Abstract
The contamination of food commodities with pharmaceuticals and mycotoxins has drawn attention globally due to their environmental and human health risks. Different extraction procedures and adsorbents have been exploited for their removal in various matrices, and the improvement in these extraction procedures has become a recurring topic in research especially on emerging pollutants. Strict regulations and continued monitoring of food commodities through efficient analysis are necessary for successfully controlling the growing threat and impact of these contaminants, which are one of several reasons why novel approaches are constantly required. This research describes the synthesis, characterization, and application of a novel magnetic nanocomposite (Fe3O4@SiO2@GO@[BMIM]BF4 (1-butyl-3-methylimidazolium tetrafluoroborate)) as an adsorbent for magnetic solid phase extraction (MSPE) of mycotoxins and pharmaceuticals from water and beverages followed by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis. The research was conducted in four phases herein, presented as chapters (Chapters Four through to Seven).
The key goals of the first phase of the research were (i) synthesis and characterization of the magnetic nanomaterials (Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@GO and Fe3O4@SiO2@GO@[BMIM]BF4, (ii) demonstrate the adsorption of methyltheobromine from water using Fe3O4@SiO2@GO@[BMIM]BF4 nanocomposite. In this experiment, the nanomaterials were successfully synthesized and characterized using various instrument. The central composite design approach with four factors was used in the design and optimization of the experimental conditions. The adsorption mechanism and kinetic models were performed, and Liu model best fitted the obtained experimental data with R2 of 0.9963 followed by Sips (0.9959), Freundlich, Radke-Prausnitz, Redlich-Peterson, with R2 values of 0.9954, and Temkin (0.9950), respectively. The thermodynamic study revealed spontaneous adsorption at all studied temperatures and the adsorption kinetics followed the Elovich model and pseudo-second-order kinetics. Based on these results, it is evident that the novel Fe3O4@SiO2@GO@[BMIM]BF4 material can be applied as an adsorbent for the removal of methyltheobromine (methyltheobromine was chosen as a model pollutant because it is considered an indicator of the presence of pharmaceutically active compounds in the environment) and beverages.
In the second phase of this study, a method for magnetic dispersive solid-phase microextraction followed by an UHPLC-MS/MS analysis was developed and validated for three pharmaceuticals in fruit juice samples. This phase looks at the extraction of pharmaceuticals from fruit juice and its applicability in real fruit juices samples. The Box-Behnken Design (BBD) approach was applied for the experimental design and the optimization of the extraction parameters. The extraction method was successfully developed, optimized, and validated, with satisfactory recovery values of 95.5 to 98.1% (acetaminophen and caffeine) and 8.1% (tetracycline). The recovery values were compared with conventional methods. With a good linearity R2 of 0.999 for all the analytes, the method's calibration levels ranged from 39.06
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to 5000.00 ng/mL. The LOD and LOQ values ranged from 38.18 to 88.2 ng/mL and 39.94 to 265.0 ng/mL, respectively. A relative standard deviation (RSD) value of <7% (caffeine and acetaminophen) and >20% (tetracycline) was obtained. The applicability of the developed method was evaluated for these pharmaceuticals in fruit juice samples. The results revealed that the fruit juices were free of these pollutants. The Fe3O4@SiO2@GO@[BMIM]BF4 material was reused at least ten times. The extraction efficiency of Fe3O4@SiO2@GO@[BMIM]BF4 was compared with Fe3O4@SiO2@GO and the findings revealed no strong difference in their recovery values.
The third phase of the study focused on the use of Fe3O4@SiO2@GO@[BMIM]BF4 for the simultaneous extraction of nine mycotoxins from craft beer using MSPE. The BBD model with four factors was adopted to model and optimize the experimental conditions. The model fit R2 ranged from 76.95 to 94.93%, linearity (R2 of 0.997 to 0.999), LOD (1.43 and 3.20 ng/mL) and LOQ (1.64 and 9.62 ng/mL), respectively. High matrix effects (-68 to 310%) and low recovery values (0.44 to 26.09%) were obtained for all the mycotoxins (these low recoveries could be because of the analytes binding very strongly unto the adsorbent and as such, the analytes could not be efficiently eluted even when the elution process was optimized). The method (MSPE) was further compared with LLE and QuEChERS methods using beer samples that gave better recovery values (36.25 to 76.01%).
The fourth part of this research work describes the extraction of six emerging mycotoxins from beer using MSPE followed by UHPLC-MS/MS analysis. A similar optimization procedure to that of the previous experiments was performed. The study reported model fit R2 ranging from 75.23 to 91.40, linearity R2 >0.999, LOD (1.40 to 4.10 ng/mL) and LOQ (1.70 to 12.4 ng/mL) for all the analytes studied. High matrix effects were noted in the study with low recoveries (6.51 to 28.52%), as such, the method (MSPE) was performed using water and better recoveries (4.31 to 83.1%) were obtained. QuEChERS and LLE methods were compared with the MSPE in beer. The findings revealed that QuEChERS showed better performance. The Fe3O4@SiO2@GO@[BMIM]BF4 was further compared with Fe3O4@SiO2@GO and the results obtained likewise showed low recovery values (12.20 to 29.65%). Due to the low recovery values obtained by our extraction method (MSPE) in Chapters Six and Seven, no further experiments were conducted on the method development and validation.
In conclusion, this study advances environmentally friendly analytical methods to enable bioanalysts and mycotoxicologists in the field of analytical chemistry and mycotoxicology to extract these pollutants conveniently and successfully from various food commodities and other matrices without utilizing large volumes of hazardous and costly organic solvents.
Keywords: Emerging pollutants, magnetic nanomaterial, magnetic solid-phase extraction, water, beverages, and UHPLC-MS/MS.