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 kinetic spectrophotometric method for the determination of trace amounts of nitrite

In this work, a new, simple and sensitive flow injection catalytic kinetic spectrophotometric determination of nitrite is reported based on catalytic effect of nitrite on the redox reaction between sulfonazo III and potassium bromate in acidic media. The reaction was monitored by measuring the decrease in the absorbance of sulfunazo III at 570 nm. Various chemical (such as the effect of acidity, reagents concentrations) and instrumental parameters (flow rate, reaction coil length, injection volume and temperature) were studied and were optimized. Under the optimum conditions calibration graph was linear in the nitrite concentration ranges of 8.00 × 10⁻³-3.00 × 10⁻¹ μg/ml (with slope of 2.40) and 3.50 × 10⁻¹-1.80 μg/ml (with slope of 0.42). The detection limit was 6.00 × 10⁻³ μg/ml of nitrite, the relative standard deviation (n = 10) was 1.25% and 0.88% for 5.00 × 10⁻² and 2.00 × 10⁻¹ μg/ml of nitrite respectively. About 60 samples in 1 h can be analyzed. The interfering effects of various chemical species were studied. The method was successfully applied in the determination of nitrite in food and environmental samples.     

Flow injection analysis of doxycycline or chlortetracycline in pharmaceutical formulations with pulsed amperometric detection

A flow injection with pulsed amperometric detection for determination of doxycycline or chlortetracycline in pharmaceutical formulations is described. Doxycycline or chlortetracycline were studied at a gold rotating disk electrode with cyclic voltammetry as a function of pH of supporting electrolyte solution. The optimized PAD waveform parameters were obtained with a flow injection system. The optimized pulsed conditions of doxycycline were 1150 mV (versus Ag/AgCl reference electrode) detection potential (E_det) for 220 ms (150 ms delay time and 70 ms integration time), 1500 mV (versus Ag/AgCl reference electrode) oxidation potential (E_oxd) for 70 ms oxidation time (t_oxd) and 250 mV (versus Ag/AgCl reference electrode) reduction potentail (E_red) for 400 ms reactivation time (t_red). The optimized pulsed conditions of chlortetracycline were 1050 mV (versus Ag/AgCl reference electrode) detection potential (E_det) for 300 ms (200 ms delay time and 100 ms integration time), 1300 mV (versus Ag/AgCl reference electrode) oxidation potential (E_oxd) for 70 ms oxidation time (t_oxd) and 250 mV (versus Ag/AgCl reference electrode) reduction potentail (E_red) for 400 ms reactivation time (t_red). The optimized PAD waveform was applied to the determination of doxycycline hydrochloride and chlortetracycline hydrochloride standard solution and in pharmaceutical formulations. The linear dynamic ranges of doxycycline hydrochloride and chlortetracycline hydrochloride were 1 μM–0.1 mM. The sensitivity of this method was found to be 23 μA/mM for doxycycline hydrochloride and 33.76 μA/mM for chlortetracycline hydrochloride. The detection limit for both compounds is 1 μM. The doxycycline hydrochloride and chlortetracycline hydrochloride content in commercially available tablet dosage forms by the proposed method was comparable to those specified by the manufacturer.     

Simple flow injection method for simultaneous spectrophotometric determination of Fe(II) and Fe(III)

The method is based on spectrophotometric determination of Fe(II) and Fe(III) at a single wavelength (530 nm) with the use of a dedicated reversed-flow injection system. In the system, EDTA solution is injected into a carrier stream (HNO₃) and then merged with a sample stream containing a mixture of sulfosalicylic acid and 1,10-phenanthroline as indicators. In an acid environment (pH ≅ 3) the indicators form complexes with both Fe(III) and Fe(II), but EDTA replaces sulfosalicylic acid, forming a more stable colourless complex with Fe(III), whereas Fe(II) remains in a complex with 1,10-phenenthroline. As a result, the area and minimum of the characteristic peak can be exploited as measures corresponding to the Fe(III) and Fe(II) concentrations, respectively. The analytes were not found to affect each other's signals, hence two analytical curves were constructed with the use of a set of standard solutions, each containing Fe(II) and Fe(III). Both analytes were determined in synthetic samples within the concentration ranges of 0.05–4.0 and 0.09–6.0 mg L⁻¹, respectively, with precision less than 1.5 and 2.6% (RSD) and with accuracy less than 4.3 and 5.6% (RE). The method was applied to determination of the analytes in water samples collected from artesian wells and the results of the determination were consistent with those obtained using the ICP-OES technique.     

