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The core technology and detection principle of ROHS instruments: in-depth interpretation of X-ray fluorescence spectroscopy (XRF)
Date: 2025-11-17Read: 0
Most ROHS instruments are based on X-ray fluorescence spectroscopy (XRF) technology to detect harmful substances. The core of their principle and technology lies in the precise identification of element composition and content in materials through the process of "excitation emission analysis".
The basic principle of XRF technology is that when high-energy X-rays (generated by the X-ray tube or radioactive isotope source inside the instrument) are irradiated onto the surface of the sample, the inner layer electrons (such as K layer and L layer) of the atoms in the sample will be ejected, forming holes. At this point, the outer electrons (such as the L layer and M layer) will transition to the inner layer to fill the holes, while releasing characteristic X-rays with specific energy (i.e. fluorescent X-rays). The characteristic X-ray energy of each element is unique (such as the K α line of lead, which is about 72.8 keV, and the K α line of cadmium, which is about 23.1 keV). By detecting the energy and intensity of these fluorescence, it is possible to determine which elements are present in the sample and their relative content.
ROHS InstrumentKey technology implementation:
Excitation source: Mainstream equipment uses X-ray tubes (such as rhodium targets and tungsten targets) to generate primary X-rays of different energies by adjusting the tube voltage (usually 5-50kV) and current (1-100mA) to meet the excitation requirements of light elements (such as sodium and magnesium) and heavy elements (such as lead and mercury). Some portable devices use radioactive isotope sources (such as silver-109 and cadmium 109), but their energy is fixed and their flexibility is low.
Detector: divided into proportional counter (for light elements) and silicon drift detector (SDD)/semiconductor detector (for heavy elements). SDD is currently a standard configuration for high-end instruments, with the characteristics of high resolution (distinguishing adjacent elements with an energy difference of only 0.1 keV) and fast response speed (suitable for short-term detection), which can accurately identify elements with extremely low limits such as lead, cadmium, mercury, etc.
Data analysis system: The built-in software of the instrument will convert the fluorescence signal received by the detector into an energy intensity spectrum, match the characteristic peak positions of known elements through algorithms (such as the K α peak of lead at 72.8keV), and calculate the specific content based on the standard curve (such as ppm level accuracy).
Advantages and limitations of XRF technology: The major advantages of XRF technology are non-destructive (no need for sample dissolution or destruction), fast (single detection only takes tens of seconds to minutes), and multi-element synchronous analysis (can simultaneously detect dozens of elements). But its limitations lie in its insensitivity to ultra light elements such as hydrogen and helium, and for samples with thicker surface coatings (such as painted metals), surface interference needs to be removed by polishing.
Understanding the principles and instrument implementation of XRF technology can help users choose suitable ROHS instruments based on their detection needs (such as element range and accuracy requirements), and fully utilize their detection efficiency through standardized operation.