Flow-injection chemiluminescent determination of metoclopramide hydrochloride in pharmaceutical formulations and biological fluids using the [Ru(dipy)(3)(2+)]-permanganate system

A flow-injection (FI) methodology using (2,2′-dipyridyl) ruthenium(II) [Ru(dipy)₃²⁺] chemiluminescence (CL) was developed for the rapid and sensitive determination of metoclopramide hydrochloride. The method is based on the CL reaction of metoclopramide with Ru(dipy)₃²⁺ and KMnO₄ in a sulfuric acid medium. Under the optimum conditions, a calibration graph was obtained over the concentration range 0.005-3.5 μg ml⁻¹ with a limit of detection (S/N=2) of 1 ng ml⁻¹. The correlation coefficient was 0.99993 (n=8) with a relative standard deviation of 0.48% for 10 determinations of 1 μg ml⁻¹ of drug. The method was successfully applied to the determination of metoclopramide in pharmaceutical preparations and biological fluids after IP administration of 25 mg kg⁻¹ dose to rats. The elimination half-life was 2.5±0.4 h.     

Reversed flow injection spectrophotometric determination of chlorate

An interfacing has been developed to connect a spectrophotometer with a personal computer and used as a readout system for development of a simple, rapid and sensitive reversed flow injection (rFI) procedure for chlorate determination. The method is based on the oxidation of indigo carmine by chlorate ions in an acidic solution (dil. HCl) leading to the decrease in absorbance at 610 nm. The decrease in absorbance is directly related to the chlorate concentration present in the sample solutions. Optimum conditions for chlorate were examined. A linear calibration graph over the range of 0.1-0.5 mg L⁻¹ chlorate was established with the regression equation of Y = 104.5X + 1.0, r² = 0.9961 (n = 6). The detection limit (3σ) of 0.03 mg L⁻¹, the limit of quantitation (10σ) of 0.10 mg L⁻¹ and the RSD of 3.2% for 0.3 mg L⁻¹ chlorate (n = 11) together with a sample throughput of 92 h⁻¹ were obtained. The recovery of the added chlorate in spiked water samples was 98.5 ± 3.1%. Major interferences for chlorate determination were found to be BrO₃⁻, ClO₂⁻, ClO⁻ and IO₃⁻ which were overcome by using SO₃²⁻ (as Na₂SO₃) as masking agent. The method has been successfully applied for the determination of chlorate in spiked water samples with the minimum reagent consumption of 14.0 mL h⁻¹. Good agreement between the proposed rFIA and the reference methods was found verified by Student's t-test at 95% confidence level.     

A surface-fluorinated-TiO2-KMnO4 photocatalytic system for determination of chemical oxygen demand

A new method for chemical oxygen demand (COD) determination has been developed, based on photocatalytic oxidative degradation by using a fluorinated-TiO₂-KMnO₄ system. In such a system, a linear correlation is observed between the amount of oxidizable dissolved organic matter and the amount of MnO₄⁻ consumed by the coupled reduction process. Thus, the COD determination is transformed to a simple and direct determination of the deletion of MnO₄⁻. The surface fluorination of TiO₂ nanoparticles can enhance the rate of photocatalytic oxidation of organic matter and the rate of coupled photocatalytic reduction of MnO₄⁻. This makes the method be rapid, environment friendly and easy for operation. Under optimized conditions, this method can respond linearly to COD of potassium hydrogen phthalate (KHP) in the range of 0.1-280 mg L⁻¹, with a detection limit of 0.02 mg L⁻¹ COD. The COD in samples of tap water, lake water and paper industry sewage has been determined satisfactorily by using this method.     

Determination of methimazole and carbimazole by flow-injection with chemiluminescence detection based on the inhibition of the Cu(II)-catalysed luminol-hydrogen peroxide reaction

This paper reports an indirect flow-injection (FI) method for the determination of the anti-hyperthyroid drugs methimazole and carbimazole in pharmaceuticals. The method was based on the inhibition that these thioimidazole drugs caused on the Cu(II)-catalysed chemiluminescence (CL) reaction between luminol and H₂O₂. The CL reaction was induced on-line and injection of the sample produced negative peaks as a result of the Cu(II) complexation by the analytes. The height of the FI peaks was proportional to the drug concentration in the sample. The linear range was 2-100 and 3-120 mg l⁻¹ for methimazole and carbimazole, respectively. The relative standard deviation was 1.9% for methimazole and 2.1% for carbimazole at the 50 mg l⁻¹ level (n=10). Common excipients present in pharmaceutical tablets were found not to interfere with the analysis. The method was applied to the determination of methimazole and carbimazole in pharmaceutical formulations with recoveries in the range 100±4%.     

