Comparison between sequential and single extraction procedures for metal speciation in fresh and dried Sedum Plumbizincicola

Abstract

Sequential and single extraction procedures were applied to both fresh and dried Sedum Plumbizincicola leaves and stems. The extractants, different from those of soil, sediment or sewage sludge metal fractions, were water, 80% (v/v) ethanol, 1 mol/L NaCl, 2% HAc and 0.6 mol/L HCl. Zn, Cd and Cu in the extracts and samples were measured by flame atomic adsorption spectrometry. In sequential extraction procedures, water soluble form and ethanol soluble form are the main fractions for Zn, while water soluble form and NaCl soluble form for Cd, and comparatively uniform distribution for Cu with the residue form most and HCl soluble form second. Single extraction procedures are used to compare the extraction efficiencies of the five reagents to screen appropriate extractants and operating conditions for liquid extraction to deal with large amount of harvested metal-contained biomass, which will pose a threat to the environment if treated improperly. The sequences of extraction efficiencies are HCl>NaCl≈HAc>Water≈Ethanol for Zn and HCl≈NaCl≈HAc>Water>Ethanol for Cd. As for Cu, all the five extractants cannot effectively extract Cu, but HCl achieves a higher efficiency (>70% in fresh samples, and 45%–60% in dried samples). Besides, extraction efficiencies for most extractants in fresh samples are higher than those in dried samples, and extraction efficiencies of stems and leaves for the five extractants are close. The two extraction procedures can obtain high degree of accuracy with the relative standard deviation (RSD) lower than 10%, and metal recoveries are controlled between 80%–120% with most of 90%–110%.