Energy dispersive x-ray fluorescence spectrometry with direct excitation at picogram levels

A Mo high-power X-ray tube with an optical point focus, followed by a thick Mo filter, irradiates a small and thin sample consisting of 50 ..mu..L of liquid deposited and evaporated on a 4 ..mu..m thick polypropylene film. The X-rays emitted by this sample are detected by a Si(Li) detector placed close to the sample. This arrangement allows one to reach, with a very convenient routine measurement, detection limits in the nanogram per milliliter range with total mass at picogram levels. Already hundreds of samples have been measured under these conditions. A more sophisticated sample preparation (thinner film, very good positioning of the sample, or more than 50 ..mu..L of solution) decreases the detection limits to picogram per milliliter levels, i.e., picogram of total mass. 16 references, 8 figures, 2 tables.