexacyanoferrate at pH 10.0. Compared to the conventional cold-induced aggregation microextraction (CIAME) and dispersive liquid liquid microextraction (DLLME), the optimized approach displays the highest extraction efficiency at room temperature, and the shortest extraction time (5 min). Key parameters affecting the performance were evaluated and optimized. Under optimum conditions, the limit of detection of phenol is 0.86 μg L−1, and the enrichment factor is 75. The calibration graph as linear over the range from 3 to 150 μg L−1, and the relative standard deviation is 2.65% (n = 5). The method was successfully applied to the determination of phenol in water samples.