Energy-Resolved Ion Mobility Spectrometry: Composite Breakdown Curves for Distinguishing Isomeric Product Ions

Abstract

Identification of lipopeptides (LpAA) synthesized from bacteria involves the study of structural characterization. Twenty LpAA have been characterized using commercial tandem high-resolution mass spectrometers in negative electrospray, employing nonresonant excitation in "RF only" collision cells and generally behave identically. However, [LpAA-H] − (AA = Asp or Glu) shows surprising fragmentation pathways, yielding a complementary fatty acid carboxylate and dehydrated amino acid fragment anions. In this study, the dissociation mechanisms of [C12Glu-H] − were determinate using energy-resolved mass spectrometry (ERMS). Product ion breakdown profiles are, generally, unimodal with full width at half-maximum (fwhm) increasing as product ion m/z ratios decrease, except for the two product ions of interest (fatty acid carboxylate and dehydrated glutamate) characterized by broad and composite profiles. Such behavior was already shown for other ions using a custom-built guided ion beam mass spectrometer. In this study, we investigate the meaning of these particular profiles from an ERMS breakdown, using fragmentation mechanisms depending on the collision energy. ERMS on line with ion mobility spectrometry (IMS), here called ER-IMS, provides a way to probe such questions. Broad or composite profiles imply that the corresponding product ions may be generated by two (or more) pathways, resulting in common or isomeric product ion structures. ER-IMS analysis indicates that the fatty acid carboxylate product ion is produced with a common structure through different pathways, while dehydrated glutamate has two isomeric forms depending on the mechanism involved. Drift time values correlate with the calculated collision cross section that confirms the product ion structures and fragmentation mechanisms.

Charge‐solvated versus protonated salt forms of cyclodepsipeptide toxins in electrospray: Dissociation of alkali‐cationized forms enables straightforward sequencing of cereulide

“…Recorded with a particular instrument tuning and calibration allowing alkali detection using Qq/TOF instrument, ERMS breakdown curves of the [M + NH 4 ] + ( m/z 1170), [M + Li] + ( m/z 1159), [M + Na] + ( m/z 1175), and [M + K] + ( m/z 1191) were compared. Especially, (i) their relative abundances (Figure 3) and (ii) their absolute abundances 46 (Figure 4) were explored. The main characteristics of the PIC, TPIC, or TPIC* and alkali cation profiles from ERMS with relative abundance (Figure 3) are reported in Table S3.…”

“…1175), and [M + K] + (m/z 1191) were compared. Especially, (i) their relative abundances (Figure 3) and (ii) their absolute abundances 46 (Figure 4) were explored. The main characteristics of the PIC, TPIC, or TPIC* and alkali cation profiles from ERMS with relative abundance (Figure 3) are reported in Table S3.…”

“…Instead of the default calibration (Figure S2) where alkali cation detection is systematically missed, the choice to use low m/z calibration (Figures 3 and 4 4), as described in a recent study. 46 To simplify the study of these breakdown profiles, each of the alkali cation profiles was compared to a profile resulting from the absolute abundance sum of the other numerous product ions (i.e., TPIC*; Figure 4B-D). In addition to the…”

“…The scattering effect at the highest E Lab is all the more pronounced as the m/z is low 44,45 (Lesage et al, to be published). To our knowledge, such an approach to evaluate the effect of scattering on the detection of Li + , Na + , and K + has never been performed using commercial instruments 46,47 . This study documents (i) the driving force leading to the CBC responsible for the formation of the most representative product ions of the cereulide sequences, (ii) the double origin of K + release, and (iii) the choice of the alkali‐cationized cereulide to sequence the cereulide with the highest sensitivity.…”

Energy Resolved Mass Spectrometry for Interoperable Non-resonant Collisional Spectra in Metabolomics

“…Recently, using two different Qq/TOF instruments operated by different users, we demonstrated a high interinstrument reproducibility of energy-resolved mass spectrometry (ERMS) breakdown curves for deprotonated lipo-amino acids (aspartic and glutamic acids linked to lauric acid, Figure S1). 5,6 The ERMS of protonated leucine-enkephalin, recorded on a Qq/ TOF and a Qq/LIT/Orbitrap, have been studied to find a correlation between E Lab values that result in a satisfactory similarity of PIS. 7 In the present study, we show that singular points (called here descriptors) deduced from ERMS breakdown curves can be exploited to determine instrument-specific E Lab values at which comparable PIS can be recorded and become comparable across platforms.…”