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Fossil Fuel Standard Reference Materials


To support regulatory and industry requirements for reference materials and standards, NIST produces and maintains a large inventory of fossil fuel SRMs that are certified for sulfur and other trace elements, including mercury and chlorine. This inventory supports the complete spectrum of the fossil fuel energy industry, and includes coals, cokes, crude oils, gasolines, fuel oils, diesel fuels, and waste materials from coal combustion, such as fly-ash. The program is continually adapting to meet the rapidly changing needs of the energy sector.


Photograph of a labeled amber bottle containing SRM 2683c Bituminous Coal.

SRM 2683c Bituminous Coal (Nominal Mass Fraction 2 % Sulfur)

Credit: NIST

The regulatory requirements with respect to air quality and fossil fuel specifications are continually changing, and consequently the associated measurement needs of the fossil fuel energy industries also change. For example, in recent years there has been a dramatic reduction in the allowable sulfur concentration of on-road diesel fuels, and the introduction of cleaner ultra-low sulfur diesel fuels (ULSD) worldwide. In the US, the allowable concentration is now 15 μg/g (ppm), and the European Union is also moving towards a Euro V standard with a reduction to 10 μg/g targeted in 2009. The economic impact of NIST diesel fuel and coal SRMs for sulfur has been well documented in an economic impact study conducted by the Research Triangle Institute in 2000. This impact study is not a static document or metric, and large benefits to these industries from the fossil fuel SRM program continue to accrue. Although sulfur will always be the principal focus in both liquid and solid fuels, mercury and chlorine are increasingly becoming a concern to the coal production and electric utility industries, and therefore there is a need for reference materials and standards to support accurate measurements of these pollutants. Similarly, with the recent concern over the impact of greenhouse gases on climate change, there will be more focus in the future on the carbon budget and its role in the energy production cycle. It is increasingly likely that carbon emission reductions will soon be subject to more stringent environmental regulations, possibly as part of a cap-and-trade program in the US. There will therefore be an increasing need for primary traceability of carbon measurements associated with such a program. 

The implementation of improved pollutant capture devices in the electric utility industry employing coal combustion has resulted in new technical challenges, as large amounts of waste products, such as fly-ash, are being generated that contain steadily rising levels of pollutants such as sulfur and mercury. To assess the environmental impact of the disposal or re-use of these waste products, commutable matrix SRMs are critically needed for the fossil fuel waste management sector. 

Major Accomplishments

  • Highly accurate measurement methods for the determination of both mercury and chlorine in solid and liquid fossil fuels have been developed and are being utilized routinely in renewals of fossil fuel SRMs.       
  • Sulfur has been determined in candidate liquid fossil fuel SRMs using a sulfur-specific bench-top XRF unit in conjunction with the standard addition method (SAM).        
  • An instructional video and computer program have been developed to implement the SRM mixing protocols for the gravimetric preparation of intermediate NIST traceable standards.

Additional Technical Details

A measurement program is maintained to support both the renewal of existing fossil fuel SRMs and the development of new SRMs that meet the emerging measurement needs of the fossil fuel energy industries. High-accuracy measurement methods using isotope dilution mass spectrometry (IDMS), X-ray fluorescence spectrometry (XRF), and the nuclear methods comprising prompt gamma activation analysis (PGAA) and instrumental neutron activation analysis (INAA), continue to be used for the measurement of sulfur and other trace elements in fossil fuel materials. An area of focus is the more efficient use of measurement resources, which has resulted in a research program to measure sulfur by more rapid methods than thermal ionization mass spectrometry (TIMS) without compromising data quality. Research is starting on the determination of sulfur by isotope dilution using a recently installed multi-collector inductively coupled plasma-mass spectrometer (ICP-MS). The same approach is also being used to develop a new high-accuracy method for the determination of carbon in coal with the aim of providing certified values for carbon in both existing and future SRMs. Work is continuing on the development of a binary blending procedure that will permit SRM users to produce their own customized reference materials from two parent end-member SRMs. To implement this system and provide practical tools for the user, an instructional video has been prepared, and software tools for automating end-member selection, gravimetric calculations, and uncertainty propagation have also been developed.


Created December 31, 2008, Updated October 24, 2023