Abstract Nitrogen pollution of air can occur from combustion of fossil fuels contaminated with fossilized nitrogen bearing organic molecules. Upgrading and refining processes have been designed to remove nitrogen but analytical monitoring feedstocks and products in real time is impractical with standard analytical techniques for nitrogen. In this study, magnetic circular dichroism (MCD) detection and quantitation of fossil porphyrins is shown to correlate well with total nitrogen in fractions representing over 80% of crude oil. Non-linear correlation in the heaviest fraction due to non-porphyrin neutral substances can be recognized and corrected. The resulting MCD procedure has the potential to become a fast on-site quality control system for upgrading crude oil.