Determination of ascorbic acid by gas liquid chromatography
The product (orange powder, 50.0 g) was extracted with hot ethanol (6 x 50 ml) by percolation through a short chromatographic column fitted with a sintered glass filter. The extract was concentrated under reduced pressure at 40° C, transferred quantitatively to a volumetric flask, and diluted to 25 ml with ethanol. Samples of the extract (0.2 ml and 0.3 ml) were evaporated to dryness in a vacuum desiccator, and the residues were dissolved in a 0.02 M solution of triphenylethylene (TPE) in absolute pyridine (1 ml). Aliquots (0.1 ml) of these solutions were trimethylsilylated by addition of a mixture of hexamethyldisilazane (0.15 ml) and chlorotrimethylsilane (0.15 ml) in pyridine (0.7 ml), heating nearly to boiling, and setting aside for 15 min at room temperature. The reaction mixtures (0.4 μl) were injected directly into the gas chromatograph, the column temperature being maintained at 160° C until elution of the TPE ( 20 min after sample injection), after which the temperature was raised to 230° C until TMS sucrose was eluted and a stable base line was obtained. TMS ascorbic acid and the internal standard were well separated from the other extract constituents, the order of elution being citric acid, D fructose, α D glucose, ascorbic acid, β D glucose, TPE, and sucrose. By this procedure the product was found to contain 310.4 mg ascorbic acid/100 g, whereas the value obtained by titration with 2,6 dichlorophenolindophenol was 313.8 mg/100 mg.