High-throughput direct profiling of natural products in plant leaves using ambient ionization high-resolution mass spectrometry.

Plant leaves contain natural products that may have nutritional and medicinal values. In this work, a modified ambient ion source of angled direct analysis in real time (aDART) and high-resolution mass spectrometry (HRMS) was used for direct surface analysis of different plant leaves. Untreated leaves, leaves with the wax layer removed, and leaf imprints were all successfully analyzed by aDART-HRMS in min, observing abundant natural product information including esters, amino acids, saccharides, flavonoids, alkaloids, alcohols, and ketones/aldehydes. Different plant samples have their unique features. Fresh leaves facilitate instant analysis without sample preparation, dewaxed leaves can help expose chemicals concealed by the epidermis, and the leaf imprints can better reveal substances inside the leaf tissues. Traditional leaf extracts were compared and analyzed using DART-HRMS, and it was shown that more compounds were discovered by surface analysis. aDART-HRMS is capable of obtaining samples' composition directly from plant leaves, without destroying leaf morphology and tedious sample preparation. This modified aDART-MS technology provides a simple and robust ambient ionization method for direct characterization of natural products contained in various plant samples.