A magnetic solid-phase extraction (MSPE) method was developed for the facile and sensitive determination of sulfadiazine prior to high-performance liquid chromatography (HPLC) analysis. The magnetic sorbent was prepared by the chemical co-precipitation of Fe₃O₄ magnetic nanocomposites modified with biochar. Characterization of the synthesized Fe₃O₄@BC-PN (Fe₃O₄ loaded pine leaves derived biochar) was performed by scanning electron microscopy – energy dispersive x-ray spectrometry (SEM-EDS), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and Brunauer – Emmett – Teller (BET) surface analysis. The saturation magnetization value was 17.95 emu/g by vibrating sample magnetometry. The Fe₃O₄@BC-PN particle sizes were determined to be 11.8 nm using the Debye-Scherrer relationship. The pH, mass of adsorbent, type, and volume of eluent were optimized. The limits of detection and quantification of the developed MSPE HPLC method were 10.7 μg/L and 35.5 μg/L, respectively. The intra-day and inter-day repeatabilities were below 4.2% and 7.7%, respectively. The developed method was employed to determine trace levels of sulfadiazine in spiked water samples.

Magnetic biochar (Fe₃O₄-BCPP) was prepared by using iron oxide nanoparticles, and biochar which is obtained from pomegranate peel. The Fe₃O₄-BCPP were characterized by Brunauer-Emmett-Teller analysis, X-ray diffraction analysis, scanning electron microscopy, and vibrating sample magnetometer. The adsorption properties of Fe₃O₄-BCPP for sulfadiazine in water were investigated. The Fe₃O₄-BCPP had good adsorption properties and separated well from aqueous solution by a permanent magnet due to superparamagnetic property and magnetic saturation value. Therefore, Fe₃O₄-BCPP has potential application for the removal of sulfadiazine from water samples.

Objectives: To describe a method for the determination of urea in blood serum using urease enzyme and 3-MPA-capped CdTe quantum dots. Materials and Methods: The method is based on the increase in pH of the solution as a result of the reaction between urea and urease, which causes an increase in the phosphorescence signal of MPA-CdTe quantum dots in the pH range of 2.5-5.0. Under the optimum conditions, the linear range of urea was 0.016-0.16 mM (1-10 mg/L) and the limit of detection based on 3 s/b was calculated as 0.003 mM (0.17 mg/L). The relative standard deviation was calculated as 3.4% at 4 mg/L urea concentration (n=7). Results: The method was applied to human serum samples. The same samples were analyzed by an independent laboratory and the results were not statistically different, at 95% confidence level (F test). Conclusion: The proposed method does not need sample pretreatment, is simple, selective, and cost-effective for the determination of urea in serum samples.