Online chiral selector screening by parallel post-column infusion-LC-MS/MS to enable enantiomeric measurements

Chiral selector (CS) serves as the determinant role for chiral MS/MS; however, the success of CS pursuit relies heavily on the experiences and fortunes. Inspired by either the CS or the enantiomer within the metal ion (e.g., Cu²⁺)-scaffolded diastereomeric complexes plays both host and guest roles, a smart strategy was proposed for online CS screening through fortifying enantiomeric CSs (e.g., D/L-Pro) in parallel to LC-energy-resolved MS/MS via post-column infusion (PCI). Attributing to structural diversity features, several herbal medicines (HMs) were screened to capture CSs. The strategy utility was justified by measuring a mixture containing several known CSs and some negative controls, and as desired, all CSs and nonetheless, none negative control, were captured. Through applying the two prerequisites that diastereomeric complex ions formation and their different MS/MS behaviors, twelve compounds appeared as eligible CSs from Peucedani Radix. Representatively, (3'R,4'R)-3'-acetyl-4'-isobutyryl-cis-khellactone (AIK) was purified and structurally identified. Moreover, the different MS/MS behaviors of the complex ions such as [Cu^II(D/L-AA)(AIK)₂-H]⁺ were explored in depth by constructing full collision energy ramp (FCER)-MS² spectrum and conceptually clarified via quantum structural calculation. Through applying the kinetic method, AIK facilitating chiral MS/MS was validated by simultaneous enantiomeric excess (e.e.) determination of ten pairs of amino acid enantiomers in mimic samples and cell culture medium. The current study offers some CSs for chiral MS/MS and more importantly, provides a meaningful tool namely parallel PCI-LC-MS/MS for online CSs screening from the complicated matrices, e.g., HMs.