Enantiomer Separation of Amino Acids by Complexation with Chiral Reference Compounds and High-Field Asymmetric Waveform Ion Mobility Spectrometry:  Preliminary Results and Possible Limitations

Abstract

We present a new method for separation of enantiomers with high-field asymmetric waveform ion mobility spectrometry (FAIMS), coupled to mass spectrometric detection. Upon addition of an appropriate chiral reference compound to the analyte solution and subsequent ionization of the solution by electrospray ionization, analyte enantiomers formed diastereomeric complexes, which were potentially separable by FAIMS. The methodology being developed is intended to be general, but here amino acid analytes are specifically considered. In the examples presented herein, six pairs of amino acid enantiomers were successfully separated as metal-bound trimeric complexes of the form [MII(L-Ref)2(D/L-A)-H]+, where MII is a divalent metal ion, L-Ref is an amino acid in its L form acting as chiral reference compound, and A is the amino acid analyte. For example, D- and L-tryptophan were separated in FAIMS as [NiII(L-Asn)2(D-Trp)-H]+ and [NiII(L-Asn)2(L-Trp)-H]+. As FAIMS separation typically takes place over a time scale of only a few hundred milliseconds, the presented separation method opens new possibilities for rapid analysis of one analyte enantiomer in the presence of the other enantiomer. Preliminary quantification results are presented, which suggest that fast and sensitive quantitative chiral analyses can be performed with FAIMS. Method limitations are discussed in terms of diverse phenomena, which are not yet understood.

Ion Mobility‐Mass Spectrometry

“…(88) Also, six pairs of amino acid and terbutaline enantiomers were characterized with IMS-MS through conversion of the enantiomers to metal-bound trimeric complexes of the form [M II (L-Ref) 2 (D/L-A)-H] + . (117,170) ESI is the preferred ionization method with this chiral approach so that the interactions between the enantiomers and chiral reference are not disrupted.…”

Field Asymmetric Waveform Ion Mobility Spectrometry Analysis of Proteins and Peptides: A Review

“…The addition of divalent metal ions as a chiral reference material to D and L amino acid enantiomers resulted in the formation of diastereomeric complexes which were separable by FAIMS-MS [43]. However, a limitation of this approach was the presence of peptide enantiomer cluster ions, transmitted through the FAIMS device at different differential mobilities and fragmented in the mass spectrometer.…”

Optimum waveforms for differential ion mobility spectrometry (FAIMS)

“…The introduction of commercial DMS instruments and particularly their integration with mass spectrometry (MS) andI or liquid or gas chromatography since 2003 has enabled rapid growth of the number and diversity of applications that include environmental analyses [6,7], food and water quality assurance [8][9][10], bacterial typing [11,12], forensic investigations [13], proteomics and metabolomics [14][15][16][17], pharmaceutical studies [18][19][20], and protein folding research [21][22][23][24][25]. Since its earliest days, DMS has been employed to detect explosives, drugs, and chemical warfare agents, and its role in defense, security, and law enforcement settings continues expanding [26][27][28][29][30][31].…”