DEVELOPMENT OF ENERGY-DISPERSIVE X-RAY-FL UORESCENCE SPECTROMETER WITH MONOCHROMATIC EXCITATION FOR THE DIRECT DETERMINATION OF TRACE-ELEMENTS IN ORGANIC MATRICES

An energy dispersive X-ray fluorescence spectrometer (EDXRF) with mono chromatic excitation has been developed for the direct determination o f trace elements in organic matrices. Monochromatization of X-rays by a crystal monochromator is effective in improving the signal to backgr ound ratio. Detection limits are less than 0.1 mu g g(-1) by monochrom atic excitation of Mo-K-alpha (17.4 keV) X-ray tube. But Ag, Cd and Sn can't be determined. The newly-constructed EDXRF with a combination o f three monochromatic excitations (9.7, 17.4 and 40 keV), can offer a higher sensitivity for the elements of atomic number larger than 22 (T i). At optimum conditions, detection limits of 0.02 similar to 0.34 mu g g(-1) (mean value, 0.13 mu g g(-1)) are ascertained for the 22 elem ents determined (Ti similar to Hg and Bi), and satisfactory precision (within 1% R.S.D.) is obtained. The proposed method is applied to the direct determination of trace elements in the NIST fuel oil (SRM 1634b ), and others. The results are in good agreement with the certified va lues.