Antioxidants quantitative determination

Kellum [115] has described a class-selective oxidation chemistry procedure for the quantitative determination of secondary antioxidants in extracts of PE and PP with great precision (better than 1 %). Diorgano sulfides and tertiary phosphites can be quantitatively oxidised with /-chloropcroxybenzoic acid to the corresponding sulfones and phosphates with no interference from other stabilisers or additives. Hindered phenols, benzophenones, triazoles, fatty acid amides, and stearate... 

Kim el al. [582] have described maleimide-based antioxidants melt grafted onto low-MW PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Smedberg el al. [583] have characterised polymer-bound stabilisers by FTIR and NMR. The binding of antioxidants and photostabilisers to polyurethanes was verified by tJV/VIS spectroscopy [584]. 

GC is extensively used to determine phenolic and amine antioxidants, UV light absorbers, stabilisers and organic peroxide residues, in particular in polyolefins, polystyrene and rubbers (cf. Table 61 of Crompton [158]). Ostromow [159] has described the quantitative determination of stabilisers and AOs in acetone or methanol extracts of rubbers and elastomers by means of GC. The method is restricted to analytes which volatilise between 160 °C and 300 °C without decomposition. A selection of 47 reports on GC analysis of AOs in elastomers (period 1959-1982) has been published... 

David et al. [184] have shown that cool on-column injection and the use of deactivated thermally stable columns in CGC-FID and CGC-F1D-MS for quantitative determination of additives (antistatics, antifogging agents, UV and light stabilisers, antioxidants, etc.) in mixtures prevents thermal degradation of high-MW compounds. Perkins et al. [101] have reported development of an analysis method for 100 ppm polymer additives in a 500 p,L SEC fraction in DCM by means of at-column GC (total elution time 27 min repeatability 3-7 %). Requirements for the method were (i) on-line (ii) use of whole fraction (LVI) and (iii) determination of high-MW compounds (1200 Da) at low concentrations. Difficult matrix introduction (DMI) and selective extraction can be used for GC analysis of silicone oil contamination in paints and other complex analytical problems. 

JV/VIS spectrophotometry was the earliest technique to determine antioxidants [37-39]. UV/VIS has been used for the quantitative determination of BHT, stalite, etc. in rubbers [40]. Quantitative UV spectrophotometric... 

Composition and structure of newly developed additives are commonly examined by IR, NMR, MS and elemental analysis, e.g. recently developed higher MW antioxidants [115]. Infrared spectroscopy is also well suited to the direct verification of compound composition and quantitative determination of additives in polymers. Gray and Neri [116] have used Soxhlet... 

Tea (Camellia sinensis) is one of the most frequently consumed beverages in the world and, consequently, an important agricultural product [168], It has been proved many times that tea may reduce cholesterol level, hypertension, and shows antioxidant and anti-microbial effects [169], Because of its importance, a considerable number of analytical methods have been developed for the separation and quantitative determination of the constituents of tea [170,171]. Thus, the application of high-speed counter-current chromatography [172,173], and HPLC-APCI-MS [174] have been reported. 

Francis, V.C. Sharma, Y.N. Bhardwaj, I.S. Quantitative determination of antioxidants and ultraviolet stabilizers in polymer by high performance liquid chromatography. Angew. Makromol. Chem. 1983, 113, 219-225. 

Nakatani N., Kayano S., Kikuzaki, H, Sumino, K, Katagiri, K., and Mitani, T., Identification, quantitative determination and antioxidative activities of chlorogenic acid isomers in prune Prunus domestica L.). J. Agric. Food Chem., 48, 5512-5516, 2000. 

Identification, Quantitative Determination, and Antioxidant Properties of Polyphenols of Some Malian Medicinal Plant Parts... 

For quantitative determination of the concentrations of antioxidants in PP that are required for the analysis of diffusion data, an isothermal DTA technique was developed that directly uses the effect of antioxidants on the thermooxidative stability of the polymers. Especially at elevated temperatures and in the presence of oxygen, polyolefines undergo thermooxidative degradation which follows a radical mechanism [98]. 

Lappin and Zannucci [5] showed that a number of ultraviolet light absorbers as well as antioxidants could be quantitatively determined on an SE-30 column. SE-30 has a maximum operating temperature of about 350 °C. This high temperature permits elution of some high molecular weight additives. 

Dobies [35] has described detailed procedures for determining various antioxidants in PE and PP films. A feature of this method is that it requires only a small polymer sample (5 g) for the determination of down to 0.02% antioxidant compared to sample sizes of up to 1 kg in previously reported procedures. They describe the extraction procedure used for isolating the antioxidants from the polyolefins, the TLC separation of various antioxidants used industrially, and a quantitative determination of the antioxidant to detect 0.02-0.20% of an antioxidant by the use of the double beam scanning densitometer. The six antioxidants he studied were 4,4 -butylidene (2-tert-butyl-5-methyl)phenol 4,4-thiobis(6-tcft-butyl-m-cresol) pentaerythritol tetrakis(3,5-di- er -butyl-4-hydroxyhydrocinnamate) 2,2 -methylenebis(4-methyl-6-tcft-butylphenol) octadecyl (3,5-di-tert-butyl-4-hydroxyphenyl) acetate and 2,6-di-tert-butyl-p-cresol. 

Strohecker [97] has worked out a procedure for quantitative determination of ascorbyl palmitate in oils and fats he oxidises with 2,6-dichlorophenol-indophenol and treats the reaction product with 2,4-dinitrophenylhydrazine. The 2,4-dinitroosazone of ascorbic acid is formed under these conditions and may be easily separated from other compounds containing phenolic groups such as tocopherols. He uses a silica gel H layer and chloroform-ethyl acetate (50 + 50) for TLC. After development, the brick red zone of the osazone is scraped off and determined colorimetrically in solution m sulphuric acid. Down to 0.001% of ascorbyl palmitate in antioxidant mixtures and in oils and fats can be determined with this procedure. 

Analytical techniques for the quantitative determination of antioxidants in plastics generally fall into two classes indirect (or destructive) and direct (or non-destructive). Indirect or destructive methods, as the name implies, require a significant alteration to the sample so that the antioxidant can be removed from the plastic material for subsequent detection. Direct or non-destructive methods, on the other hand, involve the direct examination of the plastic sample with minimal sample preparation. 

Although it would be interesting to study s-NMR for rubber vulcanisates, this nucleus has such low abundance and sensitivity that it is now not possible. On the other hand, P s-NMR is of more interest because of the sensitivity of the nucleus and lack of polymeric matrix interference the spectra can usually be acquired in a relatively short time. The main applications in polymer/additive deformulation are found in the analysis of phosphorous containing additives such as secondary antioxidants (e.g. Irgafos 168 and Sandostab P-EPQ), flame retardants and transesterification suppressants, as well as in quantitative determinations. P s-NMR is an efficient tool for the stmctural analysis of insoluble polyphosphates and melamine phosphates. 

Figure 2.27 shows the use of pyrolysis in the examination of very small samples (1 mg) of cured adhesives and the quantitative determination of the antioxidant 2,6-di-t rt-methylphenol (BHT). The py-... 

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