The Preparation Of Novel Stir Bar Sorptive Extraction Coatings And Their Applications In Environmental And Food Analysis

The rapid development of economy greatly improves human’s daily life, but it also brings about several problems, such as environmental pollution, public health and food safety. Thus, the analysis of contaminants at trace levels is of great significance for the monitoring of environmental and food security, which is also a great challenge for the analysts. Direct quantification of trace contaminants in real-world samples is often difficult even by the use of modern analytical instrumental methodology, due to the complex sample matrix and extremely low levels of target analytes. Therefore, suitable sample pretreatment techniques are often required prior to analysis for the enrichment of target analyte and separation of complex matrices. Stir bar sorptive extraction (SBSE) was developed in1999by Baltussen and co-workers. It possesses many merits such as high enrichment factor, good reproducibility, high adsorption capacity, high recoveries and solvent-free, and has been applied to the analysis of various analytes in environmental, food and biological samples. But there were several factors strictly limited the development of SBSE, including (1) commercial coating is very limited, expensive, with poor selectivity;(2) it is lack of novel coatings, extraction modes and devices which are suitable for the analysis of polar compounds or the simultaneous analysis of compounds with different properties,(3) it is difficult to be automated. Therefore, the preparation of novel coating with high extraction efficiency, selectivity, long lifetime, which is suitable for the analysis of polar compounds and simultaneous analysis of different compounds, is urgent and significant for the further development of SBSE and its application.The aim of this dissertation is to prepare new polar SBSE coatings for the preconcentration of polar compounds or simultaneous preconcentration of various compounds with different polarity, and to establish SBSE-gas chromatography/high performance liquid chromatography (GC/HPLC) methods for the analysis of organic contaminants in environmental and food samples. The major contents of this dissertation are described as follows:(1) Polythiophene (PTH) was synthesized by chemical oxidative polymerization method, and PDMS/PTH coated stir bar was prepared by sol-gel technique. This work introduced electron-rich organic polymer (PTH) to SBSE coating, which significantly benefit the extraction of target organophosphorus pesticides (OPPs) by conjugation. Compared with PTH fiber coating prepared by electrochemical polymerization method, the prepared PDMS/PTH coating by sol-gel method possesses many advantages such as simplicity, high coating capacity and mechanical strength. Based on it, a method of polydimethylsiloxane/(PDMS)/PTH coated SBSE coupled to liquid desorption (LD)-large volume injection(LVI)-gas chromatography-flame photometric detection (GC-FPD) was proposed for the determination of five interest OPPs (phorate, fenitrothion, malathion, parathion and quinalphos) in environmental water samples. Under the optimal conditions, the limits of detection (LODs, S/N=3) were found to be in the range of0.011-0.038μg/L for the five target OPPs, and the enrichment factors were varying from56.7to80.9-fold (theory enrichment factor was100-fold). The results showed that the PDMS/PTH coating has high extraction efficiency and fast extraction dynamics for target OPPs and the limits of quantification met the requirements of real sample analysis.(2) An amino modified multi-walled carbon nanotubes/polydimethylsiloxane (multi-walled carbon nanotubes-4,4’-diaminodiphenylmethane/polydimethylsiloxane, MWCNTs-DDM/PDMS) was synthesized, and utilized as a novel coating for SBSE of seven phenols(including phenol,2-chlorophenol,2-nitrophenol,4-nitrophenol,2,4-dimethylphenol, p-choro-m-cresol and2,4,6-trichlorphenol)in environmental water and soil samples followed by high performance liquid chromatography-ultraviolet (HPLC-UV) detection. Compared with the MWCNTs-COOH/PDMS coated stir bar, the prepared MWCNTs-DDM/PDMS coated stir bar exhibited better extraction efficiency for the target phenols. And the preparation reproducibility of MWCNTs-DDM/PDMS coated stir bars was also investigated with the relative standard deviations (RSDs) ranging from4.7to11.3%(n=9) in one batch and from4.8to13.9%(n=8) among different batches, which shows that good reproducibility was obtained for the preparation of MWCNTs-DDM/PDMS coated stir bars. Under the optimal conditions, the proposed MWCNTs-DDM/PDMS-SBSL-LD-HPLC-UV provided LODs of0.14-1.76μg/L for target phenols, and was successfully applied for the analysis of target phenols in environmental water and soil samples.(3) Poly(dimethylsiloxane)/β-cyclodextrin/divinylbenzcne (PDMS/β-CD/DVB)-coated stir bar was prepared by sol-gel technique, and a method of PDMS/β-CD/DVB SBSE combined with HPLC-UV detection for the determination of four estrogens(17-β-Estradiol, dienestrol, diethylstilbestrol and hexestrol) was proposed. The influence of the coating composition on SBSE of target estrogens was investigated by an orthogonal experiment design, and the optimal PDMS/β-CD/DVB coated stir bar was obtained.The addition of β-CD and DVB in the coating increased the extraction efficiency of target estrogens through π-π conjugation and "inclusion" interaction. The prepared PDMS/β-CD/DVB coated stir bar has many advantages such as simplicity, good reproducibility, long lifetime (more than50 times) and suitable for the complex food sample analysis.(4) Three kinds of metal-organic frameworks (MOFs, MOF-5, MOF-199and IRMOF-3) were introduced in SBSE and novel PDMS/MOFs (including PDMS/MOF-5, PDMS/MOF-199and PDMS/IRMOF-3) coated stir bars were prepared by sol-gel technique. These PDMS/MOFs SBSE coatings were critically compared with self-prepared/commercial PDMS SBSE coating for the extraction of seven target estrogens (17-β-estradiol, dienestrol, diethylstilbestrol, estrone,4-t-octylphenol, bisphenol-A and17a-ethynylestradiol), and the results showed that PDMS/IRMOF-3exhibited highest extraction efficiency, probably due to the match of cavity size and the function of amino group. Based on the above facts, a novel method of PDMS/IRMOF-3coating SBSE-HPLC-UV detection was developed for the determination of seven target estrogens in environmental water samples. The high extraction efficiency and rapid extraction dynamics of the PDMS/IRMOF-3coating for the target estrogens demonstrates a great application potential of the PDMS/MOFs coating in SBSE with good selectivity.(5) A MOFs (Al-MIL-53-NH2) was synthesized by hydrothermal method, and a PDMS/Al-MIL-53-NH2coated stir bar was prepared with sol-gel technique. A new method of PDMS/Al-MIL-53-NH2SBSE combined with HPLC-fluorescence (FLD) for the determination of15polycyclic aromatic hydrocarbons (PAHs) in environmental water samples was proposed. The prepared PDMS/Al-MIL-53-NH2coated stir bar exhibited good preparation reproducibility and mechanical strength, and it can be reused for more than40times. The developed method is characterized with LODs, high extraction efficiency and wide linear range for the target PAHs, and shows a good application potential for the analysis of PAHs in various environmental samples.(6) Polyaniline (PANi), which was synthesized by chemical oxidative polymerization method, was mixed homogeneously with hydroxy-multi-walled carbon nanotubes (MWCNTs-OH) with grinding, and the mixture was employed for the preparation of a novel composite coating by adhesion method. The extraction performance of PANi/MWCNTs-OH composite coating for different kinds of analytes with different polarity was investigated, and a new method of PANi/MWCNTs-OH-SBSE-HPLC-UV was proposed for the simultaneous detection of polar, midium polar and apolar compounds(phenols, non-steroidal anti-inflammatory drugs, polychlorinated biphenyles) in environmental water and sediment samples. The developed method has many advantages, such as low LODs, high extraction efficiency for each analyte, and provides a new idea for simultaneous preconcentration and analysis of diffient polarity compounds by use of one single stir bar with one kind of coating in SBSE.