In this study, the nitrogen diffusion in different microstructures of CK45 steel was studied. Different microstructures were achieved by different heat treatment cycles as annealing, normalising and quench tempering. After heat treatment, plasma nitriding was performed at 550°C temperature, nitriding times of 5 h, in a gas mixture containing 25 vol.-H2/75 vol.-N2 and DC pulsed plasma nitriding unit. The surface, cross-section and the thickness of diffusion and white layers of specimens were studied in terms of optical and scanning electron microscopy. Surface phases have been studied by X-ray diffraction analysis. Results showed that by normalising the samples, higher diffusion depths could be achieved and the white layer thickness would be also higher. Other results showed that core hardness of quench tempered specimens could decrease after plasma nitriding due to being subjected to nitriding process temperature.
A graphene oxide‐based aerogel was synthesized and applied to the extraction and the determinations with the high‐performance liquid chromatography‐ultraviolet detector. After the characterization of the produced graphene‐aerogel, it was utilized as a dispersive solid‐phase extraction sorbent for risperidone extraction from plasma samples. Aerogels are materials with a large surface area‐to‐mass ratio and plenty of core with functional groups which can easily attach to the analytes to extract them to the second phase. The suggested method determined risperidone in plasma samples in the wide dynamic range from 20 ng/ml to 3 μg/ml. The limits of detection and quantification of the developed method were calculated as 2.4 and 8.2 ng/ml, respectively. As a novel feature, the developed method has no need to precipitate plasma proteins, improving the analytical performance of the analysis. Also, for the first time, the produced materials were utilized for the extraction of risperidone from the plasma samples. The obtained results revealed that the developed approach could be employed as an accurate method for the quantification of risperidone in real plasma samples.
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