Saponification procedures

Ester groups occur in a wide range of polymers. The classical chemical method for the determination of ester groups, namely saponification, can be applied to some types of polymer. For example, copolymers of vinyl esters and esters of vinyl esters and esters of acrylic acid can be saponified in a sealed tube with 2 M sodium hydroxide. The free acids from the vinyl esters can then he determined by GC. Polymethyl acrylate can be hydrolysed rapidly and completely under alkaline conditions however, the monomer units in polymethylmethacrylate prepared and treated similarly are resistant to hydrolysis although their benzoate end-groups react readily. Thus, saponification techniques should be applied with caution to polymeric materials. 

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Acidity is determined by glc or titration, and the dimer content of acryhc acid by glc or a saponification procedure. The total acidity is corrected for the dimer acid content to give the value for acryhc acid. 

We always recommend that structural changes occurring after the saponification procedure be verified. Since the hydroxyl groups have no influence on the chromophore, the wavelength of the maximum absorption, shape, and intensity of the ultraviolet-visible (UV-Vis) spectrum would be identical for unsaponified and saponified samples. 

In solution, vitamin D (both D2 and D3) isomerizes to previtamin D and forms a temperature-dependent equilibrium mixture [520], which leads to quantification problems. Previtamin D is difficult to quantify because of interference from co-eluted contaminants. The reversibility of the isomerization is very slow, therefore the percentage of previtamin can be considered constant during the entire analysis. The quantification of the potential vitamin D can be performed using an external standard that has undergone saponification procedure as the sample [521]. Vitamin D2 and D3 can be used as an internal standard to quantify the other one. Indeed, the isomerization rates of vitamins D2 and D3 are virtually the same thereby the previtamin D/vitamin D ratio will be the same for both vitamers at any temperature. The isomerization problem can be resolved by... 

Saponification causes a significant loss of xanthophylls, even when carried out under relatively mild conditions (ambient temperature for 3 h) (21). In addition, several different saponification procedures have been shown to promote the formation of cis isomers of /3-carotene (74). Since saponification prolongs the analysis and is error prone, it should be carried out only when needed, as in high-fat samples or those containing carotenol esters. 

HE Indyk. Simplified saponification procedure for the routine determination of total vitamin E in dairy products, foods and tissues by high-performance liquid chromatography. Analyst 113 1217-1221, 1988. 

In using this saponification procedure a salting-out of dioxane often was observed. Since such a salting-out effect can be quite troublesome, it became necessary to initiate a study of the three-compound system in order to learn how such a complication might be avoided. 

Extraction of Active Compounds from Food. Vitamins are the group of compounds more usually extracted from foods using SFE (83). A method for the analysis of the natural contents of vitamins A and E in milk powder based on SFE, a miniaturized alkaline saponification procedure, and HPLC was proposed by Turner and Mathiasson (84). Modifications of the sample matrix, the combination of static and dynamic extraction modes, and the effect of changes in extraction parameters such as temperature, flow rate, time, collection solvent, and collection temperature were optimized, obtaining recoveries of 99% and 96% for vitamins A and E, respectively. Another method for the determination of vitamins A and E based on the coupling of SFE-enzymic hydrolysis-HPLC has also been proposed providing recoveries between 79% and 152% (85). 

This section begins with the extraction of a dehydrated sample. It continues with a saponification procedure to initiate the isolation of the carotenoid mixture. During saponification, the esters are hydrolyzed and the free pigments released. Then, to continue the isolation, open-column chromatography (OCC) is suggested as a simple and fast means of separating the three main groups of carotenoids based on their different polarities. 

The xanthophylls and carotenes of plants are examined conveniently after removal of the chlorophylls by saponification with alkali. For this saponification, add 10 ml of 30% potassium hydroxide in methanol to the centrifuged acetone or methanol extract in the separatory funnel. After 30 min with occasional swirling, add 40 ml of cold petroleum ether (20-40°C)-diethyl ether (1 1) plus 100 ml of 10% aqueous sodium chloride solution. Wash the resultant upper golden-yellow layer with water and take to dryness as above. Prepare the sample solution by dissolving the residue in 1 ml of petroleum ether (60-110°C)-diethyl ether (1 1). This saponification procedure should not be employed with plant extracts containing xanthophylls that are decomposed by alkalies, as are fucoxanthin from diatoms and brown algae and peridinin from dinoflagellates. 

Saponification procedures can be applied to the determination of ester groups in polymers. A copolymer of ethylene and vinyl acetate has the following structure which, upon hydrolysis in the presence of potassium hydroxide/p-toluene sulfonic acid catalyst [32, 33] reacts as follows ... 

To simplify carotenoids analysis, saponification procedures are employed before LC to release all the carotenoid esters as their respective free forms. However, it has been demonstrated that this saponification may change the native carotenoid composition, producing a loss of... 

Ziesel reduction followed by gas chromatography or pyrolysis followed by gas chromatography have the advantage of being more specific for the determination of ester groups than standard saponification procedures. 

Our continued search for better alternatives to traditional saponification procedures led to the use of tetraalkylammonium hydroxides. Tetraalkylammonium hydroxides are very strong bases and have the advantage of being soluble in water and in many organic solvents. However, these bases, except for some scattered reports, were not fully utilized in carboxylic ester hydrolysis, particularly for polypeptide esters. The use of tetraalkylammonixim hydroxides in hydrolysis of small easily soluble polypeptide esters does not show much of an advantage over the traditional conditions such as NaOH in aqueous acetone. However, fully-protected larger polypeptide chains, which show... 

From the unsaponifiable matter of Spheciospongia vesparia, Bergmann and McAleer (22) isolated a crystalline fraction which was shown to be metanethole (225), the dimerization product of anethole. From the lack of optical activity the authors suspected that this sponge product was an artifact formed during the saponification procedure. 

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