Antioxidant mobile phenols

Figure 5.9 Thin-layer chromatograms of mixtures of antioxidants. Mobile phase benzene - ethyl acetate - acetone (100 5 2). Columns are (a) phenols, (b) amines, (c) hydroquinones, (d) miscellaneous antioxidants, and (e) mixtures of unknown extract formulations Reproduced from Simpson and Currell, RSC [32]...

McCue, P.P. and Shetty, K. 2005. Phenolic antioxidant mobilization during yogurt production from soymilk using Kefir euttures. Process Biochemistry, 4(fifi), 1791 1797. 

It has been observed that complete immobilisation of the stabiliser through a graft leads to deactivation. However, proper selection of the ratio of phenolic to graftable groups leads to a polymer-bound product which retains sufficient mobility to provide a high level of antioxidant activity. An n/m ratio of 5-10 provides an optimal balance of graftability and antioxidant activity [144]. 

After benzoylation, it was possible to analyze together the food substances of varying chemical structures, such as alcohols, esters of 4-hydroxybenzoic acid, phenolic antioxidants, saccharides, and sugar alcohols. The method allowed the determination of these substances in different matrices by the same analytical procedure, using the same cleanup. The preservatives were separated on an RP-18 column. Acetonitrile-water (50 35) or acetonitrile-water-butylmethyl ether (110 35 40) were used as mobile phases. Detection was UV at 230 nm (71). 

The mobile phases used in normal-phase chromatography are based on nonpolar hydrocarbons, such as hexane, heptane, or octane, to which is added a small amount of a more polar solvent, such as 2-propanol.5 Solvent selectivity is controlled by the nature of the added solvent. Additives with large dipole moments, such as methylene chloride and 1,2-dichlor-oethane, interact preferentially with solutes that have large dipole moments, such as nitro- compounds, nitriles, amines, and sulfoxides. Good proton donors such as chloroform, m-cresol, and water interact preferentially with basic solutes such as amines and sulfoxides, whereas good proton acceptors such as alcohols, ethers, and amines tend to interact best with hydroxylated molecules such as acids and phenols. A variety of solvents used as mobile phases in normal-phase chromatography are listed in Table 2.2, some of which may need to be stabilized by addition of an antioxidant, such as 3-5% ethanol, because of the propensity for peroxide formation. 

Mobile phases in RPC x RPC are usually compatible in terms of miscibility however, big differences in the viscosities of the employed mobile phases may lead to flow instability at the mixing interface and should be therefore avoided.75 Nevertheless, RPC x RPC can be performed when the mobile phase/stationary phases employed in the first and second dimension have considerable selectivity differences, as shown for phenolic antioxidants.76... 

The presence in drinking water of phenol, cresol and various antioxidants (109-113) used for synthetic rubber preservation was tested by SPE with a Cig cartridge followed by RP-HPLC on a Cig column with UVD at 280 nm °. An automatic LC system was devised for determination of trace amounts of phenols in water, based on SPE preconcentration, RP microcolumns, isocratic methanol-water mobile phase and ELD in the autoincrement mode. LOD was 40-600 ngL, for eleven priority phenols . ... 

Figure 18.10 Two-dimensional separation of a mixture of phenolic and flavone antioxidants [after P. Jandera, University of Pardubice, Czech Republic see also F. Cacciola et a ., J. Chromatogr. A, 1149, 73 (2007)]. Conditions in the first dimension column, 15 cm x 4.6 mm i.d. stationary phase, PEG silica 5 pm mobile phase, 0.3 ml min" water-acetonitrile, gradient 1-55% acetonitrile in 200 min. Interface ten-port valve with two storage columns X-Terra Cl8 2.5 pm, 3 cm x 4.6 mm i.d. which concentrate the eluate. Cycle time, 5 min. Conditions in the second dimension column, 10 cm x 4.6 mm i.d. stationary phase, SpeedROD RP-18e (monolith) mobile phase, 2 ml min" water-acetonitrile, gradient 1-40% acetonitrile in 5min. Diode array detector with 254 + 260 + 280 + 320 nm. Of the numerous identified analytes only the most important ones are specified in the figure.

Irradiation of PP in air leads to oxidative degradation, evidenced by discoloration and embrittlement. The extent of the degradation depends on crystallinity, MW, MWD, and chain mobility [Kadir et al., 1989 Kashiwabara and Seguchi, 1992 Williams, 1992]. Neat PP does not discolor on irradiation up to 100 kGy [Williams, 1992]. The antioxidants should be selected so as not to cause the discoloration. However, most commercial preparations containing phenolic antioxidants turn yellow on irradiation. Phenolic antioxidants produce stable phenoxyl radicals that convert into colored quinonoids. Other stabilizers and antioxidants are compounds that contain either phosphorous [Bentrude, 1965 de Paolo and Smith, 1968], sulfur [Jirackova and Pospisil, 1979], or hindered piperidine derivatives [Carlsson, et al., 1980 Felder et al., 1980 Allen et al., 1981]. A comprehensive list of stabilizers and their mode of action was given by Dexter [1992]. It is noteworthy that antioxidants and stabilizers are excluded from the crystalline regions [Winslow et al., 1966] thus they would provide protection only within the amorphous domains. 

Primary antioxidants are mono- or poly-hydroxy phenols with various ring substitutions including synthetic (BHA, BHT, PG), and natural compounds (tocopherols, carotenoids). Their antioxidant potency is determined by several factors, including chemical reactivity of the antioxidant toward the radical, concentration and mobility of the antioxidant in the microenvironment, and interaction with other antioxidants. ... 

Table 6.2 Paper chromatographic separation of phenolic antioxidants Acetylated paper. Mobile phase (1) Butyl acetate - pyridine - methanol - water (1 5 1 3) (2) Isopropanol - methanol - water (3 3 3) Spray reagents (1) Tollen s reagent (2) Millon s reagent ...

Single phenol and bisphenol antioxidants, such as butyl-ated hydroxytoluene (BHT), 2246, and bisphenol A, because of their lower molecular weight and high volatility and mobility, can color plastics easily therefore their use in plastics has recently declined greatly. Polyphenollc antioxidants 1010 and 1070 are the leading plastic antioxidant products in the world. 1010 is the best plastic antioxidant because of its high... 

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