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.

IntroductionIntroduction

•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 - ApplicationsDetection 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 QuantificationAnalysis and Quantification

Sample types and preparationSample 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 PrincipleTXRF 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 TXRFKey advantages of TXRF

Sample trays