Comparing the selectivity and chiral separation of d- and l- fluorenylmethyloxycarbonyl chloride protected amino acids in analytical high performance liquid chromatography and supercritical fluid chromatography; evaluating throughput, economic and environmental impact

Free and Esterified Tocopherols, Tocotrienols and Other Extractable and Non-Extractable Tocochromanol-Related Molecules: Compendium of Knowledge, Future Perspectives and Recommendations for Chromatographic Techniques, Tools, and Approaches Used for Tocochromanol Determination

Free and esterified (bound) tocopherols, tocotrienols and other tocochromanol-related compounds, often referred to "tocols", are lipophilic antioxidants of great importance for health. For instance, α-tocopherol is the only tocochromanol with vitamin E activity, while tocotrienols have a positive impact on health and are proposed in the prevention and therapy of so-called modern diseases. Tocopherols, tocotrienols and plastochromanol-8 are the most well-known tocochromanols; in turn, knowledge about tocodienols, tocomonoenols, and other rare tocochromanol-related compounds is limited due to several challenges in analytical chemistry and/or low concentration in plant material. The presence of free, esterified, and non-extractable tocochromanols in plant material as well as their biological function, which may be of great scientific, agricultural and medicinal importance, is also poorly studied. Due to the lack of modern protocols as well as equipment and tools, for instance, techniques suitable for the efficient and simultaneous chromatographical separation of major and minor tocochromanols, the topic requires attention and new solutions, and/or standardization, and proper terminology. This review discusses the advantages and disadvantages of different chromatographic techniques, tools and approaches used for the separation and detection of different tocochromanols in plant material and foodstuffs. Sources of tocochromanols and procedures for obtaining different tocochromanol analytical standards are also described. Finally, future challenges are discussed and perspective green techniques for tocochromanol determination are proposed along with best practice recommendations. The present manuscript aims to present key aspects and protocols related to tocochromanol determination, correct identification, and the interpretation of obtained results.

Polysaccharides as separation media for the separation of proteins, peptides and stereoisomers of amino acids

Reliable separation of peptides, amino acids and proteins as accurate as possible with the maximum conformation and biological activity is crucial and essential for drug discovery. Polysaccharide, as one of the most abundant natural biopolymers with optical activity on earth, is easy to be functionalized due to lots of hydroxyl groups on glucose units. Over the last few decades, polysaccharide derivatives are gradually employed as effective separation media. The highly-ordered helical structure contributes to complex, diverse molecular recognition ability, allowing polysaccharide derivatives to selectively interact with different analytes. This article reviews the development, application and prospects of polysaccharides as separation media in the separation of proteins, peptides and amino acids in recent years. The chiral molecules mechanism, advantages, limitations, development status and challenges faced by polysaccharides as separation media in molecular recognition are summarized. Meanwhile, the direction of its continued development and future prospects are also discussed.

Performance comparison of chlorinated chiral stationary phases in supercritical fluid chromatography for separation of selected pyrrolidone derivatives

The effects of two chlorinated chiral stationary phases, namely, Lux Cellulose-2 and Lux i-Cellulose-5, flow-rate, percentage of co-solvent and chemical structures of the compounds on retention and resolution were studied within this article. In this work a backpressure of 150 bar, a temperature of 40 °C and 10% of methanol as co-solvent were chosen as operating conditions. The optimum flow-rate was 2 mL/min. The percentage of co-solvent was studied between 7.5% and 15%. We have observed that 15% of methanol gave the best results for most of the compounds. For all the derivatives, the Lux Cellulose-2 provided better resolutions going from 1.50 to 3.59 compared with Lux i-Cellulose-5.

Chiral Discrimination of DL-Amino Acids by Trapped Ion Mobility Spectrometry after Derivatization with (+)-1-(9-Fluorenyl)ethyl Chloroformate

A novel analytical method based on hybrid trapped ion mobility spectrometry-time-of-flight mass spectrometry (TIMS-TOFMS) has been developed to achieve fast enantiomeric separation of amino acids (AAs). Resolution of chiral AAs was achieved by forming diastereomers through derivatization with the chiral agent (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC), avoiding the use of reference compounds. Electrospray ionization (ESI) in positive mode yielded sodiated FLEC-AAs ions of which the diastereomers could be separated by TIMS. The effect of other alkali metal ions (such as Li and K) on the enantioselectivity was studied, but chiral discrimination was only observed for Na. TIMS conditions, including voltage ramp, ramp time, and accumulation time were optimized for each AA, and collision cross sections (CCSs) were determined for all diastereomers. The migration order of the DL enantiomers was found to be dependent on the structure of the AA. The resulting TIMS resolution (K0/ΔK0) for the FLEC-AA diastereomers on average was 115, requiring a mobility (K0) difference of about 0.009 cm²/(V s) to achieve 50%-valley separation. From the 21 AAs studied, enantiomer separation was achieved for 17 AAs with mobility differences ranging from 0.009 for lysine up to 0.061 cm²/(V s) for asparagine. Moreover, the presented methodology provided mutual separation of various AAs, allowing chiral analysis of multiple AAs simultaneously which may be challenging with previous enantioselective IMS approaches. It appeared possible to fully resolve all studied DL-AAs using three distinct TIMS methods, resulting in a total MS run time of about 3 min (1 min per method) and a total analysis time (including derivatization) of less than 15 min. The method demonstrated capable to determine enantiomeric ratios down to 2.5% with detection limits for the D enantiomers in the nanomolar range. This new TIMS-based methodology opens up possibilities for easy and fast analysis of AA enantiomers.

Rapid Separation of All Four Tocopherol Homologues in Selected Fruit Seeds via Supercritical Fluid Chromatography Using a Solid-Core C18 Column

Tocopherol separations employing the same Kinetex™ C18 column via supercritical fluid chromatography (SFC) and reversed-phase liquid chromatography (RP-LC) were compared. The application of the SFC system with UV diode array detection (DAD) resulted in rapid separation of all four tocopherol homologues with a total analysis time below 2 min. The RP-LC approach could not separate the isomers β and γ. The developed SFC-DAD method was precise, accurate, and most importantly more environmentally friendlier compared to the RP-LC method due to the 125-fold decrease in methanol consumption. The present study illustrated the selectivity differences between LC and SFC and how the C18 column can be used for tocopherol characterization. The optimized SFC method was successfully applied for the tocopherol determination in the seeds of nine different fruit species.