Determination of iodide by detection of iodine using gas-diffusion flow injection and chemiluminescence

This work describes development of a flow injection (FI) system for determination of iodide, based on the chemiluminescence (CL) reaction between iodine and luminol. Iodide in the sample zone is oxidized to iodine. Employment of a gas-diffusion (GD) unit allows for selective detection of the generated CL (425 nm). Preliminary results showed for concentrations of less than 2 mg L⁻¹, that signals were irreproducible and that the calibration was not linear.In order to solve these problems, a method of ‘membrane conditioning’ was investigated, in which iodide stream was continuously merged with oxidant to generate I₂ that conditioned the GD membrane and tubing. This minimized surface interaction between the active surface and the I₂ generated from the samples, thus improving both precision and sensitivity. By employing membrane conditioning, it has been possible to reliably detect concentrations down to 0.1 mg L⁻¹.At the optimized condition, an excellent linear calibration (r² = 0.999) was obtained from 0.1 to 1.0 mg L⁻¹. The method was successfully applied to determine iodide in some pharmaceutical products such as potassium iodide tablets and a liquid patent medicine. However, for vitamin tablets, ascorbic acid was found to interfere seriously by causing a negative signal.     

Flow injection chemiluminescence determination of naproxen based on KMnO4-Na2SO3 reaction in neutral aqueous medium

A simple, rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of naproxen. It was found that strong CL signal was generated when naproxen was mixed with KMnO₄ and Na₂SO₃ in neutral aqueous medium. Under the optimum experimental conditions, the CL intensity was linearly related to the concentration of naproxen from 4.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g mL⁻¹ (r = 0.9993). The detection limit was 2 × 10⁻⁹ g mL⁻¹ naproxen, the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ naproxen solution was 1.5% (n = 11) and the sampling frequency was 120 h⁻¹. The method was applied to the determination of naproxen in pharmaceutical preparation with satisfactory results. The mechanism of CL reaction was discussed briefly.     

Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus.Calibration was found to be linear up to 20 mg P L⁻¹, with a detection limit (3s_b/S) of 0.08 mg P L⁻¹, an injection throughput of 75 injections h⁻¹ and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L⁻¹, with a detection limit (3s_b/S) of 0.5 mg P L⁻¹, an injection throughput of 11 injections h⁻¹ and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.     

High throughput method for the analysis of cetrizine hydrochloride in pharmaceutical formulations and in biological fluids using a tris(2,2'-bipyridyl)ruthenium(II)-peroxydisulphate chemiluminescence system in a two-chip device

A fast, economic and sensitive chemiluminescence (CL) method has been developed for the analysis of cetrizine hydrochloride (CET) in pharmaceutical formulations and in biological fluids. The CL method is based on the oxidation of tris(2,2′-bipyridyl)ruthenium(II) (Ru (bipy)₃²⁺) by peroxydisulphate in a two-chip device. Up to 180 samples can be analysed per hour, consuming only minute quantities of reagents. Three instrumental setups were tested to find the most economical, sensitive and high throughput setup. In the first setup, a continuous flow of sample and CL reagents was used, whereas in the second setup, a fixed volume (2 μL) of (Ru (bipy)₃²⁺) was introduced into a continuous infusion of peroxydisulphate and the sample. In the third design, a fixed volume of sample (2 μL) was injected while the CL reagents were continuously infused. Compared to the first setup, a 200% signal enhancement was observed in the third setup. Various parameters that influence the CL signal intensity, including pH, flow rates and reagent concentrations, were optimized. A linear response was observed over the range of 50 μg L⁻¹ to 6400 μg L⁻¹ (R² = 0.9959) with RSD values of 1.1% (n = 15) for 1000 μg L⁻¹. The detection limit was found to be 15 μg L⁻¹ (S/N = 3). The amount of consumed sample was only 2 μL, from which the detected amount of CET was found to be 6.5 × 10⁻¹⁴ mol. This procedure was successfully applied to the analysis of CET in pharmaceutical formulations and biological fluids.     

Chemiluminescence determination of carbofuran at trace levels in lettuce and waters by flow-injection analysis

A simple, fast chemiluminescence (CL) flow-injection (FI) method based on the reaction of luminol with KMnO₄ in alkaline medium has been described for the direct determination of carbofuran. The method is based on the enhancing effect in the emission light from the oxidation of luminol produced in presence of carbofuran. The optimisation of instrumental and chemical variables influencing the CL response of the method has been carried out by applying experimental design, using the proposed flow-injection manifold. Under the optimal conditions, the CL intensity was linear for a carbofuran concentration over the range of 0.06-0.5 μg ml⁻¹, with a detection limit of 0.02 μg ml⁻¹. The method has been successfully applied to the determination of carbofuran residues in spiked water and lettuce samples.     

A chemiluminescence biochemical oxygen demand measuring method

A new chemiluminescence biochemical oxygen demand (BOD_CL) determining method was studied by employing redox reaction between quinone and Baker's yeast. The measurement was carried out by utilizing luminol chemiluminescence (CL) reaction catalyzed by ferricyanide with oxidized quinone of menadione, and Saccharomyces cerevisiae using a batch-type luminometer. In this study, dimethyl sulfoxide was used as a solvent for menadione. After optimization of the measuring conditions, the CL response to hydrogen peroxide in the incubation mixture had a linear response between 0.1 and 100 μM H₂O₂ (r² = 0.9999, 8 points, n = 3, average of relative standard deviation; R.S.D._av = 4.22%). Next, a practical relationship between the BOD_CL response and the glucose glutamic acid concentration was obtained over a range of 11-220 mg O₂ L⁻¹ (6 points, n = 3, R.S.D._av 3.71%) with a detection limit of 5.5 mg O₂ L⁻¹ when using a reaction mixture and incubating for only 5 min. Subsequently, the characterization of this method was studied. First, the BOD_CL responses to 16 pure organic substances were examined. Second, the influences of chloride ions, artificial seawater, and heavy metal ions on the BOD_CL response were investigated. Real sample measurements using river water were performed. Finally, BOD_CL responses were obtained for at least 8 days when the S. cerevisiae suspension was stored at 4 °C (response reduction, 69.9%; R.S.D. for 5 testing days, 18.7%). BOD_CL responses after 8 days and 24 days were decreased to 69.9% and 35.8%, respectively, from their original values (R.S.D. for 8 days involving 5 testing days, 18.7%).     

Determination of N-methylcarbamate pesticides in water and vegetable samples by HPLC with post-column chemiluminescence detection using the luminol reaction

In this paper we proposed a reverse high performance liquid chromatography method for the simultaneous determination of three N-methylcarbamates (NMCs) named carbofuran, carbaryl and methiocarb, using the post-column chemiluminescence (CL) detection with the luminol reaction. This method is based on the enhancing effect of these analytes on the CL emission generated by the oxidation of luminol with potassium permanganate in alkaline medium. The separation was reached in less than 14 min using a C18 column and an isocratic binary mobile phase consisting of acetonitrile:water (50:50, v/v) pumped at a flow rate of 1 mL min⁻¹. CL reagents (luminol and KMnO₄) were incorporated by means of a peristaltic pump and were firstly mixed using a three-way connector. Then this stream was mixed with the eluate using another three-way connector just before reaching the detection cell. The optimization of variables affecting the CL reaction (reaction medium, concentration, flow rate of reagents and distance between both connectors) were optimized by means of experimental designs. Ethiofencarb, a NMC which has nowadays fallen into disuse was used as internal standard. For the analysis of theses pesticides in real water samples a pre-treatment step consisting of solid phase extraction (SPE) was conducted in order to reach sensitivity levels below the legal maximum concentration permitted. In the case of vegetable sample, SPE was used for matrix cleaning purpose.     

