Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Flow injection spectrophotometric determination of andrographolide from Andrographis paniculata

A simple flow injection colourimetric procedure for determining andrographolide was proposed. It is based on the reaction between andrographolide with 3,5-dinitrobenzoic acid, resulting in an intense purplish red complex with a suitable absorption at 536 nm. A standard or sample solution was injected into the 3,5-dinitrobenzoic acid stream (flow rate of 1.0 ml min⁻¹) which was then merged with potassium hydroxide stream with the same flow rate. Optimum conditions for determining andrographolide were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 5.0-150.0 μg ml⁻¹ and the detection limit was 1.50 μg ml⁻¹ (3σ). The relatives standard deviation of the proposed method calculated from 10 replicate injections of 10.0 and 80.0 μg ml⁻¹ andrographolide were 0.66% and 1.64%, respectively. The sample throughput was 50 h⁻¹. The proposed method has been satisfactorily applied to the determination of andrographolide in herb plant samples.     

Flow injection chemiluminescence determination of paracetamol

A simple chemiluminometric method using flow injection has been developed for the determination of paracetamol (acetaminophen), based on the chemiluminescence produced by the reduction of tris(2,2′-bipyridyl)ruthenium(III). The latter is obtained by oxidation of tris(2,2′-bipyridyl)ruthenium(II) by potassium permanganate in dilute sulphuric acid in the presence of paracetamol. A standard or sample solution was injected into the ruthenium(II) stream (flow rate 1.5 ml min⁻¹) which was then merged with potassium permanganate in dilute sulphuric acid stream (flow rate 0.5 ml min⁻¹). The chemiluminescence intensity is enhanced by the presence of manganese(II) ions. Under the optimum conditions, a linear calibration graph was obtained over the range of 0.3-50.0 μg ml⁻¹ and the detection limit was 0.2 μg ml⁻¹ (s/n = 3). The relative standard deviation of the proposed method calculated from 20 replicate injections of 5.0 μg ml⁻¹ paracetamol was 1.1%. The sample throughput was 90 h⁻¹. The method was successfully applied to the determination of paracetamol in commercial pharmaceutical formulations.     

Optimization of Lactic Acid Production by Pellet-Form Rhizopus oryzae in 3-L Airlift Bioreactor Using Response Surface Methodology

The influence of two key environmental factors, pH and oxygen transfer coefficient (k _La), was evaluated on the lactic acid production as the main answer and, on the size of cell pellets of the fungal strain Rhizopus oryzae KPS106, as second dependant answer by response surface methodology using a central composite design. The results of the analysis of variance and modeling demonstrated that pH and k _La had a significant effect on lactic acid production by this strain. However, no interaction was observed between these two experimental factors. pH and k _La had no significant influence on the pellet size. Optimal pH and k _La of the fermentation medium for lactic acid production from response surface analysis was 5.85 and of 3.6 h^?1, respectively. The predicted and experimental lactic acid maximal values were 75.4 and 72.0 g/l, respectively, with pellets of an average of 2.54?±?0.41 mm. Five repeated batches in series were conducted with a mean lactic acid production of 77.54 g/l. The productivity was increased from 0.75 in the first batch to 0.99 g/l h in the last fifth batch.     

Solid-state dye-sensitized solar cells fabricated by coupling photoelectrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) with silver-paint on cathode

A PEDOT-based dye-sensitized solar cell (DSC) is successfully improved by coupling photoelectrochemically deposited PEDOT layer with an Ag paste-paint on the cathode. With a 9.3 μm thick mesoscopic nanocrystalline TiO(2) film, a maximum cell performance of 3.2% with relatively high V(oc) of around 780 mV is achieved.     

Flow injection spectrophotometric determination of tetracycline in a pharmaceutical preparation by complexation with aluminium(III).

A rapid flow injection (FI) spectrophotometric procedure for tetracycline determination is described. It is based on the injection of a 100 microl sample solution containing tetracycline into merged streams of aluminium(III) chloride (0.01 mol 1(-1)) and Tris-buffer in the presence of KCl (0.06 mol l(-1)), pH 7.0, with the same optimum flow rate of 3.2 ml min(-1). A yellow Al(III)-tetracycline complex was monitored at 376 nm. The flow injection system and the experimental conditions were optimized by means of the univariate method. The procedure was applied to the determination of tetracycline in pharmaceutical preparations with a high sampling rate of at least 165 h(-1). A high precision with a relative standard deviation was obtained less than 0.72 and 0.30% of 5.0 and 10 microg ml(-1) (n=11), respectively. The detection limit (3sigma) and the quantification limit (10sigma) were 0.07 and 0.72 mg l(-1), respectively. There were no interference effects from traditional excipients in the dosage forms when the method was applied to pharmaceutical preparations. The matrix effect could be reduced by the standard addition method.