Determination of Hexavalent Chromium Fractions in Plastics Using Laboratory-Based, High-Resolution X-ray Emission...

Area of Science:

• Environmental Science
• Analytical Chemistry
• Materials Science

Background:

• Hexavalent chromium (Cr(VI)) is a known human carcinogen, posing public health risks through environmental contamination, particularly in groundwater.
• Regulatory bodies like the European Union restrict Cr(VI) due to its hazardous nature.
• Existing analytical methods for Cr(VI) characterization, especially in complex matrices like plastics, often lack sufficient accuracy due to issues like species interconversion and under-extraction during liquid extraction protocols.

Purpose of the Study:

• To address the limitations of current analytical capabilities for Cr(VI) characterization in industrial and commercial applications.
• To introduce and validate a noninvasive laboratory-based method for determining the Cr(VI)/Cr ratio in plastics.
• To provide a viable alternative to traditional liquid extraction methods for regulatory compliance testing of Cr(VI) content.

Main Methods:

• Utilized high-resolution wavelength dispersive X-ray fluorescence (WDXRF) spectroscopy, also known as X-ray emission spectroscopy (XES) in the synchrotron community.
• Employed laboratory-based XES with energy resolution near the core-hole lifetime limit for noninvasive analysis.
• Applied the method to plastic samples, including those developed by standards organizations for improved Cr(VI) testing protocols.

Main Results:

• Demonstrated the capability of laboratory XES for noninvasive, accurate determination of the Cr(VI)/Cr ratio in plastics.
• Provided proof-of-principle for XES as a reliable alternative to liquid extraction methods.
• Reported the Cr(VI) mass fraction for NIST Standard Reference Material 2859 (Restricted Elements in Polyvinyl Chloride).

Conclusions:

• Extremely high-resolution laboratory WDXRF (XES) offers a noninvasive and accurate method for Cr(VI) analysis in plastics.
• This technique can serve as a regulatory compliance alternative to current, often insufficient, liquid extraction protocols.
• The successful application to a NIST Standard Reference Material validates its practical utility for hazardous substance testing.