Flow injection catalytic spectrophotometric simultaneous determination of nitrite and nitrate

A new flow injection catalytic spectrophotometric method is proposed for the simultaneous determination of nitrite and nitrate based on the catalytic effect of nitrite on the redox reaction between crystal violet and potassium bromate in phosphoric acid medium and nitrate being on-line reduced to nitrite with a cadmium-coated zinc reduction column. The redox reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique of inserting a reduction column into sampling loop is adopted and the flow injection system produces a signal with a shoulder. The height of shoulder in the ascending part of the peak corresponds to the nitrite concentration and the maximum of the peak corresponds to nitrate plus nitrite. The detection limits are 0.3 ng ml⁻¹ for nitrite and 1.0 ng ml⁻¹ for the nitrate. Up to 32 samples can be analyzed per hour with a relative standard deviation of less than 2%. The method has been successfully applied for the simultaneous determination of nitrite and nitrate in natural waters.     

流动注射光度法测定盐酸普鲁卡因

在盐酸介质中,利用盐酸普鲁卡因－亚硝酸钠－α萘胺的重氨化－偶合反应,建立了流动注射光度法测定盐酸普鲁卡因的新方法。利用控制加 权形心单纯形优化法选择最佳实验条件,测定的线性范围为0－30μg/mL,该法已用于药物中盐酸普鲁卡因含量的测定。     

Flow injection preconcentration by chemofiltration and spectrophotometric determination of Gd

A new on-line Gd preconcentration and determination system associated to flow injection (FI) method was developed. 2,2′-(1,8-dihydroxy-3,6-disulfonaphthylene-2,7-bisazo) bisbenzenearsonic acid (Arsenazo III) was used as a complexing agent at pH 2.5. A reactor containing the polyamide membrane was used for the retention of the Gd complex by chemofiltration. The complex was then removed from the reactor with buffer solution pH 9. The variables affecting the combined on-line preconcentration-absorptiometric method have been evaluated and optimised. The coupling of the on-line preconcentration and spectrophotometric flow through detection led to a detection limit of 15 μg l⁻¹ for a preconcentration time of 5 min at 2 ml/min. The method was successfully applied to biological samples.     

Reverse flow injection spectrophotometric determination of iron(III) using norfloxacin

A reversed flow injection colorimetric procedure for determining iron(III) at the μg level was proposed. It is based on the reaction between iron(III) with norfloxacin (NRF) in 0.07 mol l⁻¹ ammonium sulfate solution, resulting in an intense yellow complex with a suitable absorption at 435 nm. Optimum conditions for determining iron(III) were investigated by univariate method. The method involved injection of a 150 μl of 0.04% w/v colorimetric reagent solution into a merged streams of sample and/or standard solution containing iron(III) and 0.07 mol l⁻¹ ammonium sulfate in sulfuric acid (pH 3.5) solution which was then passed through a single bead string reactor. Subsequently the absorbance as peak height was monitored at 435 nm. Beer's law obeyed over the range of 0.2–1.4 μg ml⁻¹ iron(III). The method has been applied to the determination of total iron in water samples digested with HNO₃–H₂O₂ (1:9 v/v). Detection limit (3σ) was 0.01 μg ml⁻¹ the sample through of 86 h⁻¹ and the coefficient of variation of 1.77% (n=12) for 1 μg ml⁻¹ Fe(III) were achieved with the recovery of the spiked Fe(III) of 92.6–99.8%.     

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.     

New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique

The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength λ = 530 nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic “cut off” peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 2² factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1-3.0 and 0.9-3.5 mg L⁻¹ of both analytes, respectively.     

Flow injection spectrophotometric determination of copper in petroleum refinery wastewaters

This paper reports a new strategy for flow injection spectrophotometric Cu (II) determination in petroleum refinery wastewaters, exploring its reaction with sodium diethyldithiocarbamate (DDTC), without solvent extraction step, thus avoiding the use of harmful organic solvents. The influence of several chemical and flow variables was studied as well as the possible interferences. Under optimized conditions, the flow system was able to process 63 samples per hour, with a detection limit of 23 ng ml⁻¹ and a RSD of 2.1% at the 0.2 μg ml⁻¹ level. In order to attest the accuracy of the methodology, seven samples of effluents were analyzed by the proposed method and the results were compared with that obtained by FAAS. It was observed that the physical interferences verified in the FAAS procedure, which only permits its use by the standard addition method, were not present in the FIA procedure. The results obtained by FIA method were not statistically different from that obtained by FAAS-standard addition method. Also, the analysis of three spiked samples provided recovery percentages between 93 and 103%.     

