The Research On Determination Of 10 Organonitrogen Pesticide Residues In Wuyi Rock Tea By High Performance Liquid Chromatography-Tandem Mass Spectrometry

Wuyi rock tea, as the originator of oolong, is one of the Chinese top 10 famous teas, with a long history and a high popularity. Wuyi rock tea could be classified as Zhengyan tea, Banyan tea, and Zhou tea based on the different places of origin. The current product standards of Wuyi rock tea were established in 2006, and only 14 pesticides with the maximum residue limit (MRL) were listed in the standards. Compared to the tea product requirements in "national food safety standard maximum residue limits of pesticide in food" (GB2763) published in 2014,10 organic nitrogen pesticides, such as diflubenzuron, diafenthiuron, cartap hydrochloride, methomyl, and buprofezin are not included in the current product standards. Since the detection of pesticide residues in the Wuyi rock tea was rarely reported, it is urgently required to develop a fast and accurate detection technology to accomplish the analysis of organic nitrogen pesticides in Wuyi rock tea.This thesis have established a novel method to detect 10 organic nitrogen pesticides, such as diflubenzuron, diafenthiuron, and cartap hydrochloride in Wuyi rock tea by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The experimental conditions were optimized, including mobile phase, extracting agent, TPT SPE, the types of eluent and the volume of eluent. The best experimental conditions were obtained with acetonitrile-water (0.1% formic acid) as mobile phase in gradient elution, acetonitrile as extraction agent, the Cleanet-TPT as extraction column and acetonitrile-toluene (3:1, V/V) as elutent buffer. The method of once extraction, once purification and once injection was established for the detection of 10 organic nitrogen pesticides in Wuyi rock tea by HPLC-MS/MS. According to the experimental results,10 liner relationships for 10 pesticide residues in Wuyi rock tea samples were obtained in the range 20-200 ng/mL, and the correlation coefficient R2 were greater than 0.994. The average recoveries of three spiked samples (20、50、100μg/kg) were detected between 72.3-113.6%, and the relative standard deviation (RSD) were determined between 2.8-6.7%. The minimum detection limit was all below the MRL which was required in GB2763-2014 for tea.To understand the distribution of pesticide residues in Wuyi rock teas grown in different areas (shanchang), and in different varieties of Wuyi rock teas, the research of ten pesticide residues in the 10 main planting varieties (Banyan tea), and the research of 10 residues in two varieties of Wuyi rock teas (Shuixian and Rougui) in different shanchang were studied. The results showed that there was less amount of pesticide residues detected in Shuixian, Rougui, Baijiguan, and Tieluohan than that in Shuijingui, Beidou, Queshe, Bantianyao, and Bairuixinag which were planted in the Banyan shangchang. According to the research of the distribution of 10 pesticide residues in Shuixian and Rougui grown in different shanchang, the amount of pesticide residues in Zhou tea shanchang was more than that in Banyan shanchang, and the amount of pesticide residues in Banyan shanchang was more than that in Zhengyan shanchang. For the Wuyi rock tea grown in the same shanchang, the amount of pesticide residues in Rougui was more than that in Shuixian. The amount of pesticide residues in Wuyi rock teas which have been tested was under the MRL value, demonstrating a low level amount of the pesticide residues exsited in Wuyi rock tea currently.