Enantioselective multiple heart cutting online two-dimensional liquid chromatography-mass spectrometry of all proteinogenic amino acids with second dimension chiral separations in one-minute time scales on a chiral tandem column

In this work, we present a unique, robust and fully automated analytical platform technology for the enantioselective amino acid analysis using a multiple heart cutting RPLC-enantio/stereoselective HPLCESI-QTOF-MS method. This D-2-LC method allows the full enantioselective separation of 20 proteinogenic AAs plus 5 isobaric analogues, namely allo-Threonine (aThr), homoserine (Hse), allo-isoleucine (aIle), tert-Leucine (Tle) and Norleucine (Nle), after pre-column derivatization with 6-aminoquinolyl-N- hydroxysuccinimidyl carbamate (AQC; AccQ). This N-terminal AA-derivatization method introduces on the one hand beneficial chromatographic properties for D-1 RP-LC (stronger retention) and D-2 chiral separation (better chiral recognition), and on the other hand favorable detection properties with its chromophoric, fluorophoric, and easily ionizable quinoline mass tag. The entire separation occurs within a total 2DLC run time of 45 min, which includes the D-1-RP run and the 68 s D-2 chiral separations of 30 heart-cuts (from the D-1-RP-run) on a chiral quinine carbamate (core-shell QNAX/fully porous ZWIX) tandem column. This relatively short overall run time was only possible by utilizing the highly efficient smart peak parking algorithm for the heart cuts and the resulting optimized analysis order thereof. D-1 retention time precisions of <0.21% RSD were a requirement for the time-based sampling mode and finally led to a robust, fully automated enantioselective amino acid analysis platform. This achiral-chiral 2DLC method was applied for the amino acid stereoconfiguration assignment of three peptides (aureobasidin A, a lipopeptide research sample, and octreotide) using an L-[u-(CN)-C-13-N-15] labelled internal AA standard mix spiked to each sample. The isotopically labelled L-AA standard allowed an easy and straightforward identification and configuration assignment, as well as the relative quantification of amino acids within the investigated peptides, allowing the direct determination of the number of respective amino acids and their chirality within a peptide. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study introduces a unique and fully automated analytical platform technology for enantioselective amino acid analysis, demonstrating high stability and accuracy in separation and detection.