Definition
X-ray fluorescence spectrometer is an instrument for elemental analysis based on X-ray fluorescence effects. When a sample is irradiated with high-energy X-rays, its inner electrons are excited and detached from the atoms, and then the outer electrons transition to the inner vacancy and release characteristic X-ray fluorescence. By detecting the energy or wavelength of these characteristic X-rays, the elements in the sample can be analyzed qualitatively and quantitatively. This technology has the characteristics of non-destructiveness, simultaneous detection of multiple elements, and fast analysis speed, and is suitable for various forms of samples such as solids, powders, and liquids.
Principle
The working principle of X-ray fluorescence spectroscopy is based on the excitation and deexcitation process of electrons in the inner layer of atoms. When the energy of the incident X-ray photons is higher than the binding energy of the electrons in the inner layer of the sample atom, the electrons are knocked out to form holes. Subsequently, electrons at higher energy levels transition to the hole and release energy in the form of characteristic X-ray photons. Different elements have different atomic structures, and the characteristic X-ray energy released by them is specific, so the element species can be determined by measuring the energy or wavelength of the characteristic X-rays. Quantitative analysis is based on the correlation between the intensity of characteristic X-rays and the concentration of elements, usually calculated by calibration curves or basic parameter methods.
The relationship between the energy E of characteristic X-rays and the atomic number Z can be described by Mosselle's law:
√(ν/R) = a(Z - b)
where ν is the characteristic X-ray frequency, R is the Rydberg constant, and a and b are constants. This formula reveals the linear relationship between the square root of the X-ray frequency and the atomic number of elemental characteristics, which is the basis for the qualitative analysis of X-ray fluorescence.
Measurement method
The measurement methods of X-ray fluorescence spectrometer are mainly divided into two types: wavelength dispersion type and energy dispersion type. Wavelength dispersive spectrometers disperse characteristic X-rays through spectroscopic crystals, and use detectors to measure the intensity of X-rays at specific wavelengths at different diffraction angles. The method has high resolution and is suitable for light element analysis and complex matrix samples. Energy dispersive spectrometers directly use semiconductor detectors to measure the energy distribution of characteristic X-rays, without the need for a spectroscopy system, and have a relatively compact structure that enables rapid multi-element analysis.
In terms of sample preparation, solid samples usually need to be polished and flattened, powder samples can be pressed or melted to make samples, and liquid samples can be placed directly in special sample cups. During the measurement process, appropriate parameters such as tube voltage, tube current, and measurement time should be set according to the sample type, and corresponding calibration methods, such as empirical coefficient method or basic parameter method, should be selected to reduce the impact of matrix effects.
Influencing factors
The results of X-ray fluorescence spectroscopy are influenced by a variety of factors. Sample matrix effects are one of the main influencing factors, including absorption enhancement and particle size effects, which can cause deviations between the measured intensity and the true concentration. Sample uniformity and surface flatness also affect the excitation and detection efficiency of X-rays. Instrumental factors such as the stability of the X-ray tube, the resolution of the detector, and the linear range of the count rate may play a role in the measurement accuracy. Environmental conditions such as temperature fluctuations can cause instrument drift. In addition, line overlap interference, especially the characteristic peak overlap of adjacent elements, can pose challenges for qualitative and quantitative analysis. With proper sample preparation, instrument calibration, and data processing methods, these effects can be controlled to some extent.
Application
X-ray fluorescence spectrometers have a wide range of applications in several fields. In materials science, it can be used for compositional analysis of materials such as metal alloys, ceramics, glass, etc. The field of geology and minerals is often used for the elemental census of ores, soils and sediments. In terms of environmental monitoring, it is suitable for the detection of harmful elements in atmospheric particulate matter and solid waste. In industrial production, it is used for metallurgical process control, cement composition analysis, and RoHS compliance screening of electronic products. Additionally, in fields such as archaeology and art identification, its non-destructive nature makes it an effective tool for material composition analysis. Different application scenarios have different requirements for the detection limit, accuracy, and element range of the instrument, and the appropriate configuration needs to be selected according to the specific needs.
Selection
When choosing an X-ray fluorescence spectrometer, there are many aspects to consider. Analytical needs are the primary factor, including the range of elements to be measured, detection limit requirements, sample type, and throughput. For light element analysis, wavelength dispersive spectrometers often have an advantage; For rapid multi-element screening, the energy dispersive type may be more suitable. In terms of instrument performance, it is necessary to pay attention to indicators such as resolution, stability, and long-term repeatability. Operational complexity is also a consideration, as it relates to sample preparation processes, software ease of use, and maintenance requirements. In addition, the space conditions, power requirements and safety measures of the laboratory should be considered. It is recommended to conduct sample measurements before selection, evaluate the performance of the instrument in practical applications, and make comprehensive decisions based on factors such as technical support and after-sales service.