Search Results
You are looking at 11 - 13 of 13 items for
- Author or Editor: M. Ramadan x
- Refine by Access: All Content x
Two sensitive, specific, and selective stability-indicating chromatographic methods were developed for the determination of cyclobenzaprine HCl (CZ) and asenapine maleate (AS) in pure forms, in the presence of their degradation products and in their pharmaceutical formulations. The first method was an isocratic reversed-phase high-performance liquid chromatography (RP-HPLC). Analysis was performed on cyano column using a mobile phase consisting of acetonitrile–(0.05 m) potassium dihydrogen phosphate buffer (pH 3 ± 0.1) (70:30, v/v) with a flow rate of 1.5 mL min−1 and ultraviolet (UV) detection at 290 nm for the determination of CZ, and methanol–(0.05 m) potassium dihydrogen phosphate buffer (pH 6 ± 0.1) (70:30, v/v) with a flow rate of 1.5 mL min−1 and UV detection at 220 nm for the determination of AS. The second method was thin-layer chromatography (TLC), using silica gel 60 F254 plates and toluene–methanol–chloroform-ammonia solution 33% (5:3:6:0.1, by volume) as the mobile phase for the two drugs. The spots were scanned densitometrically at 290 and 220 nm for the determination of CZ and AS, respectively. The methods were validated according to the International Conference on Harmonization (ICH) guidelines, and the acceptance criteria for linearity, accuracy, precision, specificity, and system suitability were met in all cases. The linearity ranges were 2.5–25 μg mL−1 for the RP-HPLC method and 5–50 μg band−1 for the TLC method for both drugs. The limits of detection for the RP-HPLC method were 0.250 and 0.578 for CZ and AS, respectively, while the limits of quantification were 0.758 and 1.572 for CZ and AS, respectively. The limits of detection for the TLC method were 1.355 and 1.284 for CZ and AS, respectively, while the limits of quantification were 4.472 and 3.891 for CZ and AS, respectively. The results were compared statistically at a 95% confidence level with the reported methods. There were no significant differences between the mean percentage recoveries and the precisions of the two methods.
Abstract
Monitoring benzoylphenylureas (BPUs) residues in ready-to-eat vegetables is of great interest for an adequate assessment of human pesticide exposure. A rapid, inexpensive, simple, and effective method for determining 8 BPUs insecticides in tomatoes and cucumbers was developed and validated. Vortex-assisted liquid-liquid extraction (VA-LLE) followed by dispersive solid-phase extraction (d-SPE) using graphitized carbon black (GCB) for cleanup was used before LC-MS/MS analysis. Different parameters were optimized, including the type and volume of extractants, vortex time, and the type and amount of adsorbents used for cleanup. The evaluation showed that the method has excellent linearity (R 2 ≥ 0.994). The recovered 8 BPUs insecticides from spiked tomato and cucumber samples at 0.01, 0.05, and 0.25 mg kg−1 ranged from 83.2 to 105.2%, with RSD of 4.9–14.6%. The limits of quantitation (LOQs) were 0.0025 mg kg−1 (0.005 mg kg−1 for lufenuron). Within-day repeatability ranged from 3.9 to 13.9%, while between-day repeatability ranged from 8.9% to 17.7%. The optimized method was used to analyze 100 samples of tomatoes and cucumbers marketed in Saudi Arabia.
Abstract
A computational model is developed to investigate the convective heat transfer properties and the fluid flow characteristics of cupric oxide - water nano-fluid in a horizontal circular pipe aiming to provide insights into optimizing heat transfer in such systems. A twisted tape with varied twist ratios is inserted. This quantitative investigation used five Reynolds number from 4,000 to 12,000 under a uniform heat flux scenario of 25,000 W m−2. All experiments were performed as a single-phase fluid with cupric oxide values of 0, 0.4, 1, and 2% by volume. By reducing the twist ratio and increasing volume concentration, the average heat transfer coefficient of cupric oxide-water nano-fluid was improved. For a twist ratio of 4D, the maximum heat transfer improvement was 228% greater than the plain pipe. The presence of twisted tape with modest step ratios causes the friction factor to grow.
