ASTM D6866 was written for the US Department of Agriculture to provide a measure of biomass-derived carbon to total organic carbon within carbon-containing solids, liquids, and gases. The term “biobased” is therein defined as “total biomass-derived carbon to total ORGANIC carbon.”
Biobased products like writing papers, paints, insect repellents, plastics, liquid cleaners, diesel fuel additives, and floor tiles contain inorganic carbon in significant quantities. Since ASTM D6866, by definition, only takes into account total organic carbon, inclusion of inorganic carbon in the biobased content calculation will affect the accuracy of the measurement.
It is important to know if the product submitted for ASTM D6866 testing has inorganic components so that correction factors will be applied during biobased content calculation. Biobased products with inorganic carbon that has little or no carbon 14 activity will have biobased content values that are too low if corrections will not be applied.
Inorganic carbon in biobased products is usually present in the form of carbonates. However, not all carbonate-containing biobased products have sufficient amounts of inorganic carbon to affect the accuracy of the results. Products with high organic carbon content and low inorganic carbon content will generally not be affected by the presence of the latter. Those with very low organic carbon content, on the other hand, will be affected by even small amounts of inorganic carbon because the latter constitutes a significant portion of the product’s total carbon content.
For products with inorganic carbon constituting more than 3% of the total carbon, the inorganic carbon must be excluded from the biobased content calculation. Thus, to ensure the accuracy of results, the lab must be informed if a product’s inorganic component concentration is sufficient enough to pose analytical concerns.
To be within the exact specification requirements of ASTM D6866, the carbonate component must be eliminated from the final calculation of biobased content when it does not originate from organic sources. Non-organic sources include limestone, dolomite, siderite, and any other source of carbon originating from mineral precipitation.
Applications for ASTM D6866 are realized in other industry sectors wherein carbonate can and should be included within the final calculations. These include biogenic emissions from combustors and incinerators, the cement industry, and the paper and pulp industries. As such, ASTM D6866 is directly applicable to making a precise determination for biomass-derived carbon content.
A single measurement relating “total biomass-derived carbon to TOTAL carbon” is readily available from an ASTM D6866 analysis. However, the end user must consider that including the carbonate in the result does not conform specifically to the definition of “biobased” per the ASTM D6866 standard. The inconsistency may be overcome by simply defining the result with another term (e.g. biomass CO2, renewable carbon content per carbon 14 analysis, biogenic carbon content, etc).