Cloud-point extraction of selected polycyclic aromatic hydrocarbons by nonionic surfactants

Effect of nonionic surfactants on the performance of the cloud-point extraction (CPE) processes in preconcentrating trace amount of polycyclic aromatic hydrocarbons (PAHs), consisting of two to five fused rings, from aqueous solution at 25 °C was studied. Three biodegradable nonionic surfactants with molecular similarity were employed. Cloud-point temperatures (CPTs) of these micellar solutions were regulated and reduced enough with addition of sodium sulfate and sodium phosphate, so that the CPE process could be facilitated at 25 °C. Furthermore, quadratic equations in additive concentration are found to fit the CPTs of these micellar solutions well. It is observed that the preconcentration factor could be enhanced either by increasing the salt concentration or by decreasing the initial surfactant concentration present in the micellar solution. With CPTs regulated at around 15 and 18 °C with addition of Na2SO4 and Na3PO4, preconcentration factors in between 30 and 45 obtained from 1 wt% micellar solutions of these three surfactants appear in the order of Tergitol 15-S-9 > Neodol 25-7 > Tergitol 15-S-7, coincidently with the hydrophilicity order of surfactants. The average preconcentration factor was empirically fitted well as a simple power-law function of surfactant concentration used in the CPE process. The obtained empirical power-law indices are close to negative unity.