Thin layer chromatography antioxidants

Antioxidants (qv) have a positive effect on oils when present in the proper concentration. Sterols and tocopherols, which are natural antioxidants, may be analy2ed by gas-Hquid chromatography (glc), high performance Hquid chromatography (hplc), or thin-layer chromatography (tic). Synthetic antioxidants maybe added by processors to improve the performance or shelf life of products. These compounds include butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), / fZ-butyUiydroquinone (TBHQ), and propyl gallate. These materials may likewise be analy2ed by glc, hplc, or tic. Citric acid (qv), which functions as a metal chelator, may also be deterrnined by glc. 

CH van Peteghem, DA Dekeyser. Systematic identification of antioxidants in lards, shortenings, and vegetable oils by thin layer chromatography. J Assoc Off Anal Chem 64 1331-1335, 1981. 

The products, which were obtained as viscous, pale amber oils, were purified by vacuum distillation or molecular distillation, whichever was best suited to the particular product. The yield of dialkylated p-cresol was 85-95%. Freedom from appreciable amounts of monoalkylated product was established by vapor phase chromatography (VPC), thin-layer chromatography (TLC), and molecular weight determination. The products obtained from propylene trimer and tetramer had no appreciable antioxidant activity) and will not be considered further here. 

A simpler, lower cost technique which can readily separate the antioxidants from plastic extracts and give a qualitative analysis is thin layer chromatography (BS6630, 1985). In thin layer chromatography (TLC), the stationary phase is comprised of a thin layer of adsorbent such as cellulose, alumina, or silica gel on a plastic sheet, thick aluminium foil, or a glass plate. A small spot of solution containing the sample is applied to a plate, about 1 cm from the base. The plate is then placed in a sealed container which holds a suitable solvent, such as ethanol, so that it does not come into contact with the spots. The solvent moves up the plate by capillary action and meets the sample mixture, which is dissolved and is carried up the plate by the solvent. Components in the sample mixture travel at different rates due to differences in solubility in the solvent, and due to differences in their attraction to the plate. 

It is well known that the phenol groups (which are bonded to the aporphine ring) and the benzylic amine function are responsible for the antioxidant and free radical scavenging activities of boldine [60], In addition, the presence of hydroxyl moieties in the chemical skeleton of boldine is responsible for its lipid peroxidation inhibitory activity [61], The level of boldine in the bark of boldo is more than 6% [62], Paper electrophoresis, voltammetric method, thin-layer chromatography and gas chromatography are common analytical methods for boldine determination [63],... 

Table 10.12. Relative effectiveness of antioxidants in lecithin liposomes versus polarity by thin-layer chromatography (TLC) ...

These workers point out that usually the additive must be separated in a pure state from co-extracted additives usually by thin-layer chromatography (TLC) and then identified by measurement of the UV, IR, nuclear magnetic resonance (NMR) and mass spectra of the compound. This full treatment is required only for new stabilisers - for a characterisation of well known compounds the simplest method is by direct comparison of the UV absorption spectra with those of a series of known stabilisers. For some compounds this will probably be sufficient, but many substituted phenols have similar spectra, and for three of the most frequently used antioxidants the UV spectra are identical. Topanol OC, lonox 330 and Binox M (see Table 2.11 for their chemical constitution) in ethanolic solution all have = 277 nm, with a shoulder at 282 nm. To extend this procedure Ruddle andWilson [66] prepared the spectra of alkaline solutions of the phenols, which were then measured either directly against a solvent blank or as difference spectra measured against the neutral solution. This still gives almost identical spectra for the three compounds mentioned previously. 

Figure 5.2 Thin-layer chromatography of antioxidants. Three phenolic antioxidants developed with dichlorobenzoquinone chlorimine spray reagent (2 6)...

Figure 5.12 Separation of amine antioxidants and antiozonants by one-dimensional thin-layer chromatography. Solvent benzene - acetone - concentrated ammonium hydroxide (100 5 0.1) development distance 15 cm indicator 4% benzoyl peroxide in benzene. 1 = N-phenyl-l-naphthylamine 2 = N-phenyl-2-naphthylamine 3 = p-(p-tolylsulfonylamido)-diphenylamine 4 = nonylated diphenylamines 5 = octylated diphenylamines 6 = octylated diphenylamines 7 = octylated diphenylamines 8 = 4,4-dimethoxydiphenylamine 9 = 4-isopropoxydiphenylamine 10 = 4"-isopropyl-aminodiphenylamine 11 = N, N-diisopropyl-p-phenylenediamine 12 = N,N -6i-sec-h xtyi-p-p)Lieny emdizTmne. Reproduced from [119]...

