Study Of New Methods For Detection Of Plant Growth Regulators In Vegetables

In this research,A new method for detection of four plant growth regulator?PGRs?residues?forchlorfenuron?CPPU?,thiabendazole?TDZ?,indolebutyric acid?IBA?and naphthaleneacetic acid?NAA??commonly used in vegetables was establishment based on thiol-functionalized polyacrylonitrile nanofibrous membrane used as solid phase extraction adsorbent coupled with ultra performance liquid chromatography-tandem mass spectrometry?UPLC-MS/MS?.The research content is divided into the following two parts:I.Preparation and characterization of thiol-functionalized polyacrylonitrile nanofibrous membranePolyacrylonitrile nanofiber membrane?PAN NFsM?was prepared by electrospinning method,and it got functionalized modification as a base material by amino group?-NH₂?,carboxyl group?-COOH?and sulfydryl group?-SH?.SH-PAN NFsM was selected as the best adsorbent by comparing the adsorption rates of the four types of NFsM to the target substances.The preparation conditions of SH-PAN NFsM were further optimized,thay was the amount of cysteamine hydrochloride and reaction time investigated by the adsorption rate index.As the result,the cysteamine hydrochloride was added at 2.0g,and when reacted togethered with PAN NFsM for 5h in water bath at 80°C,the prepared SH-PAN NFsM had the highest adsorption rate for the 4 PGRs.The diameter of the nanofiber membrane was observed by electron scanning electron microscopy,which increased from 231.3 nm before modification to 283.2 nm after modification.The specific surface area measurement showed that the area of SH-PAN NFsM?11.674 m²/g?was lower than that of PAN NFsM?12.818 m²/g?due to the increased diameter.The elemental analysis showed that the S element newly came up in SH-PAN NFsM with a content of 4.72%,which was equivalent to 1.475 mmol/g thiol group.The Fourier infrared spectrum showed that the new secondary amide and thiol stretching peaks appeared at 3700 cm^-13100 cm^-1?1650cm^-1 and 2750 cm^-1.Detection adsorption rates of SH-PAN NFsM for the four PGRs,it were significantly improved than PAN NFsM.The above results indicated that the sulfhydryl group was successfully modified on the surface of the PAN NFsM.?.Establishment and evaluation of a new method for the determination of 4 PGRs in vegetablesIn this chapter,a new method for detecting four PGRs commonly used in cucumber,mung bean sprouts and bean sprouts with SH-PAN NFsM-SPE-UPLC-MS/MS was established.By calculating the extraction rate and recovery rate,the important parameters such as the volume of organic extraction solvent,the mass of the sample,the volume of the sample solution,the amount of adsorbent,the type and volume of the eluent were optimized.At last,the reusability of NFsM was also taken into consideration.The main research results were as follows:1.5 g homogenized sample was extracted by 1 mL of 1%acetic acid acetonitrile,then it was vortexed and mixed for 1 min.Nextly the sample was centrifuged at 6000 r/min,4°C for10 min.Taking 200?L supernatant to dilute to 3 mL with ultrapure water,a sample solution for solid phase extraction was prepared.5 mg of SH-PAN NFsM was used to adsorb 4 PGRs in the prepared 3 mL sample,finally,200?L of 20%acetic acid-methanol could entirely eluate targets in SH-PAN NFsM,and it was directly detected by UPLC-MS/MS.In addition,the adsorbent SH-PAN NFsM could be reused 6 times.After the series of pretreatment operations,the recovery rate of 4 PGRs could reach ae least 90%.Through methodological evaluation,the detection limit of 4 PGRs in cucumber,mung bean sprouts,bean sprouts was in the range of 0.2² ng/g,and the limit of quantification could be between 0.6⁶ ng/g.Due to the matrix inhibition effect in three vegetable samples,matrix-matched standard curve was made for quantification,which can maintain good linearity in the range of 0.6¹00 ng/g,and the spiked recovery of 4 PGRs could be between 88.94%¹06.42%.The intra-day and inter-day precision were all less than 11.92%,indicating the accuracy,stability and reproducibility of the new method.Compared the newly established method with relevant literatures and National standard methods?GB/T 20770-2008?SN/T 4586-2016?SN/T 2228-2008?,the new method was simpler in operation?small sample usage,no need for nitrogen reconstitution?,lower organic reagents consumption?3.2 mL?,and green economy?the adsorbent can be reused for 6 times?,at the same time,it could ensure the same degree or even better sensitivity and recovery rate.Using the established detection method,a total of 30 samples of cucumber,mung bean sprouts and soybean sprouts were analyzed.The results showed that the detection rate of the 4 PGRs in cucumber was the highest?60%?,and among 4 PGRs,the detection rate of CPPU and TDZ?both 33.3%?were highest,followed by IBA and NAA?both 6.67%?.Besides,the residual concentration of CPPU?7.27 ng/g?was the highest,followed by TDZ?2.37 ng/g?,but the residual concentration was lower than the national maximum residue limit?GB 2763-2016?and EU standard?EU/EC No 62?./2018).