COMPARISON OF METHODS FOR THE EXTRACTION OF FLAVONOIDS FROM BIRCH LEAVES (BETULA-PENDULA-ROTH) CARRIED OUT USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The efficiency of commonly used methods and solvents for the extractio n of flavonoids from dried birch leaves was compared, and the response s of individual compounds were determined. The three methods compared were (1) a short extraction with a clipping homogenizer in an unheated solvent, (2) refluxing, and (3) Soxhlet extraction. The solvents test ed (pure and 80 % aqueous solvent) were acetone, ethanol, and methanol . In general, the aqueous solvents were superior to the nonaqueous sol vents. Methanol was the most efficient nonaqueous solvent, and in refl uxing and Soxhlet extraction, the yield of flavonoid glycosides was co mparable to that in aqueous methanol. Soxhlet extraction and refluxing were found to be efficient methods with several solvents. Refluxing w as more efficient than homogenizing, but neither method revealed any s ignificant differences among the aqueous solvents. The responses of in dividual compounds were fairly similar, except in procedures resulting in the lowest yields. Refluxing in nonaqueous methanol is recommended as the most convenient exhaustive extraction method for flavonoid gly cosides. If the use of a heated solvent is undesirable, homogenizing i n aqueous ethanol is recommended as the best compromise between safety and efficiency.