A kinetic investigation of removal of chromium from aqueous solutions with a strong cation exchange resin

A kinetic investigation was performed with an ion exchange resin for chromium. A strong cation exchange resin (Amberlite IR 120) was used for removal of chromium. The effects of concentration, resin amount, and stirring speed on kinetics were investigated. The metal concentration range studied was between 5 to 160 mg/dm³ (the amount of solution was 4 dm³), the resin amount range was between 5 to 20 mg, and the stirring speed range was between 1000 to 3500 rpm. Equilibrium experiments were performed for calculation of separation factor. Kinetic studies were done using a Kressman-Kitchener stirrer reactor system and the results were compared with existing kinetic models. Two models, Nernst-Plank film diffusion control model (fdc) and solid phase diffusion control model (pdc), respectively were identified, and the dependence of the rate on parameters such as solution concentration, resin amount, stirring speed, etc. was examined for each of them. The interpretation of these data shows that the system is probably controlled by both film and particle diffusion.     

An electrochemical sensor based on molecularly imprinted polydopamine coated on reduced graphene oxide for selective detection of ornidazole

The electrochemical sensing of ornidazole (OR) was achieved with a highly selective sensor fabricated by a combination of an electrochemically reduced graphene oxide (ERGO) and molecularly imprinted polydopamine (PDA). The sensor (OR-imp@PDA/ERGO/GCE) was synthesized by electrochemical polymerization of dopamine (DA) on ERGO modified glassy carbon electrode (GCE). The analytical response of the sensor changed linearly with OR concentration varying from 1.5 × 10⁻⁹ M to 1.0 × 10⁻⁸ M and 1.0 × 10⁻⁸ M to 2.0 × 10⁻⁷ M, and the detection limit was defined as 1.1 × 10⁻⁹ M. The proposed sensor ensured the highly sensitive detection of OR concentration because of the advantages of ERGO and molecularly imprinted PDA.     

Determination of bupropion using liquid chromatography with fluorescence detection in pharmaceutical preparations, human plasma and human urine

A novel pre-column derivatization reversed-phase high-performance liquid chromatography with fluorescence detection is described for the determination of bupropion in pharmaceutical preparation, human plasma and human urine using mexiletine as internal standard. The proposed method is based on the reaction of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with bupropion to produce a fluorescent derivative. The derivative formed is monitored on a C18 (150 mm × 4.6 mm i.d., 5 μm) column using a mobile phase consisting of methanol-water 75:25 (v/v), at a flow-rate of 1.2 mL/min and detected fluorimetrically at λ(ex) = 458 and λ(em) = 533 nm. The assay was linear over the concentration ranges of 5-500 and 10-500 ng/mL for plasma and urine, respectively. The limits of detection and quantification were calculated to be 0.24 and 0.72 ng/mL for plasma and urine, respectively (inter-day results). The recoveries obtained for plasma and urine were 97.12% ± 0.45 and 96.00% ± 0.45, respectively. The method presents good performance in terms of precision, accuracy, specificity, linearity, detection and quantification limits and robustness. The proposed method is applied to determine bupropion in commercially available tablets. The results were compared with an ultraviolet spectrophotometry method using t- and F-tests.     

Determination and validation of duloxetine hydrochloride in capsules by HPLC with pre-column derivatization and fluorescence detection

A high-performance liquid chromatographic (HPLC) method is described for the determination of duloxetine hydrochloride in capsules. The method was based on pre-column derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole using the fluorimetric detection technique. Duloxetine hydrochloride was analyzed by HPLC using an Inertsil C18 column (5 μm, 150 × 4.6 mm) and mobile phase consisted of methanol and water (65:35, v/v). The fluorescence detector was adjusted at excitation and emission wavelengths of 461 and 521 nm, respectively. The linearity of the method was in the range of 10-600 ng/mL. Limits of detection and quantification were 0.51 and 1.53 ng/mL, respectively. The proposed method was successfully applied for determination of duloxetine hydrochloride in its pharmaceutical preparation. The results were in good agreement with those obtained using a reference method.