Figure 5.13 Separation of phenolic antioxidants by thin-layer chromatography. Solvent benzene development distance 15 cm indicators (a) borate buffer (b) 0.1% 2,6-dichloro quinonechlorimide in methanol. 1 = hydroquinone monobenzyl ether 2 = 2,6-di-rerr-butyl-phenol 3 = 2,6-di-tert-butyl-4-methyl-phenol 4 = 2,6-di-tcrt-butyl-a-methoxy-4-methyl-phenol 5 = 2-a-methyl-cyclohexyl-4, 6-dimethyl-phenol 6 = butylated hydroxyanisole 7 = butylated hydroxy toluene 8 = 4,4"-bis (2,6-di-terf-butyl-phenol) 9 = 2,2"-methylene-bis (4-methyl-6-terf-butyl-phenol) 10 = 2,2"-methylene-bis (4-ethyl-6-fert-butyl-phenol) Reproduced from Kreiner and Warner, Journal of Chromatography [119]...

Polyolefins Aqueous, alcoholic, oily Dilaurythiodipropionate secondary antioxidant Thin-layer chromatography a... 

Plastics utensils Sunflower seed oil Santonox R antioxidant (4,4 thio-f /s-6-tert butyl-w-cresol) Thin-layer chromatography [149, 150]... 

Methanol-water (90 10 v/v) extracts of five polar lichen species, namely, Stereocaulon alpinum, Ramalina terebrata, Caloplaca sp., Lecanora sp. and Caloplaca regalis, from King George Island were analysed using thin layer chromatography (TLC) followed by a DPPH (2,2-diphenyl-l-picrylhydrazyl) spray technique. The experimental data showed that 33-50 % of the major crmstituents of the test extracts were active antioxidants (Bhattarai et aL 2008a, b). 

Bhattarai HD, Paudel B, Hong SG et al (2008) Thin-layer chromatography analysis of antioxidant constituents of lichens from Antarctica. J Nat Med 62 481-484... 

Generally, methods are based on solvent extraction of the additive followed by analysis for the extracted additive by a suitable physical technique such as visible spectrophotometry of the coupled antioxidant, redox spectrophotometric methods, ultraviolet spectroscopy, infrared spectroscopy, gas chromatography, thin-layer chromatography or column chromatography. In general, direct chemical methods of analysis have not foimd favour. These include potentiometric titration with standard sodium isopropoxide in pyridine medium or reaction of the antioxidant with excess standard potassium bromide-potassium bromate (ie. free bromine) and estimation of the unused bromine by addition of potassium iodide and determination of the iodine produced by titration with sodium thiosulphate to the starch end-point. ... 

Dobies has described detailed thin-layer procedures for determining 0.02 - 0.2% of various antioxidants in polyethylene and polypropylene films (method 10). Simpson and Currell use thin-layer chromatography in the determination of additives such as... 

Methods 17 and 18, respectively, determine Cyasorb UV 531 (2-hydroxy-4-n-octoxybenzophenone) in polyolefins by direct infrared spectroscopy and thin-layer chromatography. Phenolic and organophosphorus type antioxidants do not interfere in these procedures. Method 19 describes an ultraviolet spectroscopic method for the determination of Tinuvin 326 ultraviolet absorber in polypropylene. 

Procedures involving solvent extraction followed by thin-layer chromatography have been described for the determination of phenolic and amine types of antioxidants and optical whiteners in PVC. 

Auler, J., Identification of Antioxidants, Antiozonants and Accelerators by means of Thin-layer Chromatography ETDC Aachen, Materials and Research Dept., (1967)... 

Some typical applications of thin-layer chromatography to the determination of one type of additive, namely antioxidants, in polymers are tabulated in Table 5.5 (Rf values) and Table 5.6. 

METHOD 9 - DETERMINATION OF SANTONOX R PHENOLIC ANTIOXIDANT IN POLYOLEFINS. THIN LAYER CHROMATOGRAPHY. 

METHOD 41 - IDENTIFICATION OF ACCELERATORS AND ANTIOXIDANTS IN NON-VULCANIZED RUBBER COMPOUNDS. THIN LAYER CHROMATOGRAPHY. ... 

Determination of Santonox R phenolic antioxidant in polyolefins. Thin layer chromatography... 

Uhde and co-workers [34, 35] have studied the migration of 4,4 -thiobis-6-tert-butyl-w-cresol (Santonex R) from plastics utensils into sunflower seed oil. Sunflower seed oil that had been stored in vessels of polyethylene containing this antioxidant was diluted (3 5) with pentane and extracted with acetonitrile containing 5 % of water. The concentrated acetonitrile extract (or an ethanol solution of the residue on evaporation) was snbjected to thin-layer chromatography on Kieselgel with hexane-ethyl acetate (10 3) as solvent. To detect the antioxidant (down to 0.1 ppm) the plate was sprayed with 3,5-dichloro-p-benzoquinonechlorimine solution. To determine the antioxidant, the zone at Rf = 0.44 (located by means of iodine vapour) was removed and treated with fuming nitric acid sulfuric acid (1 1). The nitro-derivative of the antioxidant was determined in the product by polarography after the addition of urea and sodium acetate [35],... 

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