Ultra trace characterization of small droplets with x-ray fluorescence analysis using x-ray microbeam

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X-ray fluorescence analysis was carried out using an x-ray microprobe system dedicated in the BL37XU of the SPring-8. A thin film of Cu evaporated 1.2 nm onto the Kapton substrate was utilized for evaluating the minimum detection limits. By employing the optimized detection geometry the detection limits of 50 ag (or Cu atoms of 5 × 10^5) was achieved. The obtained detection limits is one of the lowest values reported in the worldTo generate micro droplets a droplet-generator was utilized which is driven by the piezo actuators. Liquid droplets were titrated onto the thin films of polypropylene, and the droplets fixed with the vapor of the cyanoacrylate or the residue of the dried droplets were examined. A combination of the droplet-generator and the automated XY stage has enabled us to generate a small droplet down to 30 pL onto the designed position. However surface characteristics of the substrate strongly affects the resultant position and the residue of,the droplets. A hydrophilic surface widen the size of the residue, and the hydrophobic surface often change the position of the residue from the initial position