| Dendrobium candidum(Dendrobium officinale Kimura et Migo)is a perennial herb of Orchidaceae,the rhizome is used as medicine,is a precious traditional Chinese medicine in China,which has the effect such as improve human immunity,enhance memory,anti-aging and anti-tumor,and so on.In recent years,with the people's attention of Chinese herbal medicines,Dendrobium candidum is increasingly demanded year by year.At the same time,the quality and safety of Dendrobium candidum product(especially pesticide residues in Dendrobium candidum)have been getting more attention.In this paper,using Dendrobium candidum as the object,analytical method of pesticide residues in Dendrobium candidum has been established,which provided detection means for the real sample;degradation dynamics of difenoconazole,myclobutanil and tebuconazole in Dendrobium candidum were studied,which provided the basis for the rational use of these pesticides in Dendrobium candidum cultivation;the residue levels of organochlorine in Dendrobium candidum of Zhejiang province were studied.The main results were summarized as follows:(1)A method using dispersive solid-phase extraction(d-SPE)clean-up followed by HPLC-MS/MS has been developed for the determination of 8 organophosphorus pesticides in Dendrobium candidum samples.The samples were soaked by water and then homogeneously extracted with acidified acetonitrile.The extracts were cleaned up by d-SPE using PSA,separated on a Waters Atlantis T3 column and analyzes by HPLC-MS/MS under multiple reaction monitoring mode.Matrix matching curve external standard method was using for quantification.The method shows excellent linearities(r>0.997)for all compounds in a certain concentration range.The recoveries at three spiked levels of 10,50 and 100 ? g/kg ranged from 75.9 to 117.8% with the relative standard deviations(n=6)from 2.1 to 12.3%.The limit of detection and the limit of quantification of 8 pesticide residues were in the range of 0.15~5.47 ? g/kg and 0.84~8.52 ? g/kg,respectively.The method has been proven to be simple,quick,sensitive and suitable for determination of organophosphorus pesticides in fresh Dendrobium candidum samples.(2)A method using solid-phase extraction(SPE)clean-up followed by GC-ECD has been developed for the determination of 16 organochlorine pesticides in Dendrobium candidum samples.The sample was extracted with acetonitrile and cleaned-up by florisil column.The analytes were analyzed by GC-ECD and quantified with external standard.The result showed that the average recoveries of all the analytes at three levels(0.005 mg/kg,0.025 mg/kg and 0.05 mg/kg)were between 74.8%~114.3% with relative standard deviations ranged from 1.3~13.6%.The limits of detection were 0.0001 mg/kg ~ 0.0020 mg/kg,and the limits of quantity were 0.0012 mg/kg ~0.0094 mg/kg.(3)The residue dynamic and final residues of difenoconazole,myclobutanil and tebuconazole in stalk and leaf of Dendrobium candidum were studied through the field experiment.The results showed the degradation of the three pesticides in Dendrobium candidum followed the first-order kinetics equation.The half-lives of difenoconazole,myclobutanil and tebuconazole in the stalk of Dendrobium candidum were 9.1 d,8.3 and 8.6 d,and in the leaf of Dendrobium candidum were 8.7 d,9.0 d and 8.3 d.When the three pesticides were applied twice or three times at recommended concentration,the final residues of three pesticides in Dendrobium candidum were all below 0.5 mg/kg that harvested more than 30 days after the last application.(4)Levels of organochlorine pesticide contents in Dendrobium candidum from mian production regions of Zhejiang province were measured.The results show that,different areas have detected different levels of pesticide residues.Heptachlor is the biggest contribution to the detection of pollutants with the detection rate of 82.8%,but it don't exceed the MRL value.Dicofol,o,p'-DDT,chlorothalonil and quintozene also were detected with different degree. |
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