The development of sequential injection analysis coupled with lab-on-valve for copper determination

A sequential injection analysis (SIA) using lab-on-valve with air segmentation and spectrophotometric detection was designed for copper(II) determination. It is based on the reaction of copper(II) and 2-carboxy-2′-hydroxy-5′-sulfoformazyl benzene (Zincon) in a weak alkaline solution between the air zones. Beer's Law was obeyed over the range of 0.1-2.0 mg L⁻¹ copper(II) with a correlation coefficient 0.9985 and a slope of 0.2893 absorbance unit/mg L⁻¹. The relative standard deviation was 2.0% for a series of 10 measurements of 0.5 mg L⁻¹ copper(II) solution. The detection limit (3 S/N) and the limit of quantification (LOQ) were 0.05 and 0.17 mg L⁻¹ respectively. This method has been successfully applied to determination of copper(II) in wastewater with a sample throughput of 120 h⁻¹. The method is superior to the batchwise method in that it provides fully automation, rapidity, less reagents and sample consumption with little waste generation.     

Determination of orthophosphates using a macro segmented flow analyzer (MSFA) based on colorimetric detection

Fabrication of a macro segmented flow analysis (MSFA) system based on reconfiguration of the manifold by adjustment of the sample/reagent ratio, has been found to produce a sensitive method for orthophosphate analysis based on colorimetric detection at 880 nm. Optimization of sample tube length, reaction temperature and molybdate concentration in the carrier solutions has been carried out. The larger sample tube internal diameter led to the combined advantages of better sensitivities, wider working range and higher sample throughput over most existing methods. Using the optimized conditions of 50.0 cm sample tube length (1.6 mm i.d.), 37.0 °C reaction temperature and 0.0113 M molybdate concentration in the carrier solution, the calibration model for orthophosphate standard solutions was found to be linear (y = 0.04895x + 0.003561; correlation coefficient, r²=0.9970) over the working range 0.01-2.00 mg l⁻¹ orthophosphate. The volume of the sample injected was 1.396 ml at a flow rate of 6.0 ml min⁻¹. The sample throughput of this MSFA method was 40 samples per an hour, with a detection limit of 4.0 μg l⁻¹, and %R.S.D.’s below 5%. The MSFA method was successfully applied to analysis of water and wastewater samples.     

Flow injection conductometric system with gas diffusion separation for the determination of Kjeldahl nitrogen in milk and chicken meat

A simple flow injection (FI) conductometric system with gas diffusion separation was developed for the determination of Kjeldahl nitrogen (or proteins) in milk and chicken meat. The sample was digested according to the Kjeldahl standard method and the digest was diluted and directly injected into the donor stream consisting of 4 M NaOH. In alkaline medium, ammonium was converted to ammonia, which diffused through the PTFE membrane to dissolve in an acceptor stream (water). Dissociation of ammonia caused a change in conductance of the acceptor solution, which was linearly proportional to the concentration of ammonium originally present in the injected solution. A conductometric flow through cell and an amplifier circuit was fabricated, which helped improve sensitivity of the conductometric detection system. With using a plumbing Teflon tape as a gas diffusion membrane and without thermostating control of the system, a linear calibration graph in range of 10-100 mg L⁻¹ N-NH₄ was obtained, with detection limit of 1 mg L⁻¹ and good precision (relative standard deviation of 0.3% for 11 replicate injections of 50 mg L⁻¹ N-NH₄). The developed method was validated by the standard Kjeldahl distillation/titration method for the analysis of milk and chicken meat samples. The proposed system had sample throughput of 35 h⁻¹ and consumed much smaller amounts of chemical than the standard method (275 mg vs 17.5 g of NaOH per analysis, respectively).     

Preparation of photocatalytic nano-ZnO/TiO2 film and application for determination of chemical oxygen demand

A composite nano-ZnO/TiO₂ film as photocatalyst was fabricated with vacuum vaporized and sol-gel methods. The nano-ZnO/TiO₂ film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO₂ and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO₂ film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO₂ film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO₂ film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1 mg l⁻¹, COD values with the linear range of 0.3-10.0 mg l⁻¹ were achieved. The results were in good agreement with those from the conventional COD methods.     

