A colorimetric method for the determination of glycerides

Abstract

A colorimetric method for the determination of glycerides (Short communication) J.-TH. MORSEL and R. HEYERThe quantitative determination of lipids is, a universal and repeating problem of analytical chemistry in different fields, for example food-or biochemistry. Important criterions to value methods are the time needed for analysis, reproducibility and detection limit. The determination of glycerides can be performed by classical methods, for instance by the WEIBULL-STOLDT method [I] or by extraction. HPLC and GLC can be used successfully, too. All these methods are expensive of time or equipment.In this paper a colorimetric method is reported characterized by good reproducibility, great sensitivity and little time needed to perform. The determination, first time reported by FLETCHER [2] is based on the oxidation of glycerol after saponification of the lipid with periodate. The formaldehyde produced is determined by coupling a dye in a HANTZSCH condensation with ammonium ions and 2,4-pentadione. The 3,5-diacetyl-1,Cdihydrolutidin formed is measured in a photometer at 410nm. MaterialsPotassium hydroxide solution. 5 % in isopropanol/water, 4: 6 (v/v).Sodiummetaperiodate stock solution. 0.025 M in 1 N acetic acid. The working solution is prepared by mixing 12 ml stock solution, 20 ml isopropanol and 68 ml 1 N acetic acid. Acetylacetone solution. 0.75 ml 2,4-pentadion and 2.5 ml isopropanol are completed with 2 M ammonium acetate buffer (pH 6) to 100 ml. The pH should be determined exactly. The solution can be stored in dark bottles in a refrigerator.Water used for preparing the solution should be bidistilled. Isopropanol has to be free of n-alcohols. It has to be distilled before use.Standard solutions of glycerol (0.3 mg/100 ml), triolein (14 mg/100 ml) and tricaproin (3.5 mg/100 ml) are prepared by dissolving the substances in isopropanol/water 9: 1 (v/v). The triglycerides must be free of glycerol. This will be reached by filtration of crude products over a silica column. MethodsThe determination was performed by the FLETCH~X method [2] with some modifications. 2 ml of sample are shaken with 0.6 ml potassium hydroxide solution in a stoppered test tube and heated for I5 min to 60-70 "C. After cooling in a water bath to room temperature 1 ml of fresh prepared periodate solution is added and after shaking vigorously 0.5 ml acetylacetone solution is added and colour is developed at 50 "C within 30min. The colour is measured in a photometer at 410nm against isopropanol/water 9 : 1 (v/v). The extinction of a blank test (2 ml isopropanol/water and all reagents) is substracted. ResultsThe method has been tested with glycerol, triolein and tricaproin. Calibration curves are linear in a wide range (Fig. 1). In the experiments the minimum detectable concentration of glycerol was 70 pg/lOO ml. This indica-

Acetalization of glycerine at presence of acid-modified clinoptilolite, bentonite and tripolite from the domestic deposits

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Food Packaging and Preservation

“…It is in the initial phase that this photooxidation differs from autooxidation, in which the oxygen reacts with the double bonds in the absence of photons. 132 …”