A green analytical procedure for sensitive and selective determination of iron in water samples by flow-injection solid-phase spectrophotometry

A greener analytical procedure based on flow-injection solid-phase spectrophotometry is proposed for iron determination. Iron(II) is reversibly retained on 1-(2-thiazolylazo)-2-naphthol immobilized on C18-bonded silica, yielding a brown complex. The metal ion is eluted as iron(II) with a small volume of a diluted acid solution without removing the immobilized reagent, which can be used for at least 100 determinations. Other chemicals (buffer and reducing agent) were carefully selected taking into account the analytical performance and toxicity. The developed procedure is 10-fold more sensitive in comparison to the analogous procedure based on measurements in solution, being suitable for the determination of iron in water samples with good accuracy and precision. The detection limit (99.7% confidence level), sampling rate and coefficient of variation (n = 10) were estimated as 15 μg L⁻¹, 25 measurements per hour and 4.0%, respectively. The proposed procedure involves a reduced effluent generation (3.6 mL per determination) and consumes micro amounts of reagents.     

Simultaneous determination of formaldehyde and methanol by flow-injection catalytic spectrophotometry

A flow-injection method is proposed for the simultaneous catalytic determination of formaldehyde and methanol on the basis of the catalytic action of formaldehyde upon the redox reaction between crystal violet and potassium bromate in a phosphoric acid medium and on-line oxidization of methanol into formaldehyde using a lead dioxide solid-phase reactor. The indicator reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique based on three sampling loops with a single injection valve is developed. The flow-injection system produces a signal of main peak with two shoulders of the same height. The height of the shoulders corresponds to the formaldehyde concentration, and the height difference between the shoulders and the main peak corresponds to the methanol concentration. The detection limit is 0.1 μg/mL for formaldehyde and 1.0 μg/mL for methanol with the sampling rate of 10 samples per hour. The relative standard deviations for 11 replicate determinations of formaldehyde (1.0 μg/mL) and methanol (10 μg/mL) are 1.1 and 2.1%, respectively. The method has been successfully applied to the simultaneous determination of formaldehyde and methanol in some gas samples. The text was submitted by the authors in English.     

Rapid determination of zinc and iron in foods by flow-injection analysis with flame atomic-absorption spectrophotometry and slurry nebulization

A rapid method of determining zinc and iron in food by flame atomic-absorption spectrophotometry with slurry nebulization into an air-acetylene flame has been developed. A V-groove, clog-free Babington-type nebulizer, coupled to a single-line flow-injection analysis (FIA) system, was employed to introduce the slurry into the spray chamber. Under the FIA conditions described, an injection frequency of 120/hr is possible, with negligible carry-over and memory effects. The calibration graphs were obtained by using various concentrations (up to 0.1 g/ml) of white bean homogenate as standards, rather than solutions. The method has been applied to various kinds of foods, including grains, vegetables, fruits and sausage. Homogenization of semi-prepared samples to form slurries took only 4 min. Relative deviations between results by the slurry and solution methods for both elements averaged 2-3%. Detection limits by the slurry method were 0.3 mug/ml Zn and 0.6 mug/ml Fe.     

流动注射催化动力学光度法测定碘离子

Based on catalysis of I- on the decolor reaction between potassium bromate and indigo carmine in the acid medium,and combined with flow injection analysis,a new flow-injection catalytic kinetic spectrophotometric method was found for determination of iodide in sample.The experimental results show that the determination is carried out at temperature of 80℃ and the concentration of H_2SO_4,KBrO_3,and indigo carmine is 1.2 mol/L,1.8×10~(-2) mol/L and 1.0×10~(-4) mol/L respectively,the linear range for the method is 0.50～1.8 mg/L.The detection limit is 0.0022 mg/L.The relative standard deviation is 1.92%.The proposed method was applied to the determination of iodide in troche successfully.The recovery was between 99.2% and 103.6%.     

Indirect determination of ascorbic acid by solid-phase spectrophotometry

Solid-phase spectrophotometry (SPS) technique, in the visible region, was used for the spectrophotometric determination of ascorbic acid based on the reducing effect on iron(III) ion, followed by formation of the iron(II)-ferrozine chelate. The chelate is easily sorbed on a dextran-type anion-exchange gel and the absorbance of the resin at 567 and 800 nm, packed in a 1 mm cell, is measured directly. The apparent molar absorptivity using 100 ml of sample was 2.1×10⁷ l mol⁻¹ cm⁻¹ and it allowed the determination of ascorbic acid in the range 5–90 ng ml⁻¹; the detection limit was 0.91 ng ml⁻¹ and the RSD 0.91% for a concentration of 50 ng ml⁻¹ of ascorbic acid (n=10). The proposed method permits a highly sensitive and selective determination of ascorbic acid without any preconcentration and it has been satisfactorily applied for its determination in fruit juices, pharmaceuticals, urine and conservative liquids.     

An improved flow system for chloride determination in natural waters exploiting solid-phase reactor and long pathlength spectrophotometry

A single and sensitive spectrophotometric method for chloride ions determination based on a commuted flow system with a 100 cm optical path flow cell and a solid-phase reactor containing immobilized silver chloranilate was proposed. This procedure exploited the AgCl formation in the solid-phase reactor leading the chloranilate ions, monitored spectrophotometrically at 530 nm. The analytical signals were 75-fold higher and the sensitivity was 12-fold than that achieved with a 1 cm flow cell, allowed a chloride determination in the 0.5-100 mg l⁻¹ range. The R.S.D. was 1.1% (n = 20) with a sample throughput of 80 h⁻¹ and a waste generated of ca. 100 ng of chloranilate ions per determination. Four samples of natural waters from São Carlos and Araraquara cities were evaluated using the proposed method. Results agreed with the obtained by a reference method at the 95% confidence level.     

Rapid continuous determination of aluminium in copper-base alloys by flow-injection spectrophotometry

Summary A flow-injection spectrophotometric method has been developed for the rapid, continuous determination of aluminium in copper-base alloys. The system consists of the masking of copper, zinc, iron, etc. with a combined use of thiourea, ascorbic acid and EDTA and the measurement of light absorption of aluminium-Xylenol Orange complex at 506 nm. With appropriate standardization satisfactory results are obtained in spite of sluggish reaction of aluminium and Xylenol Orange. The system allows the analysis of solutions of copper-base alloys for aluminium to be conducted at a rate of 50 determinations per hour without any carryover. The results obtained for standard brasses and aluminium bronze (Al 1.43–10.2%) agreed well with the certified values. The precision (rsd) ranges are 0.2–0.3%.

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Kontinuierliches Schnellverfahren zur Bestimmung von Aluminium in Kupferlegierungen mit Hilfe der Flow-Injection-Spektralphotometrie

Zusammenfassung Bei dem empfohlenen Verfahren werden Cu, Zn, Fe und andere Störