<p>A large
proportion of the complexity and redundancy of LC-MS metabolomics data comes
from adduct formation. To reduce such redundancy, many tools have been
developed to recognize and annotate adduct ions. These tools rely on
pre-defined adduct lists which are learned empirically from reverse phase LC-MS
studies. Meanwhile, hydrophilic
interaction chromatography (HILIC) is gaining popularity in metabolomics
studies due to better performance on polar compounds. HILIC methods typically
use high concentration of buffer salts for improved chromatography performance.
It is therefore necessary to analyze the adduct formation in HILIC
metabolomics. To this end, we developed <u>co</u>-<u>v</u>ariant <u>i</u>o<u>n</u>
<u>a</u>nalysis (COVINA) to investigate the metabolite adduct formation. Using
this tool, we completely annotated 201 adduct and fragment ions of 10
metabolites. Many of the metabolite adduct ions are found to contain cluster
ions of mobile phase additives. We further utilized COVINA to find the major
ionization forms of metabolites. Our results show that for some metabolites the
adduct ion signals can be >200-fold higher than the deprotonated form, offering
better sensitivity for targeted metabolomics analysis. Finally, we developed
the in-source CID ramping (InCIDR) method to analyze the intensity changes of
the adduct and fragment ions of the metabolites. Our analysis demonstrates a
promising method to distinguish the protonated/deprotonated ions of the
metabolites from the adduct and fragment ions. </p>
In-Source CID Ramping (InCIDR) and Co-Variant Ion Analysis of Hydrophilic Interaction Chromatography (HILIC) Metabolomics
