Since 2007 and the discovery of high amounts of lead in the paint on children’s toys (see IBO 11/15/07), handheld X-ray Fluorescence spectrometry (XRF) has attracted attention for its ability to quickly and easily screen for lead content in consumer products on site (see IBO 2/29/08). The US’s Consumer Product Safety Improvement Act of 2008 (CPSIA) specified the use of XRF as one method for testing small painted surfaces (see IBO 7/31/08). The CPSIA also required the Consumer Product Safety Commission (CPSC) to evaluate “the effectiveness, precision and reliability” of XRF for quantifying the amount of lead in surface paints and coatings on children’s products down to the 90 ppm limit specified by the CPSIA. The new limit went into effect last month.

The CPSC recently released its report on XRF. The report found that although XRF is an effective technique for screening lead in paint and other surface coatings, standard reference materials (SRMs) and standard methods need to be developed before an adequate evaluation of XRF’s use for this application can be conducted. XRF SRMs for lead in paint film are available only in a mass per area unit of measurement. However, the CPSIA requires that lead in paint be measured in a mass per mass unit of measurement. Conversion is complicated as it requires knowledge of the paint film’s thickness and density.

Asked to comment on the CPSC report, Jon Shein, director of Marketing Communications at Thermo Scientific Niton Analyzers, maker of the Niton handheld XRF system, told IBO: “We are generally pleased with the results of the report. The bottom line for the CPSC and businesses seeking to comply with the law is that XRF provides a cost effective, nondestructive means now for testing plastics, and it will likely provide the same capability for paint testing in the future.” The report confirmed the reliability of XRF for measuring lead in homogeneous plastics and the availability of SRMs and standard test methods for this application, but recommended wet chemical testing for certifying results of greater than 200 mg/kg.

Regarding the report, Satbir Nayar, product manager of HDS at XOS, a maker of benchtop XRF systems, told IBO: “We are pleased that CPSC is evaluating alternative methods for the determination of lead in paint for compliance with CPSIA and look forward to further studies on this subject based XOS HDS Technology. As indicated in the report, traditional handheld XRF is not capable of accurately detecting lead in paint layers at the current levels mandated in CPSIA.” He noted that XOS’s HD XRF is capable of quantifying lead concentrations at levels below regulated limits. “Unlike previous XRF approaches, HDS quantifies lead in paint separately from the base material, well below the current and future limits required under the CPSIA.” This is achieved through the use of multiple DCC (Doubly Curved Crystal) optics, allowing for the discrimination of lead amounts in the surface coating from lead amounts in the substrate.

Both Thermo Fisher Scientific and XOS have worked with the CPSC on XRF testing. “The CPSC used their Thermo Scientific Niton XL3t instruments for its study,” said Mr. Shein. “They also used the new Thermo Scientific Niton GOLDD (Geometrically Optimized Large Drift Detector) detection technology for paint analysis, and they found that this new unit can detect lead at the levels necessary for compliance.” The report stated that the development of handheld XRF systems with silicon drift detectors identified lead in paint films on a metal substrate that were spiked with 50 mg/kg lead naphthenate. The report also refers to XOS’s HD technology, stating it is using the technology to qualify SRM films for heterogeneity.

The CPSC and the National Institute for Standards and Technologies are currently developing SRMs for validating and calibrating in situ analysis of lead in paint films on children’s products down to 90 ppm using XRF. ASTM International is developing a handheld XRF standard for identifying and quantifying lead in paint and surface coatings on consumer products using XRF. “ASTM International approval of a Standard Test Method for determining lead in paint using HDS is well underway,” said Mr. Nayar. “The test method and research report is written and the inter-laboratory study was completed in September 2009.”

The CPSC’s report also highlights the possible use of laser induced breakdown spectroscopy (LIBS) for this application. LIBS can be adjusted to prevent substrate interference and can measure lead in paint film in mass per mass units. However, SRMs for LIBS for this application are not yet available.