Development of a simple hollow fibre supported liquid membrane extraction method to extract and preconcentrate dinitrophenols in environmental samples at ng L(-1) level by liquid chromatography

An easy and rapid hollow-fibre supported liquid membrane method (HFSLM) has been developed to extract and determinate the total concentration of four dinitrophenols in environmental water at ng L(-1) level. This extraction method provides a high selectivity, short extraction time and very low cost for real samples. It is a three-phase system, aqueous-organic-aqueous, where the organic solvent is held into the fibre pores, being in contact with the two other phases. The organic phase is formed by two different organic solvents, with two different polarities, n-undecane and toluene (1:1). The optimization step was performed using a three-variable Doehler design, involving three factors, stirring speed, fibre length and sample volume. The organic phase composition, as well as the pH of the acceptor and donor phases was also optimized. The extraction equilibrium was reached after 30 min, after which essentially the total amount (90-80%) of the four dinitrophenolic compounds were extracted from the sample. Better repeatability and reproducibility at the expense of lower enrichment factors was obtained compared with other methods, employing incomplete extraction during a fixed time. The matrix effect was tested by performing extractions from leachate water and river water. This method is linear in the range 0.1-100 microgL(-1) in different matrices, with detection limit around 100 ng L(-1), after extraction of 6 mL of sample and using high performance liquid chromatography for final analysis.