Determination of trivalent europium using flow injection chemiluminescence method

A simple flow injection chemiluminescence (CL) analysis method for the determination of europium in mineral samples is reported. It is based on luminescence produced by NaIO₄-H₂O₂ CL system sensitized by [Eu(EDTA)]⁻. The relative chemiluminescence intensity of the Eu³⁺-EDTA-NaIO₄-H₂O₂ system is proportional to the amount of Eu³⁺. The optimized experimental conditions were investigated. The linear range and detection limit for Eu³⁺ are 2.0×10⁻⁷ to 1.0×10⁻⁵ and 6.2×10⁻⁸ M, respectively. The sample throughput of the method is 80 samples/h. This method was successfully applied to the determination of europium in rare earth oxides. And the mechanism of chemiluminescence is proposed.     

Sequential injection spectrophotometric determination of trace amounts of iodide by its catalytic effect on the 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction

A simple and sensitive sequential injection spectrophotometric procedure is proposed for the determination of trace amounts of iodide in pharmaceutical preparations. The method is based on the catalytic effect of iodide on the (tetra base) 4,4′-methylenebis(N,N-dimethylaniline)-chloramine-T reaction in acidic solution. The method involves a sequential aspiration of 255 μl sample/standard followed by 170 μl tetra base and then 128 μl chloramine-T solutions into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil towards a detector. The resulting colored compound is measured at 600 nm using an UV/Vis-spectrophotometer. All the parameters that affect the reaction were evaluated and the calibration curve is linear over a range of 0.1–6.0 μg l⁻¹ of iodide concentration with detection limit of 0.05 μg l⁻¹. A sample throughput of 80 samples per hour and relative standard deviation of less than 2.0% was achieved. The method is successfully applied for the determination of iodide in three different samples (tablets).     

Fast simultaneous spectrophotometric determination of naphazoline nitrate and methylparaben by sequential injection chromatography

Fast simultaneous determination of naphazoline nitrate and methylparaben in pharmaceuticals using separation method based on a novel reversed-phase sequential injection chromatography (SIC) is described in this contribution as an alternative to classical HPLC. A Chromolith™ Flash RP-18e (25 mm × 4.6 mm) column (Merck^®, Germany) and a FIAlab^® 3000 system (USA) with a six-port selection valve and 5.0 ml syringe pump were used for sequential injection chromatographic separations in our study. The mobile phase used was methanol/water (40:65, v/v), pH 5.2 adjusted with triethylamine 0.8 μl ml⁻¹ and acetic acid, at flow rate 0.9 ml min⁻¹. UV detection provided by DAD detector and two wavelengths were simultaneously monitored for increasing sensitivity of determination. Detector was set up at 220 nm for naphazoline nitrate and 256 nm for methylparaben and ethylparaben (IS). There is no necessity to use pre-adjustment of sample of nasal drops (only dilution with mobile phase) so the time of the whole analysis is very short. The validation parameters have shown good results: linearity of determination for both components (naphazoline nitrate and methylparaben), correlation coefficient >0.999; repeatability of determination (R.S.D.) in the range 0.5-1.6% at three different concentration levels, detection limits 0.02 μg ml⁻¹ (naphazoline nitrate) and 0.20 μg ml⁻¹ (methylparaben and ethylparaben), and recovery from the pharmaceutical preparations in the range 100.06-102.55%. The chromatographic resolution between peaks of compounds was more than 4.0 and analysis time was less than 4 min under the optimal conditions. The advantages and drawbacks of SIC against classical HPLC are discussed showing that SIC can be an advantageous alternative in many cases.     

