Isotope-coded derivatization (ICD) was evolved as an intelligent approach, alternative to isotope internal standards, that could overcome matrix effects and instrumental drifts that usually happen during the LC-MS/MS analysis. In ICD, heavy and light forms of the derivatization reagents are reacted with the analytes introducing two different mass tags, and the heavily tagged analyte is used as a self-internal standard. Herein, we report the first ICD approach for simultaneous labeling of the α-dicarbonyl compounds; α-keto aldehydes and α-keto acids, based on their reaction with benzaldehyde and 14N/15N-ammonium acetate followed by LC/ESI+-MS/MS. Upon the ICD reaction, either imidazole or oxazole derivatives are produced when the analytes are α-keto aldehydes or α-keto acids, respectively (Figure 1). The ICD reaction proceeded to completion in 5 minutes at 80 °C. The developed method was then applied for the determination of the level of α- dicarbonyl compounds in canola oil samples and monitored the fluctuation in their level upon heating. Canola oil contains a high amount of unsaturated fatty acids that are easily decomposed by heating at high temperatures, and many carbonyl and α- dicarbonyl compounds are produced imparting the oil unpleasant odors and possible harmfulness. Our method could determine the α-dicarbonyl compounds in canola oil samples with sensitivity down to 0.1-7.0 nM for α-keto aldehydes and 1.0-43.0 nM for α-keto acids. After analysis of fresh and heated oil samples, it was demonstrated that heating of oil, elevated the level of some α-dicarbonyl compounds where glyoxal and pyruvic acid were the most elevated. In conclusion, an intelligent ICD approach for α-dicarbonyl compounds was developed using commercially available reagents avoiding the need for expensive and tedious multistep synthetic procedures and the reliability of the method was demonstrated through the successful determination of α-dicarbonyl compounds in canola oil samples.

Development of a smart isotope-coded derivatization approach for simultaneous analysis of α-keto aldehydes and α-keto acids using benzaldehyde and 14N/15N-ammonium acetate co-reagents

ACS Fall 2021

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