Sample preparation using plasma jet treatment for total reflection X-ray fluorescence analysis

Abstract

Total reflection X-ray fluorescence (TXRF) is widely used for trace element analysis. This method is advantageous because of its simple sample preparation. However, the sample must be placed within the analytical volume (region and height). In this study, the analytical volume was experimentally evaluated and visualized using thin, localized Au layers. The intensity distributions of the Au Lβ lines and background Au Lβ peaks were visualized. Images of the intensity ratio of the Au Lβ line and the background peak were drawn and analyzed to determine the analysis region on the glass substrate depending on the glancing angle. A glancing angle of 0.025° was optimal for TXRF analysis, resulting in a large signal-to-background (SB) ratio. Glancing angles of 0.05° and 0.075° were also effective for obtaining large SB ratios for a relatively large area (>4 mm²). To reduce the thickness of the dried residue and the self-absorption of the XRF emitted from the residue, a glass substrate was subjected to He plasma jet treatment. X-ray photoelectron spectroscopy confirmed that the carbon contamination was reduced from the surface of the glass by the plasma jet treatment, thereby modifying the chemical properties to confer hydrophilicity to the glass surface. The time variation of the C1 s peak intensity suggests that the hydrophilic property was maintained for several hours. The plasma-treated glass was effective in obtaining a thin layer-like residue from a white wine sample. The TXRF results indicated improved recovery and RSD, particularly for low-Z elements, because the absorption effect was reduced in the thin layer-like residue.