Application Of Salt-assisted Graphene Oxide Dispersive Solid Phase Microextraction For Analysis Of Organic Pollutants

Graphene, as a new form of carbonaceous nanomaterial, has attracted much interest and intensive research due to its inspiring physical and chemical properties. Compared to those traditional carbonaceous nanomaterials such as fullerene and carbon nanotubes, graphene possesses a number of advantageous characteristics, among which superior specific surface area is particular fascinating along with the two-dimensional planar structure and π-electron conjugated system. Owing to these, graphene has excellent adsorption properties, thus endows it with great application potential in sample pretreatment. Graphene oxide(GO), as the oxydate of graphene, not only contains the original properties of graphene, but also holds a number of unique characteristics. For example, graphene oxide can be uniformly dispersed in water because of its oxygen containing groups on surface. These features give a possibility that graphene oxide can be used in environment sample analysis, especially water samples.Environmental sample analysis is the basis of investigation and control of environmental contaminants. So far, sample pretreatment is still the bottleneck of environmental sample analysis. Sample pretreatment process requires effective extraction and enrichment of target analyte from the complex sample matrix, and adsorbent material with high efficiency and selectivity is the key factor. So developing fast, sensitive and environmentally friendly pretreatment technology is of great urgency.In the present work, we investigated a novel salt-assisted graphene oxide dispersive solid phase microextraction technology, and further studied its application in chromatographic analysis. The main contents are as follows:(1) Malachite green and crystal violet, which all belong to the Triphenylmethane dyes, were selected as the target analytes of this work. And they were pretreated using the established salt-assisted graphene oxide dispersive solid phase microextraction. Finally these two kinds of contaminants in environmental water samples were detected successfully combined with high performance liquid chromatography. This newly developed technology possessed advantages such as simple manipulation, fast extraction kinetics, environmentally friendly. A hypothetical synthesis mechanism was also provided during the experiment, and we further optimized the key parameters including adsorption conditions, type of the eluent and chromatographic conditions. Coupled with salt-assisted GO-DSPME, high performance liquid chromatography(HPLC) could be used for sensitive detection of MG and CV with the detection limits down to 1.7 and 0.3 ng·mL-1 for MG and CV, respectively. Satisfactory extraction reproducibility was obtained(RSD, 1.8% for MG and 3.8% for CV, n=5). The proposed method has been successfully applied to detect MG and CV in real water samples, and the recoveries were ranged from 89.7% to 116.4%.It was demonstrated that graphene oxide had a capacity to adsorb some kinds of aromatic compounds, and it also can perform self-deposit with the adding of electrolytes(NaCl in this case), and complete deposition to the bottom of tubes was accomplished under centrifugation. Elution can then be carried on after the separation of two phases. This work implied that this novel salt-assisted graphene oxide dispersive solid phase microextraction can be applied in adsorbing the aromatic hydrocarbons.(2) Dimethylamine and trimethylamine, which all belong to organic amine compounds, were also selected as the target compounds, we used the same sample pretreatment established before, and combined it with ion chromatography to investigate the adsorption rate of these two kinds of contaminants. This experiment also provided a green, convenient operation and short extraction time. After adding the electrolyte(NaCl in this case), graphene oxide can deposit to the bottom of tubes under centrifugation. Adsorption rate can be estimated by calculating the rest of target compounds existed in the supernatant. Finally, it was found that graphene oxide can adsorb majority of these contaminants under optimized conditions. This work also implied that this novel salt-assisted graphene oxide dispersive solid phase microextraction can be applied in adsorbing the non-aromatic hydrocarbons, here, refered to the organic amine compounds.To sum up, graphene oxide, in our present work, can not only have a good capacity of adsorbing aromatic compounds such as malachite green and crystal violet, but also perform a relatively high adsorption rate to ionic compounds such as organic amine compounds in this work. So, we can tell for sure that salt-assisted graphene oxide dispersive solid phase microextraction will have a broader application in the future.