EFFECT OF SAMPLE PREPARATION METHOD ON BIRCH (BETALA-PENDULA ROTH) LEAF PHENOLICS

Sample preparation methods for high-performance liquid chromatographic analysis of birch leaf phenolics were compared. The methods tested we re: (1) air-drying at ambient temperature, (2) oven-drying at 40 degre es C, (3) oven-drying at 80 degrees C, (4) freeze-drying, prefreezing with liquid N-2, (5) freeze-drying, prefreezing at -18 degrees C, (6) freeze-drying without prefreezing, (7) storing frozen for 12 days with out drying, and (8) immediate extraction of fresh samples. Although th ere were significant differences among methods in absolute concentrati ons of phenolics, none of the methods altered considerably the phenoli c profile of birch leaves. For quantitative analysis, the samples shou ld be analyzed immediately. Alternatively, the samples may be stored f resh frozen, at least for a short time. Among the drying methods, the highest concentrations of phenolics were obtained by freeze-drying of slowly frozen leaves (method 5). Freeze-drying without prefreezing res ulted in significantly lower concentrations of flavonoid glycosides th an method 5. Oven-drying did not prove to be a good alternative to con ventional freeze-drying, nor did it show any advantage over simple air -drying.