Flow injection spectrophotometric determination of vitamin E in pharmaceuticals,milk powder and blood serum using potassium ferricyanide-Fe(Ⅲ) detection system

<正>A simple and sensitive flow injection spectrophotometric method is reported for the determination of vitamin E using potassium ferricyanide-Fe(Ⅲ) detection system.In the presence of vitamin E,Fe(Ⅲ)/ferricyanide reduces.The in situ reduced ions are then reacted with unreduced portion of ferricyanide/Fe(Ⅲ) to make soluble Prussian blue,which is monitored at absorption wavelength of 735 nm.Linear calibration graph was obtained in the concentration range of 0.1-40μg mL~(-1).The relative standard deviations (n=4) were in the range of 1.1-3.6%,with limits of detection(3 s blank) of 0.04μg mL~(-1).The proposed method allowed 12 injections h~(-1).The method is applied to determine vitamin E in pharmaceuticals,infant milk and blood serum samples using hexane extraction with the recoveries in the range of 93±3 to 97.5±4%.The method is validated using certified reference materials SRM 968c for blood serum samples.     

Flow-injection chemiluminescence determination of chlortetracycline using on-line electrogenerated [Cu(HIO(6))(2)](5-) as the oxidant

A novel chemiluminescence (CL) flow system for the determination of chlortetracycline is described. It is based on the direct CL reaction of chlortetracycline and [Cu(HIO₆)₂]⁵⁻ in KOH medium. The unstable [Cu(HIO₆)₂]⁵⁻ was on-line electrogenerated by constant-current electrolysis. The CL intensity was linear with chlortetracycline concentration in the range of 0.1–100 μg ml⁻¹. The determination limit was 5.3×10⁻⁸ g ml⁻¹. The whole process could be completed in 1 min. The proposed method is suitable for automatic and continuous analysis, and has been applied satisfactorily to analysis of chlortetracycline in biological fluid.     

A novel spectrophotometric method for batch and flow injection determination of sulfite in beverages

A novel spectrophotometric assay method for batch and flow injection determination of sulfite in beverages is described. The method involves a reaction with diaquacobyrinic acid heptamethyl ester (diaquacobester, DACbs) in acetate buffer of pH 3 to form a highly stable sulfite cobester complex (SO₃Cbs). In the absence of sulfite, the reagent displays three absorption maxima at 349, 409 and 525 nm. Addition of sulfite is associated with the development of a new absorption band at 313 nm, an increase in the intensity of the band at 425 nm and a decrease in the absorbance of the bands at 349 and 525 nm. Variations of the absorptions at 313, 349, 425 and 525 nm are linearly proportional to sulfite concentrations over the range of 0.05–25 μg ml⁻¹with a detection limit of 0.01–0.2 μg ml⁻¹. Negligible interferences are caused by most common ions. Validation of the method according to the quality assurance standards shows suitability for quality control assessment of sulfite in complex matrices without prior treatment. The method has the advantages of high selectivity, good sensitivity, fast reaction, high stability of the reagent and reaction product and absorbance measurements at four different wavelengths in the same run. The method is successfully applied to determine the sulfite contents of some beverages. The results compare fairly well with data obtained using the standard method.     

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.     

Flow injection spectrophotometric determination of fosfestrol, following on-line thermal induced digestion and using an orthophosphate calibration graph

A novel flow injection (FI) system for the spectrophotometric determination of diethyl stilbestrol diphosphate (fosfestrol) in pharmaceutical formulations is described. On-line thermal induced digestion of the analyte by peroxodisulfate ion was performed and the orthophosphate ion generated was determined spectrophotometrically (λ_max=690 nm) using a molybdenum blue based FI approach. As the achieved conversion of the analyte was quantitative, an orthophosphate calibration graph can be used for its determination as well. The chemical and FI variables affecting the digestion were investigated. A linear calibration graph was obtained in the range 5.0×10⁻⁷-1.0×10⁻⁴ mol l⁻¹ fosfestrol. The relative standard deviation was very good (s_r=0.8% at 5.0×10⁻⁵ mol l⁻¹ fosfestrol, n=12) and the 3σ detection limit was 2.5×10⁻⁷ mol l⁻¹. The sampling rate was 60 injections h⁻¹. The average accuracies for the determination of the analyte in a pharmaceutical formulation evaluated by comparison of the results with those obtained by the supplier (Asta Medica) and the method recommended by the US Pharmacopoeia were also very good (e_r of +0.8 and −0.3%, respectively). Average recoveries of known amounts of the analyte ranging between 97.9 and 100.8% were also obtained.