One use of a calibration curve in analytical chemistry is to calculate the potential toxicity of a substance by comparing it to values of a prepared solution of a similar or related substance with known toxicological characteristics. In GC-HARMS, the responses of petrogenic PAH of unknown toxicity in the CALUX bioassay were compared to bioassay responses of benzo[a]pyrene (B[a]P), a much studied PAH with known toxicological properties. In this case B[a]P served as a calibration standard – or benchmark – for determining potential toxicity of the other, less formally characterized PAH detected in samples through GC-MS analysis.