Saponification methods

Ester groups occur in a wide range of polymers, e.g., polyethylene terephthlate. The classic 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 be determined by GC. The alcohols formed by the hydrolysis of the acrylate esters are determined by GC. Polymethyl acrylate can be hydrolysed rapidly and completely under alkaline conditions however, the monomer units in polymethylmethacrylate (PMMA) 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. 

Anderson and co-workers [5] used combined Zeisei reaction and GC to analyse acrylic copolymers. Acrylic esters were cleaved with hydriodic acid and gas chromatography was used for analysing the alkyl iodides so formed  

Using this procedure, the recovery of alkyl iodides is greater than 95% for polymers containing between 10 and 90% of the methyl, ethyl, and butyl esters of acrylic and methacrylic acid. In addition, the use of isopropylbenzene as the trapping solvent allows the determination of all Cj to C4 alkyl iodides. 

Polymer Methyl acrylate % Methyl methacrylate % Ethyl acrylate % Ethyl methacrylate % Butyl acrylate % Butyl methacrylate % 

The Ziesel reaction has been used for the determination of alkoxyl groups in cellulosic materials [6-8] and the determination of ether groups in cellulose and polyvinyl ethers [9]. However, hydriodic acid also cleaves any ester linkages on the polymer backbone, giving positive interference. 

A copolymer of ethylene and vinyl acetate has the following structure which, upon hydrolysis in the presence of excess standard potassium hydroxide/p-toluene sulfonic acid catalyst reacts as follows  

Excess potassium hydroxide is then determined by titration with standard acetic acid, and hence the vinyl acetate content of the polymer is calculated from the amount of potassium hydroxide consumed. Vinyl acetate ethylene copolymers can be determined by saponification with 1 N ethanolic potassium hydroxide at 80 °C for 3 hours [53, 54]. 

Saponification methods have been applied to the determination of ester groups in alkyd resins [55-57], polyesters, cellulose, polyvinyl esters, polyacrylates and polymethacrylates [58-60]. 

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In this group we place mainly the neutral bacterial slimes and reserve carbohydrates. They are better defined products than those previously dealt with and as such may of course be regarded as true polysaccharides. Invariably, however, saponification methods are required to rid them of protein residues and to make them water-soluble. The more soluble mold polysaccharides appear to lose their protein constituents by autolytic processes during the longer periods required for mold metabolism. Mold slime production can, however, readily be demonstrated on a solid medium. It is proposed here to give briefly some of the types of structure known in the group. 

Normally, odd-numbered fatty acids are used as internal standards. While the use of internal standards ensures the correctness of the extraction procedure, it does not guarantee the completeness of extraction for different fatty acids. Due to this reason, a comparison between the methods is essential to truly determine the efficacy of extraction. Chavarri et al. (1997) compared two sample preparation procedures. The first method was the direct method developed by de Jong and Badings (1990), described above. The second method involved saponification with TMAH as described by Martin-Hemandez et al. (1988) and the formation of methyl esters in the injector prior to analysis. The authors found that separation of the FFAs from the triglycerides prior to derivatization improved the analysis. Another comparative study by Ardo and Polychroniadou (1999) reported that the saponification method described above (Martin-Hernandez et al., 1988) was found suitable for both low and high FFA levels in cheese. 

Larsen, E. Christensen, L.P. 2005. Simple saponification method for the quantitative determination of carotenoids in green vegetables. J. Agric. Food Chem. 53 6598-6602. 

In the second step, the two methyl ester moieties are hydrolyzed under basic conditions to the corresponding carboxylic acids. Whereas typical saponification methods (2 N KOH, reflux, 48 h) failed, the hydrolysis proceeded smoothly with "anhydrous hydroxide".This reagent - relatively unsolvated hydroxide - was generated via the reaction of two equivalents of potassium /er/-butoxide with one equivalent of water. 

The next step was the saponification method in which an outer layer of the fibre was hydrolysed to cellulose with sodium hydroxide, creating an affinity for direct dyes. The process was soon abandoned because the results were uncertain and the effect on the properties of the rayon was not good. 

In Experiment 4 the same sediment sample was extracted by Methods III and V successively. This experiment (Table V) showed that the saponification (Method V) returned additional material from the sediment however, most of this material was unresolved and in the F-l fraction. The amount of additional F-2 material returned by the second extraction was only about 11%. This experiment showed that a method may be suitable for one class of petroleum hydrocarbons but not be as effective for recovering other classes. 

Methoxyl Content. The saponification method of von Fellenberg (, ff) was used to determine the methoxyl content, and the results in Table I are expressed on the basis of 100% calcium pectate for uniformity. The methoxyl content of the calcium pectinates prepared by acid de-esterification ranged from 3.1 to 6.4% Trend curves, showing a comparison of de-esterification as denoted by the methoxyl contents of the alcohol-recovered samples and calcium-precipitated samples, are presented in Figure 2. Under comparable conditions of pH and time of treatment, the methoxyl contents of the alcohol- and the calcium-precipitated samples prepared by acid de-esterification at 60 C. were similar. 

Ester or amide groups Saponification method Alfrey, 1964... 

The total lipids are first extracted from food with ispropanol/petroleum ether (3 1 v/v) or with acetone. Alkaline hydrolysis follows, removing the extracted acyl-hpids and the carotenoids from the unsaponifiable fraction. This is the usual procedure when alkali-stable carotenoids are analyzed. Although carotenoids are generally alkah stable, there are exceptions. When alkah-labile carotenoids are present, the acyl lipids are removed instead by a saponification method using column chromatography as the separation technique. 

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