Rose-Gottlieb method

The fat-soluble vitamins can be extracted from the food matrix without chemical change using a solvent system that is capable of effectively penetrating the tissues and breaking lipoprotein bonds. A total lipid extraction is required for the simultaneous determination of vitamers or vitamins with a wide range of polarities, and, for this purpose, a mixture of chloroform and methanol (2 + 1) is highly efficient (82). The Rose-Gottlieb method is particularly suitable for ex-... 

For the determination of vitamin E in seed oils by HPLC, the oils can simply be dissolved in hexane and analyzed directly. Solid-food samples demand a more rigorous method of solvent extraction. In a modified Rose-Gottlieb method to extract vitamin E from infant formulas (86), dipotassium oxalate solution (35% w/v) was substituted for ammonia to avoid alkalizing the medium, and methyl tert-butyl ether was substituted for diethyl ether because of its stability against the formation of peroxides. 

The methods available were critically examined by Garratt with a view to accurate determination both of the oil and the vitamin A content. The Rose-Gottlieb and Gunn and Venables methods were considered most suitable to satisfy both requirements provided the oil present has not hydrolysed. The Rose-Gottlieb method is as follows ... 

Extract of malt with cod-liver oil has been found to develop excessive acidity, probably by the action of lipase present in the malt extract. This acidity may be so great as to give discordant results with the Rose-Gottlieb method, the discrepancy being due to the formation of ammonium soaps, some proportion of which is extracted by the mixed ethers as acid soaps, the amount varying with the conditions. It has also been shown that low results are obtained with the Gunn and Venables method for such acid... 

The total fatty matter may be determined by a modified Rose-Gottlieb method proposed by Bond and Druce. The essential details are as follows ... 

A high level of FFAs may cause minor errors in determination of the fat content of milk (e.g., a decrease of 0.01 0.03% fat per 1 meq/100 g increase in FFA), whether by older methods such as Rose-Gottlieb or turbidimetric or infrared methods (van Reusel, 1975 van de Voort et al., 1987). Lipolysis may also lead to false positives in testing for antibiotic residues in milk (Carlsson and Bjorck, 1992). 

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