Instrumental detection limits in TRXRF: cut-off and monochromatic excitation spectrum cases

Total Reflection X-ray Fluorescence (TRXRF) analysis has been widely used in several analytical applications in the last decade. Different instrumental settings, as well as the achieved levels of reproducibility, accuracy and detection limits have been reported. Two of the most widely spread configurations regarding to excitation radiation improvement procedures in analytical 'non-expensive' T R spectrometers are: using a so called 'Cut-Off' reflector, which allows to obtain a reflected beam with almost no high energy radiation and; using a monochromator device to obtain a reflected beam of monoenergetic and polarized radiation. This work compares the two mentioned settings for different monochromator devices in regard to the achieved instrumental detection limits. Several samples were analyzed to compare real detection limits. A multilayer structured mirror for soft X-rays (7-125 Angstroms), as well as different bent and flat crystals from Wave Length Dispersive X-ray Fluorescence Spectrometers were tested as monochromators. In addition previously obtained results using a C-W multilayer (d approx equal to 50 Angstroms) are presented for comparison. (author). 6 refs., 9 figs., 2 tabs