Development of graphene oxide-based liquid chromatography (HPLC) stationary phases and their use in the analysis of pharmaceutical molecules

In this thesis, it is aimed to obtain graphene oxide and reduced graphene oxide, which have applications in many fields such as medicine, pharmacy, chemistry, electrical-electronics, food, sensors, as HPLC stationary phase, characterization, determination of method parameters for the separation of paracetamol and caffeine, which are active ingredients of drugs, and validation of the developed methods. Graphene oxide to be used as stationary phase was synthesized by modified hummers method, immobilized on aminopropylsilica and the obtained graphene oxide silicon (GO-Si) was reduced with hydrazine. The obtained graphene oxide, GO-Si and reduced graphene oxide silicon (rGO-Si) were characterized by UV-vis, FTIR, XRD, TEM and SEM analyses. At the end of FTIR analyses, it was found that graphene oxide has a high amount of -OH, -COOH and C-O-C functional groups, GO-Si is connected by amide bonding and partially reduced oxygen groups on rGO-Si. XRD, TEM and SEM analyses supported the FTIR analysis. Chromatographic separations for paracetamol and caffeine were carried out under isocritical and gradient conditions on GO-Si and rGO-Si stationary phases filled into empty columns under high pressure. At the end of the studies, the best separation for paracetamol and caffeine in GO-Si stationary phase was determined in Method 9 developed under gradient conditions. The validation parameters of the developed Method 9 were calculated as maximum relative standard deviation 0.54, recovery values in the range of 98%-99%, LOD and LOQ values 6x10-3 - 6.5x10-3 mg/L and 2x10-2 - 2.2x10-2 mg/L for paracetamol and caffeine, respectively. A t-test was performed for the developed method and its usability was proven. For rGO-Si stationary phase, 21 different methods were developed by chemometric design and the most suitable method was determined. Suitable method conditions were determined as mobile phase composition 81.3% methanol 18.7% acetonitrile, flow rate 1.2 mL/min and temperature 23°C. The validation parameters of the developed method were calculated as maximum relative standard deviation 0.85, recovery values in the range of 90%-85%, LOD and LOQ values of 4,5x10-3 - 7,7x10-3 mg/L and 1,5x10-2 - 2,6x10-2 mg/L for paracetamol and caffeine, respectively. A t-test was performed for the developed method and its usability was proved.