Total X-ray Fluorescence Spectroscopy (TXRF)

Contact: World Agroforestry Centre (ICRAF), P.O. Box 30677-00100 Nairobi, Kenya. Tel: +254 020 722 4000. www.worldagroforestry.org

• 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.

• 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

• 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.

• 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.

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

Sample trays