On-Site Turbidimetry for Oils in Soil Using Co-Nonsolvency of Poly(N-isopropylacrylamide) in Water – Ethanol Binary Solvent

Abstract

Poly(N-isopropylacrylamide), PNIPAAm, is quite soluble in water and alcohol, but insoluble in certain mixtures of them. This property, called co-nonsolvency, was applied to the extraction of oils from ethanol eluate and turbidimetric detection. Oils were eluted with a PNIPAAm – ethanol solution by passing through the soil sample. Subsequently the oils were extracted into a dispersed polymer phase, forming from the eluate with the addition of an aqueous NaCl solution. The polymer phase adherent on the wall of a polypropylene bottle was separated from the liquid phase, and dissolved into freshly added water. The oils in the polymer phase were deflocculated as an emulsion particulate in the water. The turbidity of the emulsion was dependent on amounts of the oils. A column-type eluting apparatus equipped with a filter, a bottle for the reaction, and a portable photometer were proposed as a kit for on-site analysis. Oils at 400 – 5000 mg kg⁻¹ in 1.0 g of soil could be determined within about 10 min of the entire procedure. The results from simulated polluted samples were successfully related linearly to the value of the total petroleum hydrocarbon (TPH) measured by GC. The proposed method is a useful screening tool for judging soil pollution with mineral oil.