Determination of metals in oil using total reflection X‐ray fluorescence spectrometry

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Abstract
Oil was chosen as a new sampl type for total reflection XRF. A thin‐film sample procedure is described which requires minimal sample preparation. This involves first bringing the oil into solution with a volatile solvent, then pipetting microliter amounts on to the reflector substrate followed by evaporation of the solvent. The linear dynamic range was found to extend to at least 5000 ppm. Detection limit measurements show that minute sample quantities are necessary for optimal detection limits of nanogram amounts. A maximum sample loading is required for the best detection limits in ppm. Using an Mo or Cu X‐ray tube, limits were found to be a few ppm or sub‐nanogram amounts. The spectrometer was calibrated by an internal standardization method and the results of determinations on sample solutions were typically within 10% relative accuracy.