Study On Supercritical CO₂ Fluid Extraction Of Heavy Metals From Dioscorea Zingiberensis C.H. Wright

Dioscorea Zingiberensis C. H. Wright is an important unique economic plant, whoseactive ingredient is called sapogenins and used in the synthesis of the body hormonemedicine as the foundation raw material, which makes it called officinal gold. In order toreduce the content of heavy metals in Dioscorea Zingiberensis C. H. Wright, and protectthe active ingredient, the technology of extracting Cu, Cd, Pb by supercritical CO₂ fluid,and the influence of depuration of heavy metals on the active ingredient were investigated.The main contents and results are listed as follows:1. Determination of Cu, Cd, Pb in Dioscorea Zingiberensis C. H. Wright(1) The microwave digestion method was investigated and compared with theorganic solvent extraction method. Experimental results showed that, the former methodhad the advantages of faster speed, less usage amount of digestive dissolvent and higheraccuracy.(2) Microwave digestion-flame/graphite furnace atomic absorption spectrometrymethods were established for the determination of Cu, Cd, Pb in Dioscorea ZingiberensisC. H. Wright. The content of Cu, Cd, Pb was 3.60μg/g, 0.28μg/g and 11.51μg/grespectively under optimum conditions.2. Supercritical CO₂ fluid chelating extraction of Cu, Cd, Pb from DioscoreaZingiberensis C. H. Wright(1) The effects of chelating agent, chelating mode, extraction pressure, temperature,time and content of modifier on extraction yield were investigated. Experimental resultsshowed that, sodium diethyldithiocarbamate was the best used as the chelating agent forthe extraction of heavy metals. It must be mixed into the sample before extraction for 1h.Extraction pressure, temperature, time and content of modifier all had positivecorrelation with extraction yield in intial stage.(2) Four-factor and three-level orthogonal design was used to optimize the extractionconditions. The influence of various factors was in the order: pressure＞temperature＞time＞content of modifier.(3) Based on orthogonal test, three levels of the factors were selected to the centralcomposite design experiment. The quadric regression model for the purifying rate wasestablished. The model was significantly fit well and the optimum combination wasobtained by response surface analysis and ridge analysis. Results showed that, pressure, temperature and time were all significant to the purifying rate. When the extractionparameters were composed of 25.54MPa, 59℃and 35min, the purifying rate reachedmaximum, which was verified to 75.10% and predicted to 71.71%. After depuration, thecontent of heavy metals in Dioscorea Zingiberensis C. H. Wright reached the limitedquantity of international standard.3. Influence of depuration of heavy metals in Dioscorea Zingiberensis C. H.Wright on the active ingredient(1) Supercritical CO₂ fluid chelating extraction was investigated and compared withthe organic solvent extraction method. Experimental results showed that, the formermethod had the advantages of high recoveries, safety, efficiency, simple crafts, lowoperating temperature and clean.(2) The ultraviolet spectrophotometry method as determining the content ofsapogenins was used to evaluate the change of the quality in Dioscorea Zingiberensis C.H. Wright before or after supercritical CO₂ fluid extraction. The content of sapogeninswas 2.03% and 1.84% respectively in original and depurative sample, which showed thatdepuration of Cu, Cd, Pb in Dioscorea Zingiberensis C. H. Wright by supercritical CO₂fluid extraction had little influence on the active ingredient.