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Novel Approach Towards Mechanical and Thermal Resistant Capillary Microextraction by Sol-Gel Technique in On-Line Combination with High Performance Liquid Chromatography

Piri-Moghadam, Hamed | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45573 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry Scienece
  6. Advisor(s): Bagheri, Habib
  7. Abstract:
  8. In this thesis, a new approach was developed to achieve mechanical and chemical resistant capillary microextraction (CME) in on-line combination with high performance liquid chromatography (HPLC) based on sol-gel technology. This thesis is divided into three chapters:
    First chapter contains of two parts. Overcoming the lack of mechanical stability of the substrate of CME by replacing the fused silica by copper tubings was the main objective of the first part. Self-assembled monolayers technique was employed to functionalize the copper tube followed by chemical bonding of the sorbent on the inner surface of the copper tube by sol-gel technology. The prepared copper tube containing the sorbent was coupled on-line to liquid chromatography for microextraction of polycyclic aromatic hydrocarbons (PAHs). Linear range of 0.01-500 µg L-1 was obtained for all analytes. Limit of detection (LOD) (S/N=3) and limit of quantification (LOQ) (S/N=10) were in the range of 0.005-0.5 µg L-1. Precision of the developed method was also obtained by five consecutive extractions (5 µg L-1) which relative standard deviation percentage (RSD%) in the range of 2.8-8.3 were achieved. Long lifetime of the sorbent was another advantage of the developed methods.
    Second part of chapter one was devoted to the role of precursor and coating polymer in selective sol-gel based sorbents. CME in on-line combination with HPLC was also employed by coating the sorbent on the inner surface of the copper tube. Five precursors along with one coating polymer were used to prepare ten sorbents. The precursors included Tetramethoxysilane (TMOS), 3-(trimethoxysilyl) propylmethacrylate (TMSPMA), 3-(triethoxysilyl)-propylamine (TMSPA), 3-(mercaptopropyl) trimethoxysilane 3MPTMOS, [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane (EPPTMOS) while poly(ethyleneglycol) (PEG) was employed as the coating polymer. Different class of analytes such as triazines, PAHs, estrogens and herbicides were used for evaluation of the prepared sorbents.
    The main goal of the second chapter, included three parts is preparation of selective sorbents by molecularly imprinted xerogels (MIX). The first part is focused on the preparation of MIX for CME of atrazine from aquatic media. In this project, a simple route was developed for preparation of novel selective sorbents by sol-gel technology. TMSPMA was employed as the precursor in sol-gel technique as methacrylate acted as monomer and trimethoxysilyl as crosslinker. Comparison of MIX and NIX (ratio of 10) proved the efficiency and selectivity of the prepared xerogel to the atrazine, template molecule. The LOD and LOQ values for atrazine, ametryn and terbutryn were in the range of 1-5 µg L-1 and 5-10 µg L-1, respectively.
    In the second part preparation of MIX of fentanyl and evaluation of the sorbent in the more complex samples were investigated.The LOD and LOQ valueswere 3 µg L-1 and 5 µg L-1, respectively. The linearity of the analyte was in the range of 5–5000 µg L-1. The LOD value was found to be 3 µg L-1 and the inter- and intra-day RSD% of 5.5 and 6.5 (n= 5) were obtained. For evaluation of the efficiency of the developed sorbent in complex samples, drug-free plasma and urine were used and satisfactory relative recoveries were obtained.
    The third part was dealt with in-situ preparation of polyaniline (PANI) into the sol of EPPTMOS for reduction of the gelation time to increase the selectivity towards the template molecule. Preparation of PANI into the sol of EPPTMOS led to reduction of gelation time from few days to a few weeks. The developed method was employed to prepare the MIX of naproxen. The obtained ratio of 4 for MIX/NIX ratio, showed good selectivity of the prepared sorbent towards naproxen while this ratio was between 1-1.5 for the other analytes. Satisfactory linear range, LOD and LOQ were also obtained. Relative recoveries of 76 % and 94 % were achieved for plasma and urine samples, respectively.
    In the third chapter, electrospinning was employed for preparation of nanofibers and it was focused on the on-line combination of µ-SPE with HPLC was used. The first part was focused on preparation of titania nanocomposites ceramics. Sol-gel technique was coupled to electrospinning system to prepare the titania ceramics nanofibers. Metal/titania composite was prepared to increase the sorption capacity. Precision of the developed method was also obtained by five consecutive extractions at two concentration levels, 30 and 500 µg L-1. The LOD of 0.3 and 2 µg L-1 and LOQ of 1 and 5 were achieved for clobetasol and naproxen, respectively.
    The main objective of the second part of the third chapter was to reduce the diameters of the prepared electrospun nanofibers by assisting auxiliary electrical and magnetic fields. For preparation of nanofibers by magnetic field, a magnetic ionic liquid was added to the desired polymer, polyamide. For evaluation of the prepared sorbents, µ-SPE of imidocloprid, metribuzin, ametryn and chlorpyrifos was used in on-line combination with HPLC. The obtained data revealed that the nanofibers prepared by magnetic field had the highest extraction efficiency. The obtained LODs in the range of 0.4-4 µg L-1 showed the significant efficiency of the prepared nanofibers.
  9. Keywords:
  10. Sol-Gel Method ; High Performance Liquid Chromatography ; Online Capillary Microextraction ; Molecularly Imprinted Xerogels ; Electrospun Nanofibers

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