Microwave-assisted extraction of benzoylcyclohexanone and benzoylpyrazole herbicides from agricultural soil

Milaković, Milena (2016) Microwave-assisted extraction of benzoylcyclohexanone and benzoylpyrazole herbicides from agricultural soil. Diploma thesis, Faculty of Science > Department of Chemistry.

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Abstract

The factors that affect the microwave-assisted extraction of the benzoylpyrazole herbicide topramezone and the benzoylcyclohexanone herbicides tembotrione and mesotrione, as well as two mesotrione degradation products (2-amino-4-methylsulfonyl-benzoic acid, AMBA and 4-methylsulfonyl-2-nitrobenzoic acid, MNBA) from agricultural soil (organic carbon content 0.9 %; pH = 7.3) were investigated. The mass concentrations of compounds in soil extracts were determined by high-performance liquid chromatography coupled with an UV diode array detector and calibration with external standards prepared in deionised water. Topramezone, tembotrione, mesotrione and MNBA were efficiently extracted from dry soil with solvent mixture ψ (methanol, 0.1 mol L−1 hydrochloric acid) = 9 : 1 at 60 °C for 5 min with magnetic stirring of suspension at 1 : 6 of soil-to-solvent ratio. The analytical recovery from soil fortified with analytes at mass fractions ranging from 97 to 204 ng g−1 was between 80 % for mesotrione and MNBA and 94 % for topramezone, with a relative standard deviation under 11 %. The limit of detection for all of the analytes was 5 ng g−1. The proposed method is not suitable for the extraction of AMBA from soil. The analytical recovery of all of the compounds from acidic soil (pH = 5.4) was under 50 %, probably as a result of a higher sorption or a higher hidrolysis of neutral herbicide molecules in soil. Reduced selectivity and precision of herbicide determination in soil with 2.9 % of organic carbon content resulted in nearly 60 % of their analytical recoveries. The extraction efficiency of herbicides from wet soil ranged from 60 to 67 %, while MNBA recovery was 95 %. The proposed extraction procedure was optimised for quantitative analysis of topramezone, tembotrione, mesotrione and MNBA in neutral, low humic and dry soil, whereas their analysis in neutral, humic and wet soil should be performed using either internal standard or matrix-matched external standard calibration. The analysis of the elementary and high school chemistry syllabuses with respect to the separation methods of mixtures is given in the methodical part of the diploma thesis. Also, an high school chemistry lesson that deals with extraction and chemical balance and is based on guided inquiry learning strategy was designed and commented in details.

Item Type: Thesis (Diploma thesis)
Keywords: liquid chromatography, mesotrione, microwave-assisted extraction, soil, tembotrione, topramezo
Supervisor: Stipičević, Sanja and Judaš, Nenad
Date: 2016
Number of Pages: 97
Subjects: NATURAL SCIENCES > Chemistry
Divisions: Faculty of Science > Department of Chemistry
Depositing User: Branka Maravic
Date Deposited: 06 Sep 2016 15:32
Last Modified: 06 Sep 2016 15:33
URI: http://digre.pmf.unizg.hr/id/eprint/5039

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