Development of a LC-HRMS based approach to boost structural annotation of isomeric citrus flavanones

The structural annotation of target relies on high-resolution mass spectrometry (HRMS) information resulting in dubious identities in most cases. The accurate annotation of isomeric structures is still challenging to be confirmed with significant bottleneck.

This study focused on the improvement of structural annotation of candidate structures via four pairs of isomeric flavanone-7-O-diglucosides and their basic flavanone aglycones commonly detected in citrus products.

An integrated liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) approach merging retention time, accurate mass, tandem mass spectrometry (MS/MS) information (diagnostic ions), ion ratio at selected collision energy was established successfully.

Feasibility of this approach was validated confidently in biological samples with relative standard deviation (RSD) of ion ratio range from 3.91 to 12.28%. Differences of fragmentation patterns of citrus flavanones were illustrated reasonably. MS/MS fragments of (S)-hesperetin and (S)-isosakuranetin were complicated and showed typical radical ion [^1,2 A - H]^•- (m/z 164) in negative ESI mode due to the methoxyl group on B-ring, which showed huge difference with (R)-hesperetin and (R)-isosakuranetin.

This study integrated multiple levels to boost the confidence of structural annotation relied on LC-HRMS, and provided important values in practice for precise identification of citrus flavanones in biological matrices.