Energy‐dispersive x‐ray analysis of trace metals in micro amounts of aqueous samples by an ultra‐thin film droplet method

Abstract

When analyzing trace elements in an aqueous solution with a droplet method, the major part of the spectral background originates from the scattering of x-rays by the support film. The background is deliberately low when using an ultra-thin polyimide film (0.15 µm thick) as the sample support film. The incident x-rays generated by a micro focus x-ray tube (0.7 × 0.6 mm) pass through a pinhole and hit a small amount of sample on the support film. The incident x-ray beam energy is mostly used to excite the elements in the sample, resulting in the fluorescent spectra having a high peak-to-background ratio. This is because the excitation of elements in the sample by the scattered x-rays is avoided; the x-rays pass through the film without scattering. The polyimide film used in this method has the following characteristics. The small area (1.5 mm in diameter) in the central part of the support film is hydrophilic and the other part is hydrophobic in order to keep the sample solution inside the small part. The sample solution is dripped on to the hydrophilic part and then deposited in an area smaller than the x-ray beam diameter in a thermostated oven at 343 K. The matrix effect of the sample is negligible, because the analytical line intensity is approximately proportional to the mass of the analyte element. This paper describes (1) the method of handling small amounts of samples containing analyte elements at the level of a few nanograms, (2) the detection limits of several analyte elements and (3) an example of the quantitative analysis of trace metals in river water. Copyright © 1999 John Wiley & Sons, Ltd.