TLC-DENSITOMETRY DETERMINATION OF BITTER GLYCOSIDES IN THE CHINESE DRUG LONGDAN, RADIX GENTIANAE, AND ITS QUALITY EVALUATION

Longdan, radix Gentianae, is a well-known drug used in Chinese traditional medicine. The authors investigated the plant origin of this drug in Chinese market and found that nine species of the genus Gentiana are evolved (sec below). It is necessary to evaluate the drugs derived from these species. The contents of gentiopicroside, swertiamarin and sweroside are used as criteria of quality of the crude drug Longdan. The method of quantitative determination of the three bitter glueosides using TLC-densitometry was therefore investigated, especially the selection of solvent and method of extraction, and the stability of spots separated. A linear relationship between the amount of glucoside (less than 8μg) and absorbance was obtained for each bitter glucoside when using the following parameters: dual wavelength (sample wavelength: gentiopicroside 270 nm, swertiamarin 240 nm, sweroside 245 nm; reference wavelength: 400 nm), reflection mode, linear scanning, SX=3, slit width 10×0.5mm. Absolute methanol was found to be better than aqueous methanol or 95% ethanol for extracting gentiopicroside from the crude drug. The ultrasonic extraction method is superior than the cold or hot maceration method for its simplicity, rapidity and avoiding the interference of heat, especially for heat-sensitive components.The method is as follows: A suitable quantity of powdered crude drug is weighed and extracted with methanol in an ultrasonic apparatus for 40 minutes. The extract is directly spotted on a polyamide sheet alongside With the standard substances. Using EtOAc-MeOH-H₂O (20:2:1)as developing solvent, the sheet is developed twice in ascending mode; gentiopicroside, swertiamarin and sweroside in the extract were well separated. The spots were determined directly by a dual wavelength TLC-scanner, Shimadzu model CS-910, under the stated conditions. The average recovery of the above three bitter glucosides for three determinations were 99.23～100.20% with a variation of coefficient 0.8～1.7%. When the method was applied to the determination of secoiridoids present in commercial drugs for three determinations, the variation of coefficient were 0.8～4.2% for glucosides with a content over 1%, and 2.0～5.9% for glucosides with a content less than 0.6%. This method is sufficiently simple, rapid and accurate for routine analysis.The result of quantitative determinations of the three bitter glucosides in crude drugs derived from eight Gentiana species showed that the content of gentiopicroside and total bitter glucosides is higher (4.06～5.82% and 4.35～6.65%) in drugs derived from Gentiana rigescens, G. triflora, G. atuntsiensis, G. manshurica (Heilongjiang) and G. scabra (Liaoning) and lower (1.84～3.12% and 2.07～3.12%) in underground parts of Gentiana cephalantha and G. suffrutescens. Gentiopicroside contents in the aerial parts of the latter two species were so poor (1.06% and 0.2% respectively) that these aerial parts, especially that of Gentiana suffrutescens, are considered not suitable for use as the drug Longdan.