<jats:title>ABSTRACT</jats:title><jats:p>Compound-specific radiocarbon (<jats:sup>14</jats:sup>C) dating often requires working with small samples of &lt; 100 µg carbon (µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F<jats:sup>14</jats:sup>C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. <jats:italic>n</jats:italic>-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6–151 µgC) of <jats:italic>n</jats:italic>-alkanoic acids and lignin phenols obtained from standard materials with known F<jats:sup>14</jats:sup>C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F<jats:sup>14</jats:sup>C. There is an inverse linear relationship between the measured F<jats:sup>14</jats:sup>C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We use Bayesian methods to fit linear regression lines between F<jats:sup>14</jats:sup>C and 1/mass for the fossil and modern standards. The intersection points of these lines are used to infer F<jats:sup>14</jats:sup>C<jats:sub>blank</jats:sub> and <jats:italic>m</jats:italic><jats:sub>blank</jats:sub> and their associated uncertainties. We estimate 4.88 ± 0.69 μgC of procedural blank with F<jats:sup>14</jats:sup>C of 0.714 ± 0.077 for <jats:italic>n</jats:italic>-alkanoic acids, and 0.90 ± 0.23 μgC of procedural blank with F<jats:sup>14</jats:sup>C of 0.813 ± 0.155 for lignin phenols. These F<jats:sup>14</jats:sup>C<jats:sub>blank</jats:sub> and <jats:italic>m</jats:italic><jats:sub>blank</jats:sub> can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.</jats:p>