Compound-specific radiocarbon dating often requires working with small sample sizes (< 100 µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, which is introduced to the samples during processing (i.e., isolating single compounds from a heterogeneous mixture) prior to AMS measurements (procedure blank). Contamination sources include solvents, column bleed (from preparative HPLC and GC), carry-over and atmospheric carbon during combustion and vacuum line handling. Reporting accurate radiocarbon dates thus requires a correction for the procedure blank. We present our approach to assess the F14C and the mass of the blanks introduced during the preparation procedures of lipid biomarkers and lignin phenols. The treatments of these compound classes differ significantly which may lead to different F14Cblank and mblank. In order to assess the procedure blanks, we isolated fatty acids and lignin phenols from differently sized aliquots (20-80 µgC) obtained from standard materials with known F14C. Each compound class was extracted from two standard materials (one fossil, one modern). The measured F14C of the processed aliquots were graphically correlated to 1/mass of the respective sample. For aliquots of both, fossil and modern standard materials, this yielded an inverse linear relationship between the F14C and the sample size. The intercept of the regression lines obtained from the aliquots of fossil and modern standards is used to infer F14Cblank and mblank. The uncertainties of F14Cblank (σF14Cblank) and mblank (σmblank) were determined by the regression coefficients R2 of the linear regressions. Assuming constant contamination during processing of individual samples, the F14Cblank and mblank can be used to correct AMS results of lignin and lipid samples by isotopic mass balance.