Background on XRF Testing, Detailed Methodology
and Methodological Limitations
HealthyStuff.org product tests are performed with a portable X-ray
Fluorescence (XRF) analyzer. XRFs are widely used by both product
manufacturers and government regulators to screen consumer products
for hazardous chemicals. XRFs, like all test methods, have limitations.
Researchers selected products based on our research interests and
consumer interest. The sampling was not random or necessarily designed
to be representative of all products on the market. This page provides
an overview of the product testing methodology used by HealthyStuff.org,
XRF Testing Methodology
Researchers tested products using a High Definition X-Ray Fluorescence (HDXRF)
manufactured by X-Ray Optical Systems (download XRF
Factsheet). The HDXRF analyzer uses a technology known as x-ray
fluorescence spectrometry to detect chemical elements, such as lead,
cadmium, chlorine, arsenic, mercury, tin, and antimony. The major benefit
of HDXRF is that monochromatic excitation eliminates the X-ray scattering
background under the fluorescence peaks, greatly enhancing detection
performance. This analytical approach results in detection limits in
the parts-per- billion (ppb) range for many elements of interest in
a variety of materials.
Typical HDXRF element detection levels
The elemental composition of the materials reveals the presence of potentially
hazardous chemicals, such as metals, and also allows researchers to infer the
possible presence of toxic chemicals or materials, including brominated flame
retardants (BFRs), polyvinyl chloride (PVC) and possibly phthalate plasticizers.
We have translated the research results into a HealthyStuff.org product rating
system to allow users to easily compare the chemical levels of a variety of
consumer products. There are a number of chemicals of concern that cannot be
detected by this technology.
X-ray Flourescence (XRF) Background Material
- Comparison of Testing of Plastics
for Lead by X-ray Fluorescence and Traditional Nitric Acid Digestion/ GFAA
After Muffle Furnace Combustion, November 8, 2008. Danielle Cappellini,
B.Sc., MHA and Woodhall Stopford, MD, MSPH, Duke University School of Medicine.
From the Study: "Originally billed as a "screening" technique,
these results suggest that in the range of concern, x-ray fluorescence can be
used to determine accurately the presence of excessive levels of lead in plastic
- Study of the Effectiveness, Precision, and Reliability of X-ray Fluorescence Spectrometry and Other Alternative Methods for Measuring Lead in Paint, August, 2009. U.S. Consumer Product Safety Commission
From the Study: "With appropriate test methods and SRMs[Standards
Reference Materials], XRF spectrometry is suitable in many cases for the the
determination of lead in polymers. CPSC staff has conducted comparison tesing
of plastic samples and SRMs by XRF and by using current wet chemical methods
and found generally good agreement. XRF produced good results on homogeneous
plastic SRMs with certified concentrations as low as 13.6 parts per million (ppm)."
- Linking PBDEs in House Dust to Consumer Products using X-ray Fluorescence, Allen, Joeseph, et. al., Environmental Science and Technology April 30, 2008.
From the Study: "The portable XRF analyzer appears to be a promising tool for characterizing the bromine content of products in homes and improves our understanding of the extent to which such products may act as sources of PBDEs in the indoor environment."
- Common Research Uses for XRF Technology
- Summary or Detailed Review
with Abstracts A summary of over 80 peer review research papers, from
dozens of research areas, which utlized XRF testing as a core analytical
method. XRF analyzers are usd by US Customs, FDA, EPA, DOE, & Consumer Agencies.
Read more about the use of XRFs for compliance screening.
Quality Assurance/Product Variation - In order to evaluate
the variation per product to assess and verify the accuracy of our testing,
some repeat samples were taken. This process took place once every 200
samples, and was done for at least one product in every product category.
Repeat samples are taken in three different ways:
- three readings taken from the same sampling location of one product
- three readings taken from three different sampling locations (consisting
of the same material, color, etc.) on the same product
- three readings taken from the same sampling location on three different
but identical products
All repeat sample data was recorded and submitted for review, but is
NOT included in the product database.
Data Interpretation - We interpreted the results using
the concentrations and deviations reported by the analyzer, together with
visual examination of the spectra generated by the instrument. The analyzer
reports concentrations of elements by analyzing the spectra using reference
data for the elements it reports, and measuring the area under the curve
in the spectrum. We visually examined the spectra to confirm the presence
of elements with known interferences (lead, bromine, and arsenic), and have not reported
them where we could not confirm presence.
The levels of lead, cadmium, chlorine, and other elements shown in this
website are those reported by the HDXRF analyzer manufactured by X-Ray Operating Systems. Our testing methodology uses standards with known levels
of certain elements to check the accuracy of the analyzer in one type
of matrix material. However, the products we tested are
made of many different types of materials, in some cases even within
the same product. The prescence of materials may interfere with the analyzer's
ability to quantify the elements accurately. When the materials
in a single product are not homogeneous, the test results may vary depending
on the orientation between the object under test and the testing device.
Where the testing is not able to isolate a single material, the reported
levels may represent an averaging of the levels in the different materials.
Interferences can occur between elements as well, such as with lead and
arsenic, resulting in poorer precision. Test results are reviewed for
Therefore, the levels we report provide a general indication of the
levels in the products in order to guide consumers on product choices.
More exhaustive testing with XRF, as well as laboratory testing, could
provide more detailed findings on the levels of elements and associated
HealthyStuff.org ratings do not provide a measure of health risk or chemical exposure associated with any individual product, or any individual element or related chemical. HealthyStuff.org ratings provide only a relative measure of high, medium, and low levels of concern for several hazardous chemicals or chemical elements in an individual product in comparison to criteria established in the site methodology.