Separation of phenolics

General conditions for separation of phenols 30 m DB-5 column, 80-150° at 87min. 

Monde, T., Kamiusuki, T., Kuroda, T., Mikumo, K., Ohkawa, T., and Fukube, H., High-performance liquid chromatographic separation of phenols on a fluorocarbon-bonded silica gel column, /. Chromatogr. A, 722, 273, 1996. 

M.A. Hawryl, A. Hawryl and E. Sochewinski, Application of normal- and reversed-phase 2D TLC on a cyanopropyl-bonded polar stationary phase for separation of phenolic compounds from the flowers of Sambucus nigra L. J. Planar Chromatogr.-Mod. TLC 15 (2002) 4-10. 

The TLC analysis of flavonoids was performed not only in the extract of medicinal plants and model mixtures but also in various other matrices. Thus, phenolic compounds in red wines have also been determined by TLC. Wine samples were acidified to pH 2.0 with 0.1 M HC1 and 25 ml of acidified wine was extracted with 2 X 25 ml of diethyl ether. The organic phase was evaporated to dryness and redissolved in 5.0 ml of methanol. Separation of phenolic compounds was performed on silica layers using 11 different mobile phases. In order to find the best separation system, information theory and cluster analysis was applied. The RF values determined in 11 mobile phases are compiled in Table 2.45. 

Capillary columns may provide the best method for the separation of phenols prior to their quantification (Eichelberger et al. 1983 Shafer et al. 1981 Sithole et al. 1986). Of the various methods available for detection, the two commonly used methods that are most sensitive are mass spectrometry and flame ionization detection. Although electron capture detectors provide good sensitivities for higher chlorine-substituted phenols, they are poor for phenol itself (Sithole et al. 1986). The best method for the quantification of phenol may be mass spectrometric detection in the selected ion mode, but the loss of qualitative information may be significant (Eichelberger et al. 1983). 

High-performance liquid chromatography (HPLC) techniques are widely used for separation of phenolic compounds. Both reverse- and normal-phase HPLC methods have been used to separate and quantify PAs but have enjoyed only limited success. In reverse-phase HPLC, PAs smaller than trimers are well separated, while higher oligomers and polymers are co-eluted as a broad unresolved peak [8,13,37]. For our reverse-phase analyses, HPLC separation was achieved using a reverse phase. Cl8, 5 (Jtm 4.6 X 250 mm column (J. T. Baker, http //www.mallbaker.com/). Samples were eluted with a water/acetonitrile gradient, 95 5 to 30 70 in 65 min, at a flow rate of 0.8 mL/min. The water was adjusted with acetic acid to a final concentration of 0.1%. All mass spectra were acquired using a Bruker Esquire LC-MS equipped with an electrospray ionization source in the positive mode. 

Among the numerous applications of SPE are separations of phenolic acids and flavonoids from wines and fruit juices. Sep-Pak Cig cartridges have been used for the fractionation of flavonol glycosides and phenolic compounds from cranberry juice into neutral and acidic parts before HPLC analysis. Antimutagenic flavonoids were identified in aqueous extracts of dry spinach after removal of lipophilic compounds by SPE. ... 

Slimestad, R., Marston, A., and Hostettmann, K., Preparative separation of phenolic compounds from Picea abies by high-speed countercurrent chromatography, J. Chromatogr. A, 719, 438, 1996. 

In the last years, ILs have been applied as matrices for matrix-assisted laser desorption/ionization (MALDI) MS [42], thus expanding the use of MALDI. In Ref. 38 the suitability of alkylammonium- and alkylimidazolium salts of a-cyano-4-hydroxycinnamic acid was investigated as a MALDI matrix and at the same time as the additive of BGE. The alkylammonium salt produced better separation of phenolic compounds than the alkylimidazolium salt. The investigation suggests that it is possible to synthesize ILs suitable for electrophoretic analysis as well as for online MALDI-MS analysis. 

Yanes and coworkers [43] demonstrated an application of IL for aqueous CE for fhe separation of phenolic compounds (flavonoids) found in grape seed exfracfs. By using [C Qlm] (n = 2,4) ILs as additives for the running electrolyte, a simple and reproducible electrophoretic method for the separation of polyphenols was developed. If was speculated that the separation mechanism was based on an association between the imidazolium cations and the polyphenols. The role of fhe alkyl substituents on the imidazolium cations was investigated and discussed [43]. The anion has little effect on the separation while a related study demonstrated that interaction between phenolic compounds and the IL cations in water occurred through n-n interactions. 

