Continuous flow configuration for total hydrocarbons index determination in soils by evaporative light scattering detection

A continuous flow configuration is proposed for the estimation of the hydrocarbon index in soils using for the first time evaporative light scattering detection (ELSD). The method is based on a membrane-enrichment of the hydrocarbons of interest (C10–C40), which are previously extracted from the soil matrix with a water:hexane mixture using a household microwave oven. The organic supernatant is cleaned-up through silica, evaporated and redissolved in a sodium dodecyl sulphate aqueous solution which is introduced in the loop of an injection valve. The sample, carried by an aqueous stream, passes through a continuous filtration unit fitted with a 1 μm pore size PTFE membrane, where the hydrocarbons are retained while the potential coextracted compounds are wasted. Quantitative elution of the C10–C40 fraction is accomplished by passing an acetone stream through the filter which drives the analytes to the ELSD system for analytical measurement. The detection limit was 1.8 μg ml−1, the linear range 5–25 μg ml−1 and the precision 4.3 %. The recoveries were between 93 and 97%. The proposed method was also evaluated by attenuated total reflexion-Fourier transform (ATR-FT-IR) analysis of the extracts.