Total X-ray Fluorescence Spectroscopy (TXRF) Contact: World Agroforestry Centre (ICRAF), P.O. Box Nairobi, Kenya. Tel: TXRF is a versatile analytical technique for determining elemental content in liquids, solids and loose powders. The main principle is that atoms, when irradiated with X-rays, radiate secondary X-rays – the fluorescence radiation. Each element is associated with a specific wavelength and energy of the fluorescence radiation. The concentration of each element is calculated using the fluorescence intensity. TXRF combines high accuracy and precision with simple and fast sample preparation for the analysis of elements from Sodium (Na; 11) to Uranium (U; 92) in concentration ranges from 100% to sub-ppm level. TXRF is a powerful diagnostic tool for agriculture and environment. TXRF analysis is suitable for all types of samples Sample digestion is not normally required. Samples are prepared on a sample tray that reflects X-ray radiation. Trays have a diameter of 30 mm, made of acrylic or quartz glass. Liquids are prepared directly on the sample tray. Several μl are transferred to the glass disc using a pipette and evaporated (Figure 2). Powdered samples are finely ground (<50 μm), prepared in suspensions and transferred to the sample tray. Powder samples (a few μg of sample) can also be transferred directly, using a Q-tip, for semi-quantitative analysis. Introduction Typical Lower Limits of Detection (LLD) are presented in Figure 5. The LLD for many elements is 1-10 μg/l. Elements from Na (11) to U (92) are detected Applications include: Plant trace element diagnostics Soil element fingerprinting Soil heavy metal screening Soil solution/extract analysis Water quality analysis Detection limits - Applications All elements from Sodium to Uranium (excl. Niobium, Molybdenum and Technetium) can be analyzed (Figure 1). TXRF analysis is based on internal standardization; an element, which is not present in the sample, must be added for quantification purposes (Figure 4). Measurement of the complete spectrum; all detectable elements are measured simultaneously. Analysis and Quantification Sample types and preparation The working principle of TXRF spectroscopy as realized in the S2 PICOFOX spectrometer is shown in Figure 3. A primary beam generated by a X-ray tube is monochromatized by Bragg-reflection on a Ni/C multilayer. Monochromatized X-rays hit a polished sample carrier (quartz glass or acrylic glass) at a very shallow angle of incidence. X-rays are totally reflected by the surface of the sample carrier at a very small angle (0.3 – 0.6 °). Fluorescence radiation is emitted only by the sample deposited on the carrier surface. The characteristic fluorescence radiation emitted by the sample is detected by an energy-dispersive detector. Intensity is measured by means of an amplifier coupled to a multichannel analyzer. TXRF Working Principle Fig. 1: Elements analyzed; Na (11) to U (92) Fig. 4: Typical spectrum showing peaks of several elements Fig. 3: Schematic working principle of the S2 PICOFOX spectrometer Fig.2: Sample preparation steps for the TXRF analysis of liquids S2 PICOFOX TXRF spectrometer Fig. 5. Lower Limits of Detection Fast and simple sample preparation; no need for pressed pellets Simultaneous multi-element trace analysis without external calibration Analysis of small sample amounts in nanogram or microgram range Suitable for various sample types: solids, powders, liquids, suspensions Portable system for fast in-field analyses; low power rating Low maintenance and operating cost Highly reproducible Low limits of detection Key advantages of TXRF Sample trays