title: Preferential alkali metal adduct formation by cis geometrical isomers of dicaffeoylquinic acids allows for efficient discrimination from their trans isomers during ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry.
abstract: BACKGROUND
  Caffeoylquinic acid (CQA) derivatives are a group of structurally diverse phytochemicals that have attracted attention due to their many health benefits. The structural diversity of these molecules is due in part to the presence of regio- and geometrical isomerism. This structural diversity hampers the accurate annotation of these molecules in plant extracts. Mass spectrometry (MS) is successfully used to differentiate between the different regioisomers of the CQA derivatives; however, the accurate discrimination of the geometrical isomers of these molecules has proven to be an elusive task.
  
  
  METHODS
  UV-irradiated methanolic solutions of diCQA were analyzed using an ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/QTOFMS) method in negative ionisation mode. An in-source collision-induced dissociation (ISCID) method was optimized by varying both the capillary and cone voltages to achieve differential fragmentation patterns between UV-generated geometrical isomers of the diCQAs during MS analyses.
  
  
  RESULTS
  Changes in the capillary voltage did not cause a significant difference to the fragmentation patterns of the four geometrical isomers, while changes in the cone voltage resulted in significant differences in the fragmentation patterns. The results also show, for the first time, the preferential formation of alkali metal (Li(+), Na(+) and K(+)) adducts by the cis geometrical isomers of diCQAs, compared to their trans counterparts.
  
  
  CONCLUSIONS
  Optimized QTOFMS-based methods may be used to differentiate the geometrical isomers of diCQAs. Finally, additives such as metal salts to induce adduct formation can be applied as an alternative method to differentiate closely related isomers which could have been difficult to differentiate under normal MS settings.
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Mpho M
authors.initials: MM
authors.lastname: Makola
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.|CSIR Biosciences, Natural Products and Agroprocessing Group, Pretoria, 0001, South Africa.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Steenkamp
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Dubery
authors.affiliation: Department of Chemistry, North-West University (Mafikeng Campus), Private Bag x2046, Mmabatho, 2735, South Africa.
authors.forename: Mwadham M
authors.initials: MM
authors.lastname: Kabanda
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Ntakadzeni E
authors.initials: NE
authors.lastname: Madala
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D007536:Isomerism; D013058:Mass Spectrometry / Q000379:methods*; D008672:Metals, Alkali / Q000737:chemistry*; D011801:Quinic Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry
chemical_list: D008672:Metals, Alkali; C472707:caffeoylquinic acid; D011801:Quinic Acid