Vanadium preconcentration using magnetic solid phase extraction method and determmination by ICP-OES

Analyte preconcentration is required before starting the determination of trace elements. The reason for this is that trace elements are found in different matrix environments and their concentrations are very low in natural samples. With the enrichment methods used in trace analysis, the following facilities are provided in the determination step: By increasing the trace element concentration, the determination capacity of the method is increased. Since trace elements are taken to the appropriate environment, interference from the environment is eliminated. This increases the sensitivity of the method. Since large sample quantities can be worked with, errors due to sample inhomogeneity are avoided. It becomes easy to simulate the sample matrix with standards. Because with separation, trace elements are taken into the known matrix. As a result, accuracy increases. As the disrupting matrix is replaced with the appropriate matrix, ground interferences are reduced. Selectivity increases. Many enrichment methods are used in trace element analysis. Solid phase extraction, liquid-liquid extraction, co-precipitation, cloud point extraction, ion exchange, electrolytic deposition and evaporation are some of these methods. In the present study, the adsorption process was carried out using the magnetic solid phase extraction method, one of the extraction methods. The reason for choosing this study's solid phase extraction method is its benefits. Thanks to this method, organic solvents are used less, waste generation is less, and the solid phase can be used repeatedly, reducing the matrix effect and providing a higher enrichment factor. The reasons for choosing magnetic nanoparticles as adsorbents are that they have a large surface area because they are nano-sized, and they interact easily with the target analyte. They provide high selectivity as their surfaces are modified as desired. In addition, magnetic nanoparticles can be easily separated in the solution environment since they can easily interact with the externally applied magnetic field, and centrifugation processes are not required. When magnetic nanoparticles are found in the bare state, they form aggregation, reducing their surface area, and this minimizes the adsorption capacity. This clumping formed by the coating process is prevented. Synthesis of Fe3O4 nanoparticles coated with surfactant Igepal Co-520 as adsorbent for magnetic solid phase extraction was carried out. The presented studies describe the synthesis of Fe3O4 nanoparticles coated with different ligands for magnetic solid phase extraction as adsorbents. Nanoparticles synthesized for heavy metal determination were characterized by FESEM, EDX, XRD, FT-IR, and TGA and determined by ICP-OES. Optimum conditions for speciation and enrichment were found by adjusting pH value, adsorbent amount, and contact time. Also, adsorption isotherms and kinetics, foreign ion studies, and analytical values were carried out. Magnetic nanoparticles (MNP) carrying the target metals are easily separated from the aqueous solution by applying an external magnetic field; therefore, filtration or centrifugation was not required. Both methods are compatible with Freundlich and Langmuir's isotherm models. Samples that carried target metals were analyzed to find the method's accuracy, and relative recoveries were found between 95 and 105%. Indium solution was used as an internal standard in all experiments. In the study, Fe3O4 nanoparticles were coated with Igepal Co-520 and used in vanadıum speciation. In the study, optimum conditions were found to be pH=3, the adsorbent amount was 5 mg magnetic nanoparticle, and the contact time was 120 minutes. Recovery of V5+ from aqueous solution was carried out under these optimum conditions. In isotherm studies, the effect of V5+ concentration on adsorption was investigated by changing values between 1 mg/L and 100 mg/L. Langmuir model (R2>0.99) seems to be more suitable for V5+ adsorption than the Freundlich model (R2<0.87). The Langmuir isotherm model explains that the adsorption takes place in a single layer compared to the Freundlich isotherm model. According to this, it can be said that the adsorption in the study is single-layered. Adsorption kinetic models were evaluated by working with pseudo-first-order and pseudo-second-order equations. It was seen that the pseudo-quadratic equation (R2>0.89) was fitter for modeling than the pseudo-first-order equation (R2<0.56). The enrichment factor (EF), the limit of detection (LOD), and relative standard deviation (RSD), determination limit (LOQ) was calculated as 114, 278 µg/L, 83 µg/L and 1,20%, respectively. The effects of acidic (HCl) and basic (NaOH) media on the desorption of V5+ ions adsorbed on the magnetic Fe3O4 surface were investigated and compared at different molars. Accordingly, since the maximum recovery was achieved when HCl was at a concentration of 1 mol/L, the HCl concentration was used as 1 mol/L in further studies. In the case of NaOH as a desorption agent, a maximum recovery of 87.18% was achieved, but 100% recovery was not achieved. Since the electrostatic attraction between magnetic Fe3O4 and V5+ decreases as the HCl concentration increases, it is understood that the analyte can be easily separated from the adsorbent surface.