Kuldvee, R., Vaher, M., Koel, M., and Kaljurand, M., Heteroconjugation-based capillary elctrophoretic separation of phenolic compounds in acetonitrile and propylene carbonate. Electrophoresis, 24,1627-1634, 2003. 

Several gas chromatographic separations of phenols from plasticizers have been accomplished. Dinonyl phthalate (25) or silicone oil (20) are recommended as column materials. Saponification is best carried out in glycolic potassium hydroxide, which, for example, saponifies tricresyl phosphate quantitatively. 

Reversed-phase chromatography is the most popular mode of analytical liquid chromatography for phenolic compounds. In most cases, the reported systems for the separation of phenolics and their glycosides in foods are carried out on reversed-phase chromatography on silica-based Cl8 bonded-phase columns. Occasionally, silica columns bonded with C8 were applied in the analysis of phenolic acid standards and coumarins (7), and C6 columns for the analysis of ferulic acid in wheat straw (8). 

Fig. 8 HPLC separation of phenolics and HMF from apple juice.

G Marko-Varga, D Barcelo. Liquid chromatographic retention and separation of phenols and related aromatic compounds on reversed phase columns. Chromatographia 34 146-154, 1992. 

A common, simple, inexpensive and relatively fast method for the separation of phenolic compounds from a mixture is thin layer chromatography (TLC). A small amount of the extract (40-100 pi) is applied approximately 2 cm from the bottom of a thin layer chromatography... 

T. Matsuura and S. Sourirajan, Reverse Osmosis Separation of Phenols in Aqueous Solutions Using Porous Cellulose Acetate Membranes, J. Appl. Polym. Sci. 15, 2531 (1972). 

Shen, S., Z. Chang, and H. Liu. 2006. Three-liquid-phase extraction systems for separation of phenol and p-nitrophenol from wastewater. Sep. Purif. Technol. 49 217-222. 

In particular, our research is addressed to the simultaneous one-step production and separation of phenol by selective oxidation of benzene in a membrane photoreactor using Ti02 as catalyst and a membrane contactor for the separation process. 

The data obtained in a first set of experiments have shown a good separation of phenol from the reaction environment (Figure 15.3), although also other oxidation products passed through the membrane. 

E. Burtschen, H. Binder, R. Concin, and O. Bobleter, Separation of phenols, phenolic aldehydes, ketones, and acids by HPLC, J. Chromatogr., 252 161 (1982). 

Acetates of fatty [1] and polyhydric [2] alcohols, phenols [3] and chlorophenols [4] have been studied. Fell and Lee [3] described a GC method for the determination of polyhydric phenols in urine, which, having been extracted, were acetylated with acetic anhydride in the presence of 4-dimethylaminopyridine. According to these authors this substance shows much stronger catalytic effects than does the usually used pyridine. The derivatives are formed rapidly and quantitatively even in very dilute solutions. In the absence of the catalyst, bifunctional phenols provide more than one GC peak. Slightly polar OV-210 is recommended for the separation of phenol acetates, but analysis on nonpolar OV-101 leads to tailing, probably as a consequence of insufficient deactivation of the column. 

FIGURE 5-19. Separation of phenolic acids using the ion suppression technique. Mobile phase 5% acetic acid in water. (Chromatogram reprinted from L. W. Wulf and C. W. Nagel, J. Chromatography, 116, 271 (1976) with permission.)... 

Ionic organic compounds are often water soluble while the unionized forms will be less water soluble. Because of this, ion suppression is commonly used to enhance the separation of organic acids. A typical example of the use of ion suppression is for the separation of phenolic acids shown in Figure 5-19. Without the addition of acetic acid to the eluent the acids would have eluted as broadly tailed peaks with little retention. 

Figure 4. HPLC separation of phenolic components of an aqueous leachate from the surface of corn leaves infected with Colletotrichum graminicola. a) untreated leachate b) base hydrolyzed leachate c) acid hydrolyzed leachate. Compounds 1 and 2 are isomers of p-coumaric acid. Compounds separated isocratically on a reversed phase C-18 column with a 70 % to 30 % mixture of absolute methanol and 1 % acetic acid. Reproduced with permission from Ref. 69. Copyright 1989 Academic Press, Inc.

Cacciola F. Jandera P. Mondello L. 2007. Comparison of high-temperature gradient heart-cutting and comprehensive LC x LC systems for the separation of phenolic antioxidants. Chromatographia 66 661 667. 

Jandera P. Vynuchalova K. Hajek T. Cesla P. Vohralik G. 2008. Characterization of HPLC eolumns for two-dimensional LCxLC separations of phenolic acids and flavonoids. J. Chemometrics 22 203-217. 

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