A method of determining adulteration of a fuel comprising: (i) acquiring a fuel sample, wherein the fuel sample comprises (a) a fuel, and (b) a compound characterized by Formula I: wherein X can be carbon, oxygen, or sulfur; wherein, when X is C, R 1 and R 2 can each independently be hydrogen, a C 1 to C 20 alkyl group, or a C 6 to C 10 aryl group; wherein, when X is O or S, R 1 and R 2 are lone non-bonding electron pairs; R 3 and R 3' can each independently be hydrogen or a C 1 to C 4 alkyl group; R 4 and R 4' can each independently be hydrogen, a C 1 to C 4 alkyl group, a C 4 to C 10 cycloalkyl group, or a C 6 to C 10 aryl group; R 5 and R 5' can each independently be a C 4 to C 10 alkyl group; R 6 and R 6' can each independently be hydrogen or a C 1 to C 6 alkyl group; and R 7 and R 7' can each independently be hydrogen or a C 1 to C 4 alkyl group; (ii) adding a known amount of a heavy compound to the fuel sample to yield a marked fuel mixture, wherein the heavy compound comprises a compound of Formula I having at least one atom replaced with deuterium ( 2 H); (iii) subjecting the marked fuel mixture to an analytical technique to record an analytical signal for the compound characterized by Formula I and an analytical signal for the heavy compound; (iv) comparing the analytical signal for the known amount of heavy compound to the analytical signal for the compound characterized by Formula I; (v) determining a ratio of an amount of the compound characterized by Formula I to the known amount of the heavy compound in the marked fuel mixture; and (vi) calculating the amount of the compound characterized by Formula I in the marked fuel mixture. (i) acquiring a fuel sample, wherein the fuel sample comprises (a) a fuel, and (b) a compound characterized by Formula I: wherein X can be carbon, oxygen, or sulfur; wherein, when X is C, R 1 and R 2 can each independently be hydrogen, a C 1 to C 20 alkyl group, or a C 6 to C 10 aryl group; wherein, when X is O or S, R 1 and R 2 are lone non-bonding electron pairs; R 3 and R 3' can each independently be hydrogen or a C 1 to C 4 alkyl group; R 4 and R 4' can each independently be hydrogen, a C 1 to C 4 alkyl group, a C 4 to C 10 cycloalkyl group, or a C 6 to C 10 aryl group; R 5 and R 5' can each independently be a C 4 to C 10 alkyl group; R 6 and R 6' can each independently be hydrogen or a C 1 to C 6 alkyl group; and R 7 and R 7' can each independently be hydrogen or a C 1 to C 4 alkyl group; (ii) adding a known amount of a heavy compound to the fuel sample to yield a marked fuel mixture, wherein the heavy compound comprises a compound of Formula I having at least one atom replaced with deuterium ( 2 H); (iii) subjecting the marked fuel mixture to an analytical technique to record an analytical signal for the compound characterized by Formula I and an analytical signal for the heavy compound; (iv) comparing the analytical signal for the known amount of heavy compound to the analytical signal for the compound characterized by Formula I; (v) determining a ratio of an amount of the compound characterized by Formula I to the known amount of the heavy compound in the marked fuel mixture; and (vi) calculating the amount of the compound characterized by Formula I in the marked fuel mixture.