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CID mass spectrum of ion at m/z 845 with exact mass measurement (mass resolution of ∼10,000 FWHM) (A). Structure of one of the possible N-alkylprotoporphyrin IX isomers (depending on which pyrrole nitrogen is alkylated) (B). Experimental (C) and theoretical (D) isotopic distribution pattern for chlorinated N-alkylprotoporphyrin.
