F-7 Minimal Use of Standards for Quantifying Trace Elements in Plastics

Abstract

The minimum requirements for standards when quantifying trace elements in plastics by X-ray fluorescence (XRF) have been investigated. The fundamental parameters method, backed up by one or more standards, is used to translate XRF intensities into quantitative information about trace element concentrations. The method includes accounting for variations in sample thickness using scattered radiation. Of course, the method works best if the standards contain certified values of all of the trace elements of interest in a matrix identical to the unknown. However, we have had reasonable success using only a single element from a plastic standard as a calibrant. The presence of uncertified and uncalibrated elements in both the standards and the unknowns can also have a significant affect on the results, depending on how such elements are treated in the fundamental parameters method. We have also investigated using standards based on a different matrix than the unknown, such as polyvinyl chloride standards for analyzing various other plastic resins and water-based standards for analysis of trace elements in oil. Standard deviations are typically 10% to 15% relative when all elements are calibrated from a standard, and up to 20% when minimum use is made of standards.

Quantitative X-ray fluorescence analysis of samples of less than ‘infinite thickness’: Difficulties and possibilities

“…The samples were pressed into pellets [51,54], collected onto membrane filter or Mylar [53], or analyzed as powders [50]. Elam and coworkers [55,56] determined RoHS elements (Restriction of Hazardous Substances Directive adopted by the European Union) in plastics by means of FP method using scattered radiation for compensation of thickness variations. Elements such as Cl, Cr, Hg, Pb, Br, Cd and Se were quantified in polyethylene, polyvinyl chloride, polyester of various loadings and thicknesses (from 4 to 14 mm).…”