High throughput identification of carbonyl compounds in natural organic matter by directional derivatization combined with ultra-high resolution mass spectrometry

Carbonyl compounds are an important component of natural organic matter (NOM), widely distributed in atmosphere, water, soil and organisms. However, our understanding on the molecular composition of these carbonyl compounds is still limited due to the lack of efficient analytical method. Here, we developed a non-targeted screening method to high-throughput detect carbonyl molecules in complex NOM samples by combining chemical derivatization with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The carbonyl molecules occupied high relative abundance (45%-70%) in six different types of dissolved organic matter (DOM) samples. Carbonyl molecules displayed lower unsaturation level, lower molecular weight, and higher oxidation degree compared to non-carbonyl molecules. More importantly, the measured abundances of carbonyl molecules showed a strong linear relationship with the results of 13C nuclear magnetic resonance analysis, suggesting the high reliability of the new method. Based on this method, we found that carbonyl molecules can be produced at DOM-ferrihydrite interface, thus playing a role in shaping the molecular diversity of DOM. This method has broad application prospects in screening carbonyl compounds from complex mixtures, and the same strategy can be used to directional identification of other functional molecules as well.