Hybrid sequential injection-flow injection manifold for the spectrophotometric determination of total sulfite in wines using o-phthalaldehyde and gas-diffusion

A new automated spectrophotometric method for the determination of total sulfite in white and red wines is reported. The assay is based on the reaction of o-phthalaldehyde (OPA) and ammonium chloride with the analyte in basic medium under SI conditions. Upon on-line alkalization with NaOH, a blue product is formed having an absorption maximum at 630 nm. The parameters affecting the reaction - temperature, pH, ionic strength, amount concentration and volume of OPA, amount concentration of ammonium chloride, flow rate and reaction coil length - and the gas-diffusion process - sample and HCl volumes, length of mixing coil, donor flow rate - were studied. The proposed method was validated in terms of linearity (1-40 mg L⁻¹, r = 0.9997), limit of detection (c_L = 0.3 mg L⁻¹) and quantitation (c_Q = 1.0 mg L⁻¹), precision (s_r = 2.2% at 20 mg L⁻¹ sulfite, n = 12) and selectivity. The applicability of the analytical procedure was evaluated by analyzing white and red wine samples, while the accuracy as expressed by recovery experiments ranged between 96% and 106%.     

Investigation on the application of titania nanorod arrays to the determination of chemical oxygen demand

In the present paper, the TiO₂ nanorod arrays electrode was developed as a sensor for the determination of chemical oxygen demand (COD) based on a photoelectrochemical degradation principle. Effects of common parameters, such as applied potential, light intensity and pH on its analytical performance were investigated. Under the optimized conditions, the nanorod arrays electrode was successfully applied in the COD determination for both synthetic and real samples. In the COD determination, the proposed method can achieve a practical detection limit of 18.3 mg L⁻¹ and a linear range of 20–280 mg L⁻¹. Furthermore, the results obtained by the proposed method were well correlated with those obtained using the conventional (i.e., dichromate) COD determination method. The main advantages of this COD determination method were its simplicity, long term stability and environmental friendly (corrosive and toxic reagents not consumed). This work would open a new application area (COD determination) of the TiO₂ nanorod arrays.     

A simple miniaturised photometrical method for rapid determination of nitrate and nitrite in freshwater

A rapid, simple miniaturised photometrical method was developed for the determination of nitrate and/or nitrite in freshwater samples. All procedures, including sample buffering, reduction by copperised cadmium granules, colour development and absorbance determination, were completed in a 96-well microplate. The factors governing the nitrate reduction and its recovery were investigated in detail, and the optimised analysing conditions were established. Nitrate was quantitatively reduced by copperised cadmium granules with a high reduction efficiency (96.59 ± 0.96%). The proposed method gave a linear calibration ranging from 0.01 to 1.50 mg L⁻¹ for NO₂⁻-N and 0.02 to 1.50 mg L⁻¹ for NO₃⁻-N. The detection limits for nitrite and nitrate were 2 and 4 μg L⁻¹, respectively. The proposed method allowed at least 48 samples to be simultaneously analysed in duplicate, with good precision, within 90 min for nitrate and 30 min for nitrite, and was successfully applied to actual freshwater sample analysis with a recovery of 98.02 ± 1.04% for nitrite and 99.72 ± 1.39% for nitrate. This method produced accurate results comparable to standard methods, provided a much higher sample throughput than conventional methods and could be routinely used in actual freshwater sample monitoring.     

Simple sequential injection analysis system for rapid determination of microalbuminuria

A simple, specific and sensitive sequential injection analysis (SIA) system based on non-immunoassay fluorescent detection has been developed for the determination of urinary albumin. The specific binding of the dye Albumin Blue 580 (AB 580) to albumin in urine generated high emission fluorescent signals. The excitation and emission wavelengths were set at 590 and 610 nm, respectively. The analytical range was obtained from 1 to 100 mg L⁻¹, with a detection limit of 0.3 mg L⁻¹ (S/N = 3). The SIA system gave high precision with relative standard deviations (R.S.D.s) of 0.9% and 1.4% when evaluated with 15 and 100 mg L⁻¹ albumin (n = 15), respectively. The method exhibited good reproducibility, as assessed by performing four analytical curves on different days, and intra-run CVs (2.3-3.3%) and inter-run CVs (3.8%) were obtained. Rapid operation was achieved with a sample throughput of 37 h⁻¹. This method was successfully applied to the determination of urinary albumin, and the method was highly correlated with the immunoturbidimetric method (r² = 0.965; n = 72).