Study on decline and residue of thidiazuron in grape and soil by high performance liquid chromatography-tandem mass spectrometry

Abstract: 【Objective】To understand the dynamic degradation and final residue of thidiazuron in grapefruit and grapery soil, respectively. We propose a high performance liquid chromatography-tandem massspectrometry (HPLC-MS/MS) method to detect thidiazuron in grape fruit and grapery soil. The degrada⁃tion of grape in the fruit followed the first order kinetic equation (CT=C0ekT). Therefore, we compute thehalf-life (T1/2) in the fruit of this plant growth regulators based on that equation. These results will provideguidance on the proper and safe use of this plant growth regulator for grape fruit.【Methods】The trialswere conducted in experimental fields where located in Henan province and Jiangsu province for past twoyears. In degradation dynamics experiment, six field plots formed one set, each with two grapevines. 0.1%thidiazuron wettable powder formulations (200 times dilution) were soaked to grape cluster (the half of themature individuals) and each experiment was conducted in triplicate. The detailed method is described asfollows. Firstly, the untreated plots were soaked with water under control. Secondly, the representativesamples (grape fruit) were collected at 2 h, 1 d, 2 d, 3 d, 5 d, 7 d, 10 d, 14 d, 21 d and 28 d after thidia⁃zuron treatment. Thirdly, the samples were placed in a freezer with - 20 ℃ after sample preparation.Fourthly, the pesticide residue in the sample was collected after two hours on the day of applying was setas the original reside, the residue levels in the rest samples were compared with the original residue to getthe degradation rate. Lastly, the dissipation equation was fitted to the first order kinetics equation usingthe SigmaPlot software. In final residue experiment, according to the maximum recommended dose and1.5 times of the maximum recommended dose, 0.1% thidiazuron wettable powder were soaked to grapecluster 1 or 2 times with an interval of 10 days, grape samples and grapery soil were collected 7, 14 and 21 d after the last treatment. The Pretreatment methods of thidiazuron residue determination: A 10 ggrapery soil or grape fruit was weighed and put into centrifuge tube. A 5 mL ultra pure water and 20 mL acetonitrile was added into grapery soil samples, a 20 mL acetonitrile was added into grape samples. Aftershaken vigorously by Multitube Vortexer for 15 min, 3 g NaCl was added into centrifuge tube and themixture was vortexed for 1 min. The sample solutions were separated by centrifuging with 6 000 r·min^-1 for 5 mins, then the supernate filtered with 0.22 μm syring filter for HPLC- MS/MS analysis.【Results】Inthe concentration range of 0.01-1.0 mg·L^-1, the matrix-matched calibration curves showed good linearitywith correlation coefficients 0.999 6. The average recoveries of thidiazuron in the grape and soil werefound between 84% and 108% at 0.01-0.50 mg·kg^-1, with relative standard deviations (RSD) of 0.5%-1.9%. The limit to quantification (LOQ) was 0.01 mg·kg^-1. The efficiency of our proposed method in mea⁃suring trace levels of thidiazuron was monitored by analyzing the samples collected from the field trials. Indegradation dynamics experiment at Henan and Jiangsu experiment fields, the original residue of thidia⁃zuron in the grape fruit were 0.039 1-0.017 4 mg·kg^-1, the thidiazuron degradation rate found 7 d aftertreatment were 100%, 100%, 100%, 66.4% in grape fruit for 2014 and 2015. The half-life (T1/2) of thidia⁃zuron in grape fruit from Henan in 2014 and 2015 were 1.7 d and 1.7 d, and from Jiangsu were 0.8 d and5.7 d. The final residue test showed that thidiazuron was readily degraded in grape and the final residue ofthidiazuron in the grapery soil was less than in the grape. In 7, 14 and 21 d after the last pesticide soak,95.1% of the grapery soil testing data is below LOQ (0.01 mg·kg^-1), while the grape is 70.1% below LOQ (0.01 mg·kg^-1), the highest residue in the grape and grapery soil of all final residue test date was 0.024 7mg·kg^-1 (2014, Jiangsu high-dose group, twice treatment, 7 d), 0.020 0 mg·kg^-1 (2015, Henan low-dosegroup, twice treatment, 14 d), respectively.【Conclusion】The result indicated that thidiazuron is readilydegreaded in grape and is safe to environment and soil. In addition, the thidiazuron maximum residue lim⁃it (MRL) in grape is 0.05 mg·kg-1 and the safety period of 0.1% thidiazuron wettable powder is 14 d.