Analytical capabilities of two-phase hollow-fiber liquid phase microextraction for trace multielement determination in aqueous samples by means of portable total reflection X-ray instrumentation

Liquid phase microextraction (LPME) procedures have been widely used in combination with atomic and emission spectroscopic techniques for the isolation and preconcentration of trace elements. However, its application in combination with total reflection X-ray spectrometry (TXRF) is still scarce. In this paper, we evaluate the possibilities and drawbacks of a two-phase hollow fiber LPME procedure in combination with TXRF for the simultaneous determination of trace amounts of Cr, Ni, Cu, Zn, Pb, and Cd in aqueous samples. After extraction of the analytes by using the optimum conditions (sample volume: 25 mL, complexing agent: APDC, organic solvent: hexylbenzene, extraction time: 2 h, extraction speed: 660 rpm), 10 mu L of the preconcentrated sample was deposited on a preheated quartz reflector, dried on a hot plate at 80 degrees C, and analyzed by TXRF. Using such conditions, limits of detection lower than 3 mu g L-1 were obtained for all metals. In spite of LODs improvement in comparison with the direct analysis of the aqueous samples (up to a factor of 100), precision of the results was not optimal (RSD similar to 20%). This fact may be related to the use of a low volatility solvent as extractant phase that hampers the later TXRF analysis.