We apply Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for direct characterization of iron-porphyrins in hydrothermal liquefaction (HTL) biocrude oils derived from two algae: Tetraselmis sp. and cyanobacteria. The iron porphyrin compounds are shown to cause catalyst bed plugging during hydroprocessing due to iron deposition. Inductively-coupled plasma optical emission spectrometry (ICP-OES) was utilized for iron quantitation in the plugged catalyst beds formed through hydroprocessing of the two HTL biocrudes and identifies an enrichment of iron in the upper five centimeters of the catalyst bed for Tetraselmis sp. (Fe = 100,728 ppm) and cyanobacteria (Fe = 115,450 ppm). Direct infusion FT-ICR MS analysis of the two HTL biocrudes with optimized instrument conditions facilitates rapid screening and identification of iron porphyrins without prior chromatographic separation. With FT-ICR MS we identify 138 unique iron porphyrin compounds in the two HTL biocrudes that have similar carbon number and double bond equivalent distributions to the metal porphyrins (e.g. Ni and V) reported for petroleum. No iron porphyrins are Observed in the cyanobacteria HTL biocrude after hydroprocessing, which indicates that iron porphyrin structures in the HTL biocrude are degraded during hydrotreatment. Hydrodemetallization reactions that occur through hydroprocessing of HTL biocrudes could be responsible for the decomposition of iron porphyrin structures leading to metal deposition in the catalyst bed that result in catalyst deactivation and bed plugging, and must be addressed for effective upgrading of algal HTL biocrudes. (C) 2016 Elsevier Ltd. All rights reserved.