Thiocyanate hydroperoxide

Another method is that based on the ferrous/ferric thiocyanate determination of hydroperoxides [1]. This exploits the ion-catalysed decomposition as shown by... 

Oxidative stress Lipid oxidation Oxygen absorption Manometric, polarographic Diene conjugation HPLC, spectrophotometry (234 nm) Lipid hydroperoxides HPLC, GC-MS, chemiluminescence, spectrophotometry Iodine liberation Titration Thiocyanate Spectrophotometry (500 nm) Hydrocarbons GC Cytotoxic aldehydes LPO-586, HPLC, GC, GC-MS Hexanal and related end products Sensory, physicochemical, Cu(II) induction method, GC TBARS Spectrophotometry (532-535 nm), HPLC Rancimat Conductivity F2-iP GC/MS, HPLC/MS, immunoassays... 

Phenan thro line (182) can be used instead of thiocyanate to form a complex with Fe(III) ions resulting from the oxidation of Fe(II), and the measurement is made at 500 to 510 nm. The use of 182 has the advantage of stability in the presence of air and also of allowing the use of hydrocarbon solvents for increased solubility of certain analytes. The method was applied for determination of hydroperoxides in natural rubber and synthetic elastomers, in the range of 10 to 20 ppm active oxygen. The sensitivity can be improved to less than 1 ppm, depending on the color of the sample solution. ... 

Chloroprene Peroxide. The efficiency of conversion of oxygen to total peroxides and hydroperoxide at various extents of oxidation was determined by iodometric methods. At up to 12% oxidation the proportion of hydroperoxide was constant at 20% of the whole. Ferrous thiocyanate likewise estimated a constant proportion (40%) of the total peroxide. Direct analysis of oxidates was somewhat difficult since the chloroprene tended to continue oxidizing during manipulation. Total peroxide estimates on chloroprene-free solutions of peroxide in toluene showed that at 20% oxidation 84% of the oxygen absorbed was present as peroxide groups. This is a minimum value since a small amount of the peroxide may have decomposed while chloroprene was being removed at —20°C. 

Several methods have been introduced which express the degree of oxidation deterioration in terms of hydroperoxides per unit weight of fat. The modified Stamm method (Hamm et at 1965), the most sensitive of the peroxide determinations, is based on the reaction of oxidized fat and 1,5-diphenyl-carbohydrazide to yield a red color. The Lea method (American Oil Chemists Society 1971) depends on the liberation of iodine from potassium iodide, wherein the amount of iodine liberated by the hydroperoxides is used as the measure of the extent of oxidative deterioration. The colorimetric ferric thiocyanate procedure adapted to dairy products by Loftus Hills and Thiel (1946), with modifications by various workers (Pont 1955 Stine et at 1954), involves conversion of the ferrous ion to the ferric state in the presence of ammonium thiocyanate, presumably by the hydroperoxides present, to yield the red pigment ferric thiocyanate. Newstead and Headifen (1981), who reexamined this method, recommend that the extraction of the fat from whole milk powder be carried out in complete darkness to avoid elevated peroxide values. Hamm and Hammond (1967) have shown that the results of these three methods can be interrelated by the use of the proper correction factors. However, those methods based on the direct or indirect determination of hydroperoxides which do not consider previous dismutations of these primary reaction products are not necessarily indicative of the extent of the reaction, nor do they correlate well with the degree of off-flavors in the product (Kliman et at. 1962). 

Michael BD, Adams GE, Hewitt HB, Jones WBG, Watts ME (1973) A posteffect of oxygen in irradiated bacteria A submillisecond fast mixing study. Radiat Res 54 239-251 Mihaljevic B, Katusin-Razem B, Razem D (1996) The reevaluation of the ferric thiocyanate assay for lipid hydroperoxides with special considerations of the mechanistic aspects of the response. Free Rad Biol Med 21 53-63... 

Lanthanum nitrate, analysis of anhydrous, 5 41 Lead (IV) acetate, 1 47 Lead(II) 0,0 -diethyl dithiophos-phate, 6 142 Lead (IV) oxide, 1 45 Lead(II) thiocyanate, 1 85 Lithium amide, 2 135 Lithium carbonate, formation of, from lithium hydroperoxide 1-hydrate, 5 3 purification of, 1 1 Lithium chloride, anhydrous, 6 154 Lithium hydroperoxide 1-hydrate, 5 1... 

Measurement of hydroperoxides is the classical method for quantifying lipid oxidation and a variety of assay procedures are available. The oxidation of ferrous to ferric iron by hydroperoxides in the presence of ammonium thiocyanate to produce ferric thiocyanate, which can be quantified spectrophotometrically at 505 nm, has been used extensively to study lipid oxidation in milk (Loftus-Hills and Thiel, 1946). Newstead and Head-ifen (1981) recommend that extraction of fat from whole milk powder be carried out in the dark when using this procedure to avoid artefactually high... 

B19. Bolscher, B. G., and Wever, R., A kinetic study of the reaction between human myeloperoxidase, hydroperoxides and cyanide. Inhibition by chloride and thiocyanate. Biochim. Biophys. Acta 788, 1-10(1984). 

Ferric Ion Complexes Other chemical methods based on the oxidation of ferrous ion (Fe ) to ferric ion (Fe ) in an acidic medium and the formation of iron complexes have also been widely accepted. These methods spectrophotometri-cally measure the abihty of lipid hydroperoxides to oxidize ferrous ions to ferric ions, which are complexed by either thiocyanate or xylenol orange (23, 28, 29). Ferric thiocyanate is a red-violet complex that shows strong absorption at 500-510 nm (8). The method of determining PV by coloremetric detection of ferric thiocyanate is simple, reproducible, and more sensitive than the standard iodometric assay, and has been used to measure hpid oxidation in milk products, fats, oils, and liposomes (8, 23). 

Peroxide value (P V) is the most commonly used measurement of lipid oxidation. The standard iodometric method requires a relatively large sample (5 g) when the lipid is only slightly oxidized. The ferric thiocyanate method, based on the oxidation of ferrous to ferric ion, involves colorimetric measurement of ferric thiocyanate. This method is more sensitive than the iodometric method and requires a relatively small sample (0.1 g). The PV is a useful measure for samples with low levels of oxidation and when the hydroperoxides are not decomposed. During prolonged oxidation, a maximum PV is reached and the value then begins to decrease due to peroxide degradation. This maximum value occurs early for soybean and rapeseed oil, due to the more rapid decomposition of the hydroperoxides of the polyunsaturated fatty acids. 

MERCURIC THIOCYANATE (592-85-8) Hg(SCN)i Moderately unstable solid. Possible violent reaction with strong oxidizers strong acids organic peroxides, peroxides and hydroperoxides potassium chlorate potassium iodate, silver nitrate, sodium chlorate, nitric acid. Incompatible with ammonia, chlorates, hydrozoic acid, methyl isocyanoacetate, nitrates, nitrites, perchlorates, sodium peroxyborate, trinitrobenzoic acid, urea nitrate. When heated, this material swells to many times its original bulk. Attacks aluminum in the presence of moisture. Decomposes above 329°F/165°C, releasing toxic mercury and cyanide fumes, and sulfur and nitrogen oxides. On small fires, use dry chemical powder (such as Purple-K-Powder), alcohol-resistant foam, or COj extinguishers. MERCURIC (Spanish) (7439-97-6) see mercury. 

Conjugated diene formation can be measured by following the changes in absorbance at 234 nm [87], the wavelength maximum at which these dienes absorb. Hydroperoxide formation can be directly determined by HPLC [88 89] or indirectly by the thiocyanate method, in which hydroperoxides react with FeCl2 and thiocyanate to give a red colour which can be measured at 500 nm [90]. 

Determination of Lipid Hydroperoxides with the Ferric Thiocyanate... 

Aluminum acetate Aluminum caprylate Aluminum distearate Aluminum myristates/palmitates Aluminum stearate Aluminum tristearate N-2-Aminoethyl-3-aminopropyl trimethoxysilane Aminoethylethanolamine Aminomethyl propanol Aminopropyltriethoxysilane Aminopropyltrimethoxysilane Ammonium benzoate Ammonium borate Ammonium citrate dibasic Ammonium laureth sulfate Ammonium laureth-5 sulfate Ammonium laureth-7 sulfate Ammonium laureth-12 sulfate Ammonium laureth-30 sulfate Ammonium lauryl sulfate Ammonium maleic anhydride/diisobutylene copolymer Ammonium oleate Ammonium persulfate Ammonium polyacrylate Ammonium potassium hydrogen phosphate Ammonium stearate Ammonium sulfamate Ammonium thiocyanate Ammonium thiosulfate Amyl acetate Antimony trioxide Asbestos Asphalt Azelaic acid 2,2 -Azobisisobutyronitrile Barium acetate Barium peroxide Barium sulfatej Bentonite Benzalkonium chloride Benzene Benzethonium chloride Benzothiazyl disulfide Benzoyl peroxide Benzyl alcohol Benzyl benzoate 1,3-Bis (2-benzothiazolylmercaptomethyl) urea 1,2-Bis (3,5-di-t-butyl-4-hydroxyhydrocinnamoyl) hydrazine 4,4 -Bis (a,a-dimethylbenzyl) diphenylamine Bisphenol A Bis (trichloromethyl) sulfone Boric acid 2-Bromo-2-nitropropane-1,3-diol 1,4-Butanediol Butoxydiglycol Butoxyethanol Butoxyethanol acetate n-Butyl acetate Butyl acetyl ricinoleate Butyl alcohol Butyl benzoate Butyl benzyl phthalate Butyidecyl phthalate Butylene glycol t-Butyl hydroperoxide... 

It should be noted that a hydroperoxide molecule consumes 2Fe. The titration is done after complexation of the ferric iron (Fe ) by ammonium thiocyanate, leading to a red complex readily titrated by colorimetry at 512 nm. 

The results obtained by CL quantification of lipid hydroperoxides in different types of oils were compared with those obtained for PV with the IT method and the iron thiocyanate method. By using the emulsion FI-CL procedure, a nonlinear response between CL signal and the concentration of oils from analyzed samples was obtained. This was explained by differences in turbidity between samples (due to the different amount of oils contained in the analyzed sample). When samples that contained the same quantity of oil but increased concentration of LOOH were used, the relationship between LOOH concentration and CL intensity was linear (r = 0.9908). 

The iodometric method can be used only when the hydroperoxides are thermally stable, up to 80°C. On the other hand, the thiocyanate method is... 

Hydroperoxide (OOH) groups can be determined colorimetrically with thiocyanate [NH SCN—FeS04(NH4)2S04 6H20] reagent [26,1406,1713, 1714, 1996, 2327] ... 

The application of colorimetric methods for the analysis of hydroperoxides in polymers requires the sample to be dissolved, or at least swollen, in a solvent (the reactants have to diffuse into the amorphous regions in the polymer matrix). The polymer sample should be in contact with the reagent for a minimum of 30 min (in the dark). A mixture of benzene-methane (95 4 or 92 8) can be used as a solvent for polyolefins or poly(vinyl chloride). The colorimetric measurements are carried out at A = 512.5 nm (A, of the ferric thiocyanate complex). The concentration of hydroperoxide in the polymer sample is calculated according to the expression ... 

A = absorbance of a sample in a 1 cm cell, as measured against the blank solution (thiocyanate reagent in pure benzene) e = stoichiometric coefficient of hydroperoxide interaction with the reagent... 

It has been reported that the thiocyanate method gives values of hydroperoxide content in oxidized polyolefins one order of magnitude below the true level because of the failure of the reagents to penetrate into the oxidized polymer films even after a prior swelling step. 

The hydroperoxides in peroxidation system before and after heating for 60 min were measured according to the method described by Mituda 14), That is, 100 il of reaction mixture were mixed with 4.5 ml of 75% ethanol, 100 pi of 30% ammonium thiocyanate, 200 pi of 0.1 N HCl, and 100 pi of 20mM ferrous chloride in 3.5% HCl. The production of hydroperoxides in this mixture was measured at 500nm. 

Lipid oxidation was monitored through analysis of the hydroperoxide content measured via the ferric thiocyanate method [64]. Oil was extracted from an aqueous emulsion prepared from the microcapsules using isooctane/2-propanol 50 50 (v/v). Headspace gas chromatographic analysis of secondary lipid oxidation products was performed in the majority of trials, but since correlation of propanal as a key compound was always very good with the hydroperoxide content, data are not reported in this chapter. 

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