From mass to metabolite in human untargeted metabolomics: recent advances in annotation of metabolites applying liquid chromatography-mass spectrometry data

The relatively unbiased study of metabolites in biological systems is called untargeted metabolomics and the application of liquid chromatography-mass spectrometry platforms for data acquisition is now common across the world. When operating in its most unbiased form, this experimental strategy starts from assuming no knowledge of the metabolites to be detected and instead the data acquired is used to annotate or identify the detected metabolites on a
study-by-study basis. The process of metabolite annotation is a bottleneck in untargeted metabolomics and which significant progress has been made in the last ten years in understanding the limitations and developing new experimental and computational methods and tools to enhance our capabilities. In this review we will describe the current status of tools applied for metabolite annotation and discuss current areas where further work is required.