Liquid-phase microextraction as an attractive tool for multielement trace analysis in combination with X-ray fluorescence spectrometry: an example of simultaneous determination of Fe, Co, Zn, Ga, Se and Pb in water samples

In recent years, liquid-phase microextraction (LPME) has become one of the most valuable techniques for the preconcentration and separation of trace and ultratrace elements. LPME can be combined with an atomic technique which requires only a few microlitres of liquid to perform a measurement, e. g. electrothermal atomic absorption spectrometry. In this study, combining LPME with X-ray fluorescence spectrometry (XRF), a dried-spot technique is proposed. Since the X-ray beam can be focused on a small spot size and simultaneously LPME produces a very small drop of a volume ranging from 2 to 30 mu L, the combination of these two techniques is a very promising tool for multielement trace and ultratrace analyses. The present research was performed using dispersive liquid-liquid microextraction (DLLME) with APDC as a chelating agent. Nevertheless, any LPME technique, e. g. single-drop microextraction (SDME), can be applied in combination with XRF. Because XRF measurement follows the microextraction, deposition and drying of the small drop, the influence of the diameter of the dried residue on the intensity of fluorescent radiation is discussed in detail. Pipetting and spray-on techniques are proposed for the deposition of the small drop onto the substrate (membrane filter or Mylar foil). Under the optimized conditions, the detection limits were 2.8, 1.6, 2.5, 1.7, 2.1 and 4.1 ng mL(-1) for Fe, Co, Zn, Ga, Se and Pb, respectively, with a preconcentration factor of 250 for 5 mL of the water sample.