Thin-Layer Chromatographic Quantification of Three Alkaloid Compounds in Sophora alopecuroides and TLC—Bioautography for Screening Antioxidant Components

Summary This study aims at establishing a thin-layer chromatographic (TLC) scanning method for the determination of three alkaloids in Sophora alopecuroides and preliminary screening of antioxidant active components in S. alopecuroides with TLC—bioautography technology. The alkaloids in S. alopecuroides were identified by silica gel thin-layer chromatography; the expansion agent was toluene— acetone—methanol—ammonia—water (8:3:0.2:0.5:8), and the chromogenic agent was modified bismuth potassium iodide solution, sophoridine, matrine, and sophocarpine in S. alopecuroides by TLC scanning at 500 nm. The linear ranges were 0.4152–2.4912 μg for sophordine, 0.4245–2.5470 μg for matrine, and 0.4101– 2.4606 μg for sophocarpine, with correlation coefficients of 0.9939, 0.9956, and 0.9975. Ultraviolet (UV) method was used to determine the total scavenging activity of the 2,2-diphenyl-1-picrylhdrazyl (DPPH) free radical. The best TLC identification condition was selected, and the antioxidant activity of DPPH was screened with the color. DPPH tests indicated that IC 50 of S. alopecuroides was 0.40 mg mL −1 . The TLC—bioautography technology showed the alkaloids in the purple background, and a white spot was not evident. Precision, accuracy, and repeatability of the TLC scanning method were evaluated, and the results were in accordance with the requirements of methodology validation. S. alopecuroides exhibits certain antioxidant activity, but the three alkaloids do not exhibit an evident antioxidant effect, and the unknown components of S. alopecuroides show weak antioxidant effect. The specific components need further studies.