Flavonoids solid-phase extraction

As well as typical sample preparation methods such as filtration and liquid-liquid extraction, newer developments are now extensively used. The first of these is solid-phase extraction (SPE). This is a rapid, economical, and sensitive technique that uses several different types of cartridges and disks, with a variety of sorbents. Sample preparation and concentration can be achieved in a single step. Interfering sugars can be eluted with aqueous methanol on reversed-phase columns prior to elution of flavonoids with methanol. 

A methodological approach for an effective and reliable quality control of Chinese star anise [I. verum Hook. F.) was developed and validated by Lederer et al. (2006). A combined method of TLC and HPLC-MS/MS was used for differentiation ofvarious Ulicium species, especially Chinese and Japanese star anise. Species can be distinguished by their TLC flavonoid pattern. A sensitive and selective HPLC/ESI-MS/MS method was developed for the detection and quantification of lower admixtures of I. anisatum and of further toxic Ulicium species at a low concentration range using the sesquiterpene, lactone anisatin, as a marker. This assay includes a solid-phase extraction clean-up procedure with a high recovery (> 90%). 

Weiss, R. Molinelli, A. Jakusch, M. Mizaikoff, B. 2001. Molecular imprinting and solid phase extraction of flavonoid compounds. Bioseparation 10 379-387. Wender, S.H. Gage,T.B. 1949. Paper chromatography of flavonoid pigments. Science 109 287-289. 

Stationary phases (silica, reversed phases, Amberlite, and Sephadex) or by solid-phase extraction techniques using different adsorbents, which in the last decade has been found very convenient for the isolation of flavonoids from complex matrices. 

An HPLC-DAD method was developed for the separation and the determination of flavonoid and phenolic antioxidants in commercial and freshly prepared cranberry juice.Two sample preparation procedures were used with and without hydrolysis of the glycoside forms of flavonoids carried out by the addition of HCl in the step prior to solid-phase extraction (SPE). The flavonoid and phenolic compounds were then fractionated into neutral and acidic groups via a solid-phase extraction method (Sep-Pak Cig), followed by a RP HPLC separation with gradient elution with water-methanol-acetic acid and a detection at 280 and 360 nm. A comparison of the chromatograms obtained for extracts prepared with and without hydrolysis showed that flavonoids and phenolic acids exist predominantly in combined forms such as glycosides and esters. In a freshly squeezed cranberry juice, for instance, 400 mg of total flavonoids and phenolics per liter of sample was found, 56% of which were flavonoids. Quercetin was the main flavonoid in the hydrolyzed products, where it accounted for about 75% of the total flavonoids, while it was absent in the unhydrolyzed products. 

Most of the extraction techniques of phenolic compounds from vegetables are based on ultrasound-assisted extraction (UAE) [27,44,45], In addition, other techniques have been successfully applied to the pretreatment of phenolic compounds in fruits and vegetables, including pressurized liquid extraction (PLE) [46], solid-phase extraction (SPE) [47], supercritical fluid extraction (SFE) [48], microwave-assisted extraction (MAE) [49], rotary shaker-assisted extraction (RAE), [50] and QuEChERS (acronym of quick, easy, cheap, effective, rugged and safe) [51], as can be observed in Tables 16.3 and 16.4. In some cases, an acid treatment [52] was applied to hydrolyze the glycosides in order to determine the content of free and conjugated flavonoids as aglycons. 

Liquid-liquid extraction (LLE) and solid-phase extraction (SPE) are usually performed on liquid samples, such as beverages or biological fluids. These two extraction methods are used to concentrate flavonoid analytes based oti their solubility in different solvents and their polarity. Unwanted lipids or lipophilic materials in crude extract can be eliminated by washing it with nonpolar solvents, such as hexane or dichloromethane. 

HPLC-UV-NMR is a powerful technique for the identification and characterization of flavonoids. However, there are drawbacks, as NMR remains rather insensitive because of the need for solvent suppression, which has restricted the observable NMR range. Recently, two major research developments in HPLC-UV-NMR are post-column solid-phase extraction (HPLC-UV-SPE-NMR) and combination of HPLC-UV-SPE with capillary separations and NMR detection [89]. A post-column treatment of analyte focusing and multiple trapping through a SPE has solved the problem of sensitivity and solvent suppression. The separation and elucidation of three C-methylated flavanones and five dihydrochalcones from Myrica gale seeds have been achieved by HPLC-DAD-SPE-NMR and... 

Aberham A, Cicek SS, Schneider P, Stuppner H (2010) Analysis of sesquiterpene lactones, lignans, and flavonoids in wormwood (Artemisia absinthium 1.) using high-performance liquid chromatography (HPLC)-mass spectrometry, reversed phase HPLC, and HPLC-solid phase extraction-nuclear magnetic resonance. J Agric Food Chem 58 10817-10823... 

HPLC is the method of choice to accurately determine both the composition and the absolute concentrations of the flavonoids in a given sample. Since HPLC was first described for use in flavonoid determination by Fisher and Wheaton (1976), its use has been expanded and improved to evalute flavonoids in extracts from fruit tissues, leaves, stems, roots, floral parts and juice. Extraction procedures are similar to those used in preparing samples for TLC, except that non-evaporating solvents such as dimethylsulphoxide and dimethylformamide can be utilized, which are excellent solvents for most of the flavonoids. Sample preparation can be a complex series of steps that includes some solid phase preparative separations or as simple as extraction, filtration and injection. 

Other methods, such as matrix solid-phase dispersion (MSPD) have also been applied in sample pretreatment. Among other applications, MSPD was recently used for the analysis of seven flavonoids in citrus juice [56] or 18 flavonoids from Ginkgo biloba tablets combining extraction and cleanup in a single run [57]. 

Barfi, B., A. Asghari, M. Rajabi, A. Barfi, and I. Saeidi. 2013. Simplified miniaturized ultrasound-assisted matrix solid phase dispersion extraction and high performance liquid chromatographic determination of seven flavonoids in citrus fruit juice and human fluid samples Hesperetin and naringenin as biomarkers, f. Chromatogr. A 13H(l) 30-40. 

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