Browsing by Author "Ahmed Hussen"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Development of Microfluidic Paper Based Analytical Devices (Μ-Pad) for the Determination of Organophosphate and Carbamate Pesticides from Environmental Samples
    (Addis Ababa University, 2023-06) Sheleme Beshana; Ahmed Hussen
    This thesis focuses on the development of microfluidic paper-based analytical devices (μ-PADs) and sample preparation techniques, namely dispersive liquid-liquid microextraction (DLLME) and the combination of QuEChERS (quick, easy, cheap, effective, rugged, and safe) with DLLME for colorimetric determination of organophosphate (OP) and carbamate (CM) pesticides from water and lettuce samples. In the colorimetric quantification, the yellow color is generated by the interaction between acetylcholinesterase (AChE), acetylthiocholine iodide (ATChI), and 5, 5- dithiobis- (2-nitrobenzoic acid) (DTNB). The digital image of the yellow color was captured and analyzed using a Canon scanner and ImageJ software, respectively. Key experimental conditions (concentrations and volumes of AChE, ATChI, and DTNB, incubation time, storage stability, and image capturing time) were systematically optimized using a univariate approach. Under optimized conditions, the method showed a wide linear range (1-16 mg L-1), repeatability (3-5% RSD), and intermediate precision (7-10% RSD), and robustness (≤ 1.85% RSD), with R2 ≥ 0.9945. Limits of detection (LOD) were in the range of 0.24-0.33 mg L-1. An acceptable mean recovery (87-94%) was observed at a 1 mg L-1 fortification level. Following that, the μ-PAD operational parameters (reagent concentrations and volumes) were optimized using multivariate techniques based on the Box-Behnken design (BBD). The analysis of variance revealed that high regression and fitting values were obtained between the experimental and predicted responses at a 95% confidence level. Satisfactory linearity (R2 ≥ 0.9990) in the range of 0.5-16 mg L-1, LOD (0.12-0.17 mg L-1), repeatability (3.75-7.98% RSD), intermediate precision (7.15-10.98% RSD), and accuracy (78-97%) were achieved. The results of the univariate and multivariate optimization were compared and found that the multivariate optimization requires a much lower concentration of the reagents and improved LOD values of the univariates by 29-64% for the studied pesticides. Therefore, the multivariate approach has been demonstrated to be more efficient and effective than the univariate approach. For further improving sensitivity, the μ-PAD was coupled with an enrichment method called DLLM. The experimental parameters (volume of hexane and acetone, extraction time, and salt amount) were optimized using response surface methodology (RSM). The enrichment factors (EF) and LOD values were found in the range of 317-1471 and 0.17-0.41 μg L-1, respectively, which is below the maximum residue limits of EU for drinking water. The matrixmatched calibration curve showed a wide linear range (0.625-40 μg L-1) with R2 ≥ 0.9968. The obtained extraction recovery varied from 79-97% with repeatability (2.21-6.01% RSD) and intermediate precision (5.60-10.41% RSD). Thus, the proposed method is low cost, easy to operate, efficient, and sensitive, showing great potential for the determination of pesticides in water samples. Finally, the combination of QuEChERS, DLLME, and a μ-PAD was developed for the extraction, preconcentration and quantification of target analytes from lettuce samples, respectively. RSM using Plackett-Burman and central composite design were used for the screening and optimization of significant factors, respectively. The matrix-matched calibration curves held excellent linearity (R2 ≥ 0.9988) in the range of 0.01-0.64 mg kg-1. The EFs and LODs were 21-31 fold and 0.006-0.009 mg kg-1, respectively. The recoveries were in the range of 79-97% and good precision was obtained with RSD below 11%. Thus, the experimental results revealed that the QuEChERS-DLLME method is suitable for the routine pesticides analysis from lettuce vegetables in terms of high accuracy, precision, and efficiency.
  • No Thumbnail Available
    Item
    Major Problems Contributing To Students Absenteeism in Secondary School of Zone One Afar Region
    (Addis Ababa University, 2018-10) Ahmed Hussen; Fekadu Mulugta
    The objective this study was to assess the major problems to student’s absenteeism in government general secondary schools in zone one afar region. More specifically, the research determined the current problems of students’ absenteeism in the study areas, identify the major problems influencing student’s absenteeism, and gauge the effects of absences on academic performance of students. The study was a descriptive survey research design where questionnaires, interviews, focused-group discussion and document analysis were used to collect both qualitative and quantitative data. Systematic random sampling method was employed to select the sample schools. While simple random sampling technique was used to select sample students, teacher, PTAs. Student’s parents, principal werda experts the researcher also used to a systematic random sampling of the population and then determined 130 samples of students. Data were both primary and secondary sources using questionnaire, FGD, interview and document analysis. The major problems of the study were personal factors, family factors, school factors, recreational factors and individual factors. The major effects that respondents identified were poor academic performance, wastage of learning time, poor class and school performance, dropping out of school, poverty to the individual and family in future, involvement with delinquent behaviour, family instability, social maladjustment and insecurity in the family. Finally, recommendations have been forwarded and further studies have been recommended.
  • No Thumbnail Available
    Item
    Zr-BDC MOF as a Sustainable Catalyst for Efficient Hydrolysis of Lignocellulosic Biomass
    (Addis Ababa University, 2023-12) Getahun Getachew; Ahmed Hussen; Abi Tadesse
    Lignocellulosic biomass, such as plant matter and agricultural residues, is a major source of renewable organic carbon on our planet. Of this lignocellulose, 40–50% is composed of cellulose that serves as a valuable feedstock for the production of fuels, chemicals, and various industrial applications. Cellulose can be converted into glucose through a process called hydrolysis. The hydrolysis of cellulose using homogenous acids is known to have drawbacks due to the generation of a large amount of toxic and corrosive wastes, making the use of heterogeneous catalysts like metal organic frameworks (MOFs) crucial for eco-friendly cellulose conversion. In this study, Zr-BDC MOF was synthesized sustainably using water as the sole green solvent, at room temperature, and without modulation. The as-synthesized Zr-BDC MOF exhibited a semi-crystalline structure with desirable properties such as a specific surface area of 380.367 m2/g, a pore volume of 0.55cm3 and a pore radius of 13.24 Å. The evaluation of this MOF as a solid-acid catalyst for the hydrolysis of lignocellulosic biomasses, specially Sugarcane bagasse and Pineapple peels was conducted for the first time in this study. Under optimum conditions, a mixture of 4 g biomass (Sugarcane bagasse or Pineapple peels) and 0.8 g Zr-BDC MOF in 100 mL distilled water was hydrolyzed at 130 oC for 4 h. The hydrolysis process yielded 0.60 mg/mL and 2.044 mg/mL of total reducing sugar (TRS), mainly glucose, from the hydrolysis of Sugarcane bagasse and Pineapple peels, respectively. These promising results demonstrated the potential of Zr-BDC MOF as an alternative catalyst for the hydrolysis of lignocellulosic biomass, enabling the conversion of cellulose to glucose for bioethanol production. The use of Zr-BDC MOF offers economic feasibility and environmental friendliness, addressing the challenges associated with homogeneous acid hydrolysis. Furthermore, this study can serve as a benchmark for future research on catalytic application of MOFs in biomass conversion to glucose for bioethanol production.