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Preparation of Herbal Biomass as Extractive Phases for Trace Determination of Pesticides

Keikavousi Behbahan, Arnavaz | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56074 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Bagheri, Habib; Mahdavi, Vahideh
  7. Abstract:
  8. The main approach of this thesis is to study the performance and efficiency of agricultural biomass derived extractive phases in sample preparation methods. In this regard, different types of agricultural biomasses and various important factors in the production of biochar from biomass were studied by two physical and chemical methods. Accordingly, different types of biochars have been made and applied in different extraction setups along with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and gas chromatography-electron capture (GC-ECD) to detect agricultural pesticides. Also, validated developed methods were used to investigate the safety of some highly consumed agricultural products. Since the selected real samples were based on real case studies and some pesticides could be detected (due to the efficiency of developed methods), risk assessment studies could also be performed on studied real samples which produced valuable information. In the first work, the main purpose was to study the effective factors in physical-chemical activation as an effective method in making biochar. In this regard, four main factors including: activation temperature, repetition of activation, material used in chemical activation (acid, base or metal salt) And the weight ratio of chemical modifier to biomass were evaluated. Since these parameters are highly dependent to each other, they cannot be studied separately. To investigate these four factors at the same time, the Taguchi experimental design method was used and sixteen unique biochars were prepared from banana peel as the source biomass. The prepared biochars were used in a simple extraction method called pipette tip-µ-solid phase extraction (PT-µ-SPE) to extract twelve widely used agricultural pesticides. The diverse polarity and functional groups in the target pesticides led to the comprehension of various interactions between biochars and target analytes. Also, useful information regarding the characteristics of the prepared biochars were obtained. PCA biplot and t-test were used to choose the biochar with the best performance to extract target pesticides. Finally, the biochar activated once at 450˚C by acid as chemical modifier was selected as the optimum sorbent and evaluated through different characterization methods. Afterward, effecting parameters on the extraction method including: desorption solvent, desorption volume, pH of extraction solution, extraction cycle and desorption cycle were optimized using one variable at the time (OVAT) procedure. Afterward, the figures of merit were studied and the limit of detection (LOD) values of 0.03–10 μg L-1, limit of qualification (LOQ) values of 0.1-100 μg L-1, linear dynamic range (LDR) of 0.1-200 μg L-1, and a range of RSD values of 5.3–19% were obtained. Eventually, five fruiting vegetables were analyzed and screened for their possible contaminations. Among the tested pesticides, chlorpyrifos, diazinon, malathion, phosalone, propargite and thiophanate-methyl were detected in eggplant, sweet pepper, zucchini and tomato.In the second work, the effect of chemical modifier with specific framework on the properties of biochar derived from walnut shell was evaluated. For this purpose, a nickel-based metal-organic framework (Ni-MOF) was used as the chemical modifier, and biochars with different weight ratios of Ni-MOF:biomass from 10 to 50% w/w were prepared. The prepared biochars were used as sorbents in PT-µ-SPE setup to extract twenty pesticides. The selected pesticides are widely used in the cultivation and storage of wheat as an agricultural product with the highest per capita consumption in Iran. The results clearly showed the positive effect of Ni-MOF as the chemical modifier on the extraction efficiency of target pesticides. The characterizations including SEM and BET clearly showed the increase in the porosity of prepared biochars due to the chemical modification, which resulted to the extraction efficiency enhancement. Eventually, the modified biochar with 50% w/w of Ni-MOF:walnut shell was selected as the optimum sorbent. Afterward, effecting parameters in extraction setup including desorption solvent, desorption volume, extraction flow, desorption flow, extraction time and desorption cycle were optimized through the OVAT procedure. Evaluation of figures of merit resulted to the LOD and LOQ in the range of 0.01–12.1 μg L-1 and 0.03–40.5 μg L-1, LDR in the range of 0.5-1000 μg L-1 and precision in the range of 2.4–28.3 %. This method was applied for the analysis of 29 wheat samples and the results indicated the presence of some target pesticides in the analyzed samples. The risk assessment study demonstrates that the contaminated wheat samples cannot cause non-carcinogenic harm to adults but might have an impact on children.In the third work, a comparison was made between the biochars prepared from the biomass of different nutshells including pistachio, almond, walnut and hazelnut in the extraction of eleven agricultural pesticides from water samples. Also, two novel biochar derived from neem tree nut shell biomass and its chemical modification with multi-walled carbon nanotubes (MWCNT) and urea was prepared and compared with other nutshell biochars. To apply the prepared biochars in thin film microextraction (TFME) setup, various composites of biochars-polyamide 6 were prepared and used to extract target pesticides from water samples. The extraction efficiency results demonstrated a trend similar to the made biochars’ porosity, except for neem tree nutshell biochar (NTNSB), which could be attributed to the possible functional groups on its surface. Also, the chemical modification of neem tree nutshell with MWCNT and urea resulted to the hydrophilicity increment of the prepared biochar through better extraction of relatively polar analytes by this sorbent. Eventually the NTNSB-polyamide with 30% w/w of biochar was chosen as the optimum composite. Afterward, effecting parameters on TFME setup including desorption solvent, desorption volume, shaking rate, desorption condition, extraction and desorption time were optimized through the OVAT procedure. Method evaluation resulted to a LOD range of 0.003-0.5 μg L-1, a LOQ range of 0.01-1.6 μg L-1 and a LDR range of 0.05-50 μg L-1. Accordingly, precision was studied and a range of 5.7-24.5% was obtained. The evaluated method was used for the extraction of 31 ground, surface, and tap water samples. The results showed that four groundwater samples were contaminated and two target pesticides (4,4´-DDE and p,p´-DDD) had higher concentration than the limited dose in water
  9. Keywords:
  10. Biochar ; Chemical Activation ; Physical Activation ; Solid Phase Microextraction ; Agricultural Products ; Gas Chromatography ; Liquid Chromatography ; Herbal Biomass

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