A fragmentation study of dihydroquercetin using triple quadrupole mass spectrometry and its application for identification of dihydroflavonols in Citrus juices.

A mass spectrometric method using electrospray ionization with triple quadrupole and quadrupole time-of-flight hybrid (Q-Tof) mass spectrometry has been applied to the structural characterization of dihydroflavonols. This family of compounds has been studied by liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the first time in this work. A comprehensive study of the product ion MS spectra of the [M+H](+) ion of a commercially available standard has been performed. The most useful fragmentations in terms of structural identification are those that involve cleavage of the C-ring, resulting in diagnostic ions of dihydroflavonol family: (1,3)A(0) (+), (1,2)B(0) (+), (1,2)B(0) (+)-CO, (0,2)A(0) (+), (0,2)A(0) (+)-H(2)O, (0,2)A(0) (+)-CO, and (0,2)A(0) (+)-H(2)O-CO, that allow the characterization of the substituents in the A- and B-rings. In addition to those ions, other product ions due to losses of H(2)O and CO molecules from the Y(0) (+) ion were observed. Their fragmentation mechanisms and ion structures have been proposed. The established fragmentation patterns have been used to successfully identity three dihydroflavonols found in tangerine juices for the first time.

Detection of non-coloured anthocyanin-flavanol derivatives in Rioja aged red wines by liquid chromatography-mass spectrometry.

Anthocyanins, responsible for wine colour, are involved in many reactions during wine ageing. Anthocyanin-flavanol associations give rise to derivatives in flavylium form that provide blue hues, but also derivatives that do not directly influence wine colour. These colourless derivatives remain mostly unknown but their roles during wine ageing are important for controlling wine quality. Colourless anthocyanin-flavanol derivatives formed during wine ageing have been studied in three aged red wines from Rioja using a combined method with Column Chromatography (CC) and High Performance Liquid Chromatography with Diode Array and Mass Spectrometric detections (HPLC-DADMS). Twenty-six compounds have been detected: 17 dimers with the anthocyanin in flavene form with possible anthocyanin-flavanol (type 1) and flavanol-anthocyanin (type 2) structures, and 9 with an A-type bicyclic anthocyanin-flavanol structure (type 3). Although some of malvidin derivatives have been previously reported, this is the first time that these derivatives (including different isomers) have also been detected for delphinidin, petunidin and peonidin.

On line characterization of 58 phenolic compounds in Citrus fruit juices from Spanish cultivars by high-performance liquid chromatography with photodiode-array detection coupled to electrospray ionization triple quadrupole mass spectrometry.

Polyphenol profile of Citrus juices of sweet orange, tangerine, lemon and grapefruit from Spanish cultivars was obtained by High-Performance Liquid Chromatography with Diode Array Detection coupled to Electrospray ionization and Triple Quadrupole Mass Spectrometry. Fifty eight phenolic compounds of five different classes were identified in these Citrus juices. Flavanone: O-dihexoside of naringenin; flavones: apigenin-7-O-rutinoside-4'-O-glucoside, luteolin-7-O-neohesperidoside-4'-O-glucoside, luteolin-6-C-glucoside, 6,8-di-C-acylhexosides of chrysoeriol and diosmetin, 6C- and 8C-glucoside-O-pentoside of apigenin, apigenin-6-C-hexoside-O-hexoside and apigenin-8-C-hexoside-O-acylrhamnoside; flavonols: 7-O-rutinosides of quercetin, kaempferol, isorhamnetin and tamarixetin, kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside-7-O-glucoside, tamarixetin-3-O-rutinoside-7-O-glucoside, isorhamnetin-3-O-hexoside-7-O-rhamnosylhexoside, 3-O-rhamnoside-7-O-rhamnosylhexoside of quercetin and isorhamnetin and kaempferol-3-O-rhamnosylhexoside-7-O-rhamnoside; hydroxycinnamic acids: O-hexoside of ferulic and sinapic acid; and, coumarins: O-hexoside and O-rhamnosylhexoside of scopoletin, had not previously been reported in Citrus juices to our knowledge. Structures have been assigned on the basis of the complementary information obtained from retention time, UV-visible spectra, scan mode MS spectra, and fragmentation patterns in MS(2) spectra obtained using different collision energies. A structure diagnosis scheme is provided for the identification of different phenolic compounds.

Chemometric characterization of fruit juices from Spanish cultivars according to their phenolic compound contents: I. Citrus fruits.

The data set composed by phenolic compound profiles of 83 Citrus juices (determined by HPLC-DAD-MS/MS) was evaluated by chemometrics to differentiate them according to Citrus species (sweet orange, tangerine, lemon, and grapefruit). Cluster analysis (CA) and principal component analysis (PCA) showed natural sample grouping among Citrus species and even the Citrus subclass. Most of the information contained in the full data set can be captured if only 15 phenolic compounds (concentration ≥10 mg/L), which can be quantified with fast and accurate methods in real samples, are introduced in the models; a good classification which allows the confirmation of the authenticity of juices is achieved by linear discriminant analysis. Using this reduced data set, fast and routine methods have been developed for predicting the percentage of grapefruit in adulterated sweet orange juices using principal component regression (PCR) and partial least-squares regression (PLS). The PLS model has provided suitable estimation errors.

A general analytical strategy for the characterization of phenolic compounds in fruit juices by high-performance liquid chromatography with diode array detection coupled to electrospray ionization and triple quadrupole mass spectrometry.

In the present study, a methodology based on liquid chromatography with diode array detection (HPLC/DAD) coupled to an electrospray ionization (ESI) interface and a triple quadrupole mass spectrometer for the simultaneous identification of phenolic compounds in fruit juices has been developed. 72 available phenolic compound standards from diverse families present in fruits have been studied in order to analyze their fragmentation pattern. As a result, a general strategy for the characterization of unknown phenolic compounds in fruit juices was designed: (i) taking into account its UV-visible spectrum and elution order, assign the unknown polyphenol to a polyphenol class, (ii) identify the quasi-molecular ion using positive and negative MS spectra, being supported by adducts generated with solvent or sodium and molecular complexes, (iii) determinate the pattern of glycosylation in positive mode using ESI(+)-CID MS/MS product ion scan experiments, selecting the quasi-molecular ion as precursor ion, and finally, (iv) study the identity of the aglycone through ESI(+)-CID MS/MS product ion spectra from the protonated aglycone, [Y(0)](+). This strategy was successfully employed for the characterization of known and unknown phenolic compounds in juices from 17 different fruits.

New features on the fragmentation and differentiation of C-glycosidic flavone isomers by positive electrospray ionization and triple quadrupole mass spectrometry.

Six flavone mono-C-glucosides, four standards (beta-D-glucopyranosyl-(1 --> C-6)- and -(1 --> C-8)- apigenin and luteolin) and two others from lemon juice (beta-D-glucopyranosyl-(1 --> C-6)- and -(1 --> C-8)-diosmetin) have been studied in order to analyze their fragmentation patterns. Initial separation was carried out using high-performance liquid chromatography with diode-array detection (HPLC/DAD) coupled to an electrospray ionization (ESI) interface and a triple quadrupole mass spectrometer. Several systematic differences between collision-induced dissociation tandem mass (CID-MS/MS) spectra of C-6- and C-8-isomers have been found and some general guidelines and two new diagnostic product ions have been proposed for the differentiation of C-6- and C-8-flavonoid glycosides. These results have been successfully applied to the characterization of two flavone C-glycosides found in lemon juice, and mass spectra of a flavone di-C-glycoside detected in lemon juice have been studied and interpreted.