Removal of trace heavy metals from a natural medicine material by supercritical CO2 chelating extraction

Removal of arsenic, mercury, lead, and copper from a natural medicine mater ial by supercritical carbon dioxide containing a chelating ligand, diethyla mmonium diethyldithiocarbamate (Et2NH2DDC), was studied. The contents of As , Hg, Pb, and Cu in the natural medicine material, which was a mixed powder of six plants, were <2, 0.2, 2, and 10,mug/g, respectively. It was shown t hat Et2NH2DDC was an effective ligand for the extraction of the heavy metal s. The effects of pressure, temperature, modifier, and time on the extracti on were systematically investigated. The results showed that there were the extraction efficiency-based optimal temperatures of arsenic, lead, and cop per with the order T-m,(Pb) < T-m,(As) < T-m,(Cu), while the extraction eff iciency of mercury decreased as the temperature increased. When the pressur e or the amount of the modifier, ethanol in supercritical CO2, was increase d, the extraction efficiencies of arsenic, lead, and mercury were not enhan ced noticeably, while the extraction efficiency of copper increased markedl y. Except for lead, the extraction efficiencies of As, Hg, and Cu increased as the extraction time extended. With the suitable pretreatment, the natur al medicine material in which the content of arsenic was 4 times more than the limit of the U.S. Food and Drug Administration (FDA) could meet the sta ndard after the extraction with Et2NH2DDC in supercritical ethanol-modified carbon dioxide.