A method for determining the carbonyl value in thermally oxidized fats

Abstract

A simple method for the determination of the earbonyl value of thermally oxidized fats, using hydroxylamine hydrochloride, is described. Normal octyl alcohol containing pyridine was used as a solvent, and the reaction was allowed to proceed at room temperature for 24 hrs. The titrations were carried out with the aid of a pH meter. The method was standardized against aliphatic aldehydes and ketones. The restflts of analyses showed that the different pure compounds reacted to an extent of 98% or better at room temperature.The method has been successfully applied for the deterruination of the earbonyl value of themnally oxidized fats. n-Valeric acid and the fatty acids with higher molecular weight were not found to interfere in the determination of the carbonyl value by the present method.NUIVIBER of analytical procedures for the determination of aldehydes and ketones, based on the use of hydroxylamine hydrochloride, have been reported. The amount of earbonyl oxygen present was quantitatively determined by estimating either the amount of unreaeted hydroxylaminc (1,2) or the amount of water formed during the reaction (3), or by estimating the hydrochloric acid liberated (4,5,6, 7,8). Lappin and Clark (9) have described a procedure which employs 2,4-dinitrophenylhydrazine for determining traces of carbonyls in aqueous or alcoholic solutions. This method with some modifications was employed by Heniek et al. (10) for the determination of carbonyls in rancid fats and foods. These analytical procedures were not found to be reliable for the quantitative determination of carbonyl oxygen in thernmtly oxidized fats because of their limited solubility in all but a few suitable solvents. A method for the determination of the carbonyl content of thermally oxidized fats, using hydroxylamine hydrochloride as a reagent and n-oetyl alcohol as a suitable solvent, is presented in this paper. Experimental ReagentsHydroxylamine Hydrochloride Reagent. Thirtyfive grams of hydroxylamine hydrochloride (reagent grade) were dissolved in 160 ml. of distilled water, and the resulting solution was diluted to 1 liter with 95% earbonyl-free ethyl alcohol.Standard Sodium Hydroxide in Methanol. Twenty grams of sodium hydroxide (analytical reagent) were dissolved in a small amount of water and diluted to 1 liter with absolute methyl alcohol and standardized against standard hydrochloric acid (0.5 N).Pyridinc-octyl Alcohol Solvent. Five ml. of pyridine (analytical reagent) were diluted to 1 liter wth n-octyl alcohol.A Beeknlan ptI meter, Laboratory Model H2, equipped with standard glass electrode and standard calomel electrode, wtcs used in this work. Analytical ProcedureOne gram of the sample to be analyzed was weighed into a 250-ml. glass-stoppered Erlenmeyer flask. Fifty ml. of pyridine-oetyl alcohol solvent were pipetted into it, and, if necessary, the flask was heated on a hot plate until the sample was dissolved. Fifteen ml. of hydroxylamine hydrochloride reagent was then added with a pipette. The flask was stoppered, the contents were mixed we...

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