Direct chromatographic methods for enantioresolution of amino acids: recent developments

α-Amino acids are present in two opposite configurations due to the presence of a central carbon atom which is a chiral center. While l-amino acids are present in large amount in nature, only tiny quantities of their d-enantiomers exist. For a long time, d-amino acids have been considered of bacterial origin only, but recently we realized that they are present in all living organisms: notably, d-amino acids play specific and relevant functions in the different organisms. Detection and quantification of d-amino acids are mandatory to shed light on their physiological roles, especially related to foods and human health. Chromatographic techniques are among the most commonly used analytical methods for the enantioseparation of amino acids. Here, we revised the latest improvements in chromatographic direct methodologies based on chiral selectors and aimed to improve analytical speed, sensitivity, robustness, and reproducibility. While current methods are well suited for d-amino acid analysis in foodstuffs and pharmaceuticals, further improvements seem required for their simultaneous, fast and sensitive detection in biological fluids, an emerging field since d-amino acids have been proposed as biomarkers of different and relevant human pathologic states.