Research On The Determination Of Heavy Metals In Medicinal Herb Samples

Medicinal herb samples are not only the treasure of the Chinese nation, but also the carrier of the inheritance of Chinese national culture. They have lots of advantages, such as mild side effects, easy to identification, pharmacology, effective and lasting. Therefore, they are welcomed at home and abroad. The toxicity and effect of trace heavy metals on human health and the environment has attracted considerable attention and concern in recent years. Heavy metals were dangerous in the form of cations and bonded to short chains of carbon atoms. Potential toxicity of heavy metals resulted from the fact that they could produce stable hydrophobic chelates with a range of both organic and inorganic ligands. And they could harm the natural environment at low concentrations, with an inherent toxicity. What’s more, they also had a tendency to accumulate in the food chain. Contamination in medicinal herb samples with heavy metals may be due to irrigation with contaminated water, metal-based pesticides and fertilizers, industrial, transportation, harvesting process and storage. Therefore, it was quite essential to build some accurate and convenient methods for the determination of heavy metals in medicinal herb samples. In this paper, we have studied several methods to explore the determination of some heavy metals in medicinal herb samples. And the main research contents were as follows: Part1Determination of heavy metals in medicinal herb samples by HPLC with ultrasound assisted cloud point extraction (UA-CPE)The UA-CPE method was developed to detect manganese, chromium and nickel in medicinal herb samples, combined with HPLC. Ammonium pyrrolidinedithiocarbamate (APDC) was adopted as complexing agent and2.0%(v/v) Tergitol TMN-6as the extractant. The optimized experimental conditions were ultrasonication at35kHz and45℃for30min. Then, the solution was centrifuged for5.0min at3000rpm. The calibration plots were found to be linear in the range of0.02-0.5mg/L for Mn and Cr, meanwhile0.05-1.0mg/L Ni, and the linear correlation coefficients were between0.9959and0.9999, the recoveries ranged from91.8%to97.8%and the relative standard deviations (RSD) were between1.8%and5.5%(n=3). The limits of detection (LOD) were0.16μg/L for Mn,0.56μg/L for Cr and5.1μg/L for Ni, respectively. The method shortened the extraction time and improved the extraction efficiency and stability. And the proposed approach was applied to determine Mn, Ni and Cr in medicinal herb samples with satisfactory results. Part2Determination of heavy metals in medicinal herb samples by flame atomic absorption spectrometry (FAAS) with supramolecular solvent-based microextraction (SUSME)The method was based on Cu and Co reacted with1-(2-Pyridylazo)-2-naphthol (PAN) to yield hydrophobic chelates (M-PAN), which were preconcentrated in supramolecular solvent (SUPRAS) phase made up of octanoic acid and tetrahydrofuran (THF) and determined by flame atomic absorption spectrometry (FAAS) without the interference from other heavy metals. Under optimized experimental conditions, calibration plots were found to be linear in the range of0.1-5.0mg/L for Cu and Co, the linear correlation coefficients were0.9967and0.9969, the recoveries ranged from92.1%to96.1%, the relative standard deviations (RSD) were1.9%and2.1%(n=3) and the limits of detection (LODs) were1.7μg/L for Cu and0.66μg/L for Co, respectively. The proposed method was applied to determine Cu and Co in medicinal herb samples with satisfactory results. Part3Acid-induced cloud point extraction (ACPE) and preconcentration of heavy metals in medicinal herb samples by flame atomic absorption spectrometry (FAAS) determinationThis method was based on sodium dodecyl sulfate (SDS) and concentrated hydrochloric acid (HC1) were used as extractants, Cu and Cd reacted with1-(2-Thiazolylazo)-2-naphthol (TAN) to give hydrophobic chelates (M-TAN), which were separated and preconcentrated in the SDS phase at room temperature. Additionally, the M-TAN was determined by FAAS without the interference from other heavy metals. Besides, in the given optimized experimental conditions, calibration plots were found to be linear in the range of0.1-5.0mg/L, the linear correlation coefficients were0.9956and0.9966, the recoveries ranged from86.9%to93.8%and the relative standard deviations (RSD) were2.9%and2.1%(n=3) for Cd and Cu. The limits of detection (LODs) were1.5μg/L for Cd and2.6μg/L for Cu, respectively. And the proposed approach was applied to determine Cd and Cu in medicinal herb samples with satisfactory results.