Fabrication Of Graphene Oxide@SiO₂ As Stationary Phase And Its Application For The Determination Of Melamine In Food Samples

Objectives Graphene oxide?GO?, as a two-dimensional nanomaterial, has attracted tremendous attention for its unique structure and excellent adsorption performance.Graphene oxide?GO? materials have been developed as chromatographic stationary phase for the separation of neutral and non-polar compounds in reversed phase chromatography. In this study, GO bonded silica?GO@Si O₂? composites were prepared and used as stationary phase for the separation of polar compound melamine in milk and egg samples.Methods GO was covalently bonded to the aminosilica microspheres using N,N'-dicyclohexylcarbodiimide?DCC? as coupling agent to form GO@Si O₂ composites by coupling the amino groups of aminosilica and the carboxyl groups of GO. The effects of the amount of GO?7.5-150 mg? and the coating times?1-2 times? on the performance of stationary phase were evaluated using melamine as model analyte. The prepared GO@Si O₂ was characterized by scanning electron microscope?SEM? and Raman spectroscopy. GO@Si O₂ composites were developed as stationary phase and the chromatographic properties of bare Si O₂ and GO@Si O₂ were investigated by a series of polar compounds, such as melamine, dicyandiamide, clenbuterol, cyanuric acid, and acetylsalicylic acid. The prepared GO@Si O₂ column was used as analytical column for the determination of melamine in egg and milk samples. The chromatographic conditions were optimized including the types of mobile phase?ACN-H2 O, ACN-0.1%FA, ACN-10mmol/L NH4 OAC and ACN-10 mmol/L NH4OAC-0.1%FA?, the concentration of NH4OAC?0-50 mmol/L?, and the ratios of ACN and 10 mmol/L NH4OAC?90:10, 80:20,70:30, 60:40, 50:50, V/V?. Under optimum conditions, the proposed method was evaluated in terms of linearity, precision, repeatability, limits of detection?LODs?, limits of quantification?LOQs?, and recovery.Results The SEM images indicated that the surface of spherical aminosilica composites was tightly covered by the highly wrinkled GO nanosheets, and the Raman spectra revealed that GO@Si O₂ had obvious characteristic peaks at 1380 and 1580 cm-1. It could be concluded that GO was successfully bonded to the surface of the aminosilica composites. GO@Si O₂ composites were developed as stationary phase and thechromatographic properties of bare Si O₂ and GO@Si O₂ were investigated. Compared with bare Si O₂ stationary phase, the retention factor of amino analytes such as melamine and dicyandiamide was improved significantly. Therefore, the GO@Si O₂ column was used as analytical column for the determination of melamine in egg and milk samples using the mixture of ACN-10 mmol/L NH4OAC?80:20, V/V? as the mobile phase. The proposed method was linear over the range of 0.2-50.0 ?g/m L with a linear regression coefficient of 0.9999. The limit of detection of melamine was 0.25 ?g/kg, and the limit of quantification for melamine was 0.87 ?g/kg. The average recoveries ranged from 84.7%-93.9% at the three spiked levels of 1.0, 2.0 and 10.0 ?g/kg with the relative standard deviations?RSDs? between 4.1%-6.3%.Conclusions The GO@Si O₂ stationary phase was synthesized and the chromatographic behavior of the polar compounds on the column was investigated. The GO@Si O₂ stationary phase gave a better separation for polar amino analytes in hydrophilic mode and The proposed method could be sucessfully used for the analysis of melamine in milk and eggs and extended the futher application of GO stationary phase. GO@Si O₂ chromatographic column was a powful alternative for commercial HILIC columns due to the advantageous of low cost and good chromatographic performance.