XRF, X-ray Fluorescence Spectroscopy

Introduction to X-ray Fluorescence Spectroscopy (XRF) 

XRF spectroscopy Analysis Labs: X-ray fluorescence spectroscopy (XRF) is a robust, non-destructive analytical technique utilized to determine the chemical composition of a wide variety of samples including liquids, solids, slurries and loose powders. The technique works by using an X-ray tube to excite electrons in the sample, which then emit secondary X-rays (fluorescence) with discrete energies characteristic of the elements present in the sample. Another use of XRF is determination of the thickness and composition of layers and coatings. XRF technique can analyze elements from beryllium (Be) to uranium (U) in concentrations ranging from 100 wt% to sub-ppm levels. XRF is a high precision, accurate analytical technique that can be used both for qualitative and quantitative analysis in testing laboratories.

The XRF technology provide elemental analysis of a huge variety of materials including polymers, metals, alloys, ceramics, geological materials, petroleum products, soil, and paints. XRF is one of the most straightforward and convenient ways to perform elemental analysis. XRF is used for a vast number of industrial, research and educational applications. Through XRF technique, the derived data can be used to obtain qualitative, semi-quantitative and quantitative information about the major, minor and even trace elements in a specimen.

Figure: Interaction of X-rays with a substance

Figure: Principle of Fluorescent X-rays Emission

Principle and Methodology of X-ray Fluorescence Spectroscopy (XRF) 

The principle behind XRF is based on the atomic emission method. When an atom is bombarded with high energy X-rays, it emits secondary X-rays that are characteristic of the element present. XRF technique measures wavelength and intensity of ‘light’ (X-rays in this case) emitted by energized atoms in the specimen. The energy of the emitted X-rays is proportional to the atomic number of the element and can be used to identify and quantify its presence in a sample. The intensity of the emitted X-rays is proportional to its concentration in the sample and can be used for quantitative analysis.

XRF spectrometers or XRF analyzers are used for elemental and thin film analysis. XRF instruments typically consist of an X-ray tube with an associated power supply; a detector; data acquisition electronics; a computer system for data analysis; and software for data processing and interpretation. The instrument must also have appropriate shielding against radiation leakage from the source material being analyzed. The spectrometers range from  wavelength-dispersive high-performance XRF (WDXRF) systems to energy-dispersive benchtop XRF (EDXRF) systems. 

Uses of X-ray Fluorescence Spectroscopy (XRF)

XRF is widely used for many applications including environmental monitoring, industrial process control, quality control in manufacturing industries, geochemical exploration for minerals, archaeological research, food safety testing, forensic analysis, and more. It has become an invaluable tool for scientists in many fields due to its versatility and accuracy.

Advantages of X-ray Fluorescence Spectroscopy (XRF)

XRF has several advantages over other analytical techniques such as atomic absorption spectroscopy or inductively coupled plasma mass spectrometry (ICPMS). It has a dynamic range, where it can measure both low and high concentrations of elements with good accuracy. XRF technique can be readily automated in testing labs for use in high-throughput industrial environments. XRF technique also has good sensitivity, allowing it to detect trace elements at concentrations as low as parts per billion. Additionally, sample preparation is straightforward and fast, allowing testing to be performed quickly and easily on solid, liquid, or gaseous samples.

Applications

X-Ray fluorescence is used in a wide range of applications, including

• research in igneous, sedimentary, and metamorphic petrology
• soil surveys
• mining (e.g., measuring the grade of ore)
• cement production
• ceramic and glass manufacturing
• metallurgy (e.g., quality control)
• environmental studies (e.g., analyses of particulate matter on air filters)
• petroleum industry (e.g., sulfur content of crude oils and petroleum products)
• field analysis in geological and environmental studies (using portable, hand-held XRF spectrometers)

X-Ray fluorescence is particularly well-suited for investigations that involve

• bulk chemical analyses of major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) in rock and sediment
• bulk chemical analyses of trace elements (in abundances >1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, Zn) in rock and sediment – detection limits for trace elements are typically on the order of a few parts per million

X-ray fluorescence is limited to analysis of

• relatively large samples, typically > 1 gram
• materials that can be prepared in powder form and effectively homogenized
• materials for which compositionally similar, well-characterized standards are available