Fabrication of graphene–ZnO heterostructure-based flexible and thin platform-based UV detector

This work presents the performance evaluation of Graphene/ZnO Schottky junctions grown on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. The fabricated structures include chemical vapour deposition grown graphene layer on ITO-coated PET substrates. Polymethyl methacrylate assisted transfer method has been employed for the successful transfer of graphene from Cu substrate to PET. The smaller D-band intensity (1350 cm−1) compared to G-band (1580 cm−1) indicates good quality of carbon lattice with less number of defects. High-quality ZnO has been deposited through RF sputtering. The deposited ZnO with grain size 50–95 nm exhibited dislocation densities of 1.31270 × 10–3 nm−2 and compressive nature with negative strain of − 1.43156 GPa. Further, the electrical and optical characterization of the devices has been done through device I–V characterization and UV detection analysis. The UV detection capability of the device has been carried out with the aid of a UV-lamp of 365 nm wavelength. The fabricated graphene/ZnO photodetector showed good response to UV illumination. The device performance analysis has been done through a comparison of the device responsivity and detectivity with the existing detectors. The detectivity and responsivity of the fabricated detectors were 7.106 × 109 mHz1/2 W−1 and 0.49 A W−1, respectively.

The Improved Method for Determination of Orotic Acid in Milk by Ultra-Fast Liquid Chromatography with Optimized Photodiode Array Detection

Ultra-fast liquid chromatography (UFLC) with a photodiode array detector (DAD) for simple and rapid determination of orotic acid (OAc) in milk of sheep and cows is described. Milk samples are treated with acetonitrile (1:1, v/v) and then centrifuged at 4 °C. To 1 mL of the obtained supernatant 9 mL of ultrapure water was added. Subsequently, 0.5–6 µL of the resulting solution was injected into the UFLC-DAD system. Separation and quantification of OAc in milk samples was achieved using two Kinetex C18 columns (1.7 µm, 150 mm × 2.1 mm, i.d., 100 Å; Phenomenex) fitted with a pre-column of 4 mm × 2 mm, i.d. (Phenomenex) containing C18 packing material. All separations were performed at a column temperature of 35 °C while the ambient temperature was 21–24 °C. Satisfactory separation of OAc from endogenous species of milk can be achieved using the binary gradient elution program and UV detection at wavelengths 278 nm. Our original procedure resulted in suitable separation and quantification of OAc in milk samples; OAc eluted at 6.44 ± 0.03 min. The total run time of OAc analysis (including re-equilibration) was 27 min. As expected, the OAc peak was absent from the blank when the proposed gradient elution program and UV detection at 278 nm was used. The average recoveries of OAc standards added to milk samples were satisfactory (96.7–105.3%). The low inter-and intra-assay coefficient of variation derived from the measurements of OAc in cow and ovine milk samples (i.e., 0.784%, 1.283% and 0.710%, 1.221%, respectively) and in O-Ac standards (i.e., 0.377% and 0.294%, respectively), as well as high recoveries of OAc added to ovine and cows’ milk (~100%) and the low detection (0.04 ng) and quantification (0.12 ng) limits point to satisfactory accuracy, precision and sensitivity of the reported method. OAc concentrations in ovine milk samples were within the range from 25 to 36 mg/L, while OAc levels in cows’ milk samples was found in the range of 32–36 mg/L. Our original procedure is suitable for routine quantification of OAc in milk of ewes and cows.

QUANTIFICATION OF BILASTINE AND MONTELUKAST COMBINATION IN FORMULATIONS UTILIZING LIQUID CHROMATOGRAPHY: STABILITY STUDIES

Objective: We have developed a “stability-indicating RP-HPLC” procedure for the Bilastine (BLS) and montelukast (MTL) analysis of tablets. Methods: The quantification of BLS and MTL combination was implemented utilising a Waters column (C18, 5 μm, 250 mm and 4.6 mm). Isocratic mobile phase had 60% volume KH2PO4 of 0.1M strength with pH 4.2 units and 40% volume methanol at a flow with 1.0 ml/min speed. UV detection at 232 nm was done to examine BLS and MTL. Stability experiments of BLS and MTL under distinctive environments of stress were also performed. Results: The BLS and MTL were eluted at 1.810 min and 2.551 min, respectively. The responses were found to be linear for the concentration ranges of 10-30 µg/ml (BLS) and 5-15 µg/ml (MTL). Percent comparative standard deviance for precision was 0.331% (BLS) and 0.486% (MTL). Percent assay for accuracy was 98.96% (BLS) and 99.00% (MTL). The detection limit and quantitation limit measures for BLS were 0.018 µg/ml and 0.059 µg/ml, respectively, while for MTL it was 0.024 µg/ml and 0.081 µg/ml, respectively. Robustness studies authorized that the method is robust with percent comparative standard deviance of a highest 1.950%. Conclusion: The developed “stability-indicating RP-HPLC” procedure for the BLS and MTL analysis is simple, sensitive, precise, specific and robust, making it appropriate to the assessment of BLS and MTL in a tablet formulation.