Fig. 9-1 Particle collection with impactor type air sampler The particles are directly collected by inertial impaction according to their size. The particle sizes are > 2.0 micrometer (top stage), 0.3 - 2.0 micrometer (middle stage), and 0.05 - 0.3 micrometer (bottom stage). The Si carriers for TXRF analysis are used as the collection plates.

Fig. 9-2 Schematic drawing of total-reflection X-ray fluorescence spectrometry (TXRF) Fluorescent X-rays are emitted from every element when irradiated by X-rays. Each element is identified by its X-ray energy, the amount of each element is determined by its X-ray intensity. By using an incident angle less than the critical angle, sensitive analysis becomes possible as a result of reduced background signals.

Fig. 9-3 TXRF spectra of size-fractionated aerosol particles The amounts of elements can be calculated by comparing the peak intensities of elements with that of the internal standard (Se). In addition, the dependence of the elemental composition on particle size can be investigated by analyzing the size-fractionated particles.

Aerosol particles are composed of various elements. The particles often contain harmful heavy metals that can adversely affect the human body. In particular, particles less than a few micrometer in aerodynamic diameter are important because they can penetrate the gas-exchange tract of the alveoli. Therefore, the determination of the elemental composition of aerosol particles is of great importance to estimate health effects. In addition, the elemental composition gives valuable information on the origin of the particles. In this case, a simple, rapid, and sensitive analytical technique is required because particles continually change in size and elemental composition. We have developed a method to measure the elemental composition of particles using the combination of direct particle collection by impaction and analysis with total-reflection X-ray fluorescence (TXRF) spectrometry. The principle of the particle collection is shown in Fig. 9-1. The impactor is equipped with three impactor stages and the size-fractionated particles are collected on the collection plates. Here, we used sample carriers for TXRF as the impaction plates. In the TXRF analysis (Fig. 9-2), we modified the sample holders to use carriers with diameters of 25 mm. Silicon (Si) was used as the carrier material to provide a sensitive analysis. Fig. 9-3 shows the TXRF spectra of aerosol particles collected on the Si carriers for 48 hours. In the analysis, we use Se as an internal standard for quantification. As a consequence, elements with concentrations of pg levels could be measured. We found that Pb and Zn, which originate from anthropogenic sources, are mainly concentrated in fine particles. In contrast, the elements Ca, Ti, and Fe, which originate from geo-genic sources such as soil, are concentrated in coarse particles. This method is now applied on trial to the analysis of trace amounts of nuclear materials emitted from nuclear facilities.

Reference F. Esaka et al., The Use of Si Carriers for Aerosol Particle Collection and Subsequent Elemental Analysis by Total Reflection X-ray Fluorescence Spectrometry, Spectrochim. Acta B, 58(12), 2145 (2003).

Select a topic in left column

Persistent Quest Research Activities 2003 Copyright (C) Japan Atomic Energy Research Institute