ASTM F2617-15 Standard Test Method for Identification and Quantification of Chromium, Bromine, Cadmium, Mercury, and Lead in Polymeric Materials Using Energy Dispersive X-Ray Spectrometry

The standard “ASTM F2617-15 Standard test method for identification and quantification of chromium, bromine, cadmium, mercury, and lead in polymeric materials using energy-dispersive X-ray spectrometry” developed by the American Society for Testing and Materials (ASTM) describes the energy-dispersive X-ray fluorescence spectrometric procedure for identification and quantification of chromium, bromine, cadmium, mercury, and lead in polymeric materials.

This test method is not valid for determining total concentrations of polybrominated biphenyls (PBB), polybrominated diphenyl ethers (PBDE), or hexavalent chromium. This test method cannot be used to determine the valence states of atoms or ions.

This test method is applicable for chromium, bromine, cadmium, mercury and lead in polymeric materials in the range of 20 mg/kg to approximately 1 weight percent. This test method is also applicable for homogeneous polymeric material.

For the purposes of this standard, definitions of terms applied to XRF (X-ray fluorescence), plastics, and declarable substances are found in ASTM E135-21, ASTM D883-22, and ASTM F2576-09, respectively. In addition, the following terms and definitions apply:

• Compton scattering refers to the inelastic scattering of an X-ray photon by its interaction with bound electrons of an atom. This process is also called incoherent scattering.
• Rayleigh scattering refers to the elastic scattering of an X-ray photon by its interaction with bound electrons of an atom. This process is also called coherent scattering.

The measured count rate of Compton and Rayleigh scattered radiation varies with sample composition and can therefore be used to compensate for matrix effects. One option is to use the measured count rate of Compton scattering in the same way as the measured count rate of an internal standard element. Alternatively, the measured count rate of Compton scattering or the Compton/Rayleigh scattering ratio can be used indirectly to estimate the effective mass absorption coefficient of the sample used to compensate for matrix effects. The concept of corrections based on the Compton scattering effect is discussed in this standard as an optional part of the various calibration options.

• The fundamental parameters (FP) model is a model for calibrating the X-ray fluorescence response, including correction for matrix effects, based on theory describing the physical processes of X-ray interactions with matter.
• A homogeneous polymeric material is considered homogeneous for XRF when the elemental composition of the polymeric material is independent of the measured location on the sample and between individual samples prepared from the same polymeric material.
• Infinite thickness (or critical thickness) is the specimen thickness at which increasing it does not result in an increase in the intensity of secondary X-rays, due to absorption by the polymer matrix. This thickness varies with secondary X-ray energy or wavelength.

When performing the test, the optimum test sample is a smooth plate or disk large enough to cover the imaging area of ​​the spectrometer. Suitable samples may be molded from extruded sheets or molded from resin pellets, powders, or granules.

The sample is placed in the X-ray beam and the appropriate region of its spectrum is measured to obtain the count rates or fluorescence intensities of lead, mercury, cadmium, chromium and bromine.

Energy dispersive X-ray fluorescence (EDXRF) spectrometers are calibrated using one of several approaches, including empirical, classical curve construction from measured polymer reference materials, with fundamental parameters and empirical or theoretical influence coefficients. Calibration can be performed by the manufacturer or the user.

The selection of appropriate characteristic X-ray lines and spectrometer test conditions can vary with each element and with factors such as detector response, concentration range, and other elements present in the polymer matrix.

This test method is designed for the determination of chromium, bromine, cadmium, mercury and lead in homogeneous polymeric materials. The test method can be used to determine the conformity of the tested product to manufacturing specifications. A typical measurement time is 5 to 10 minutes per sample, depending on the sample matrix and the capabilities of the EDXRF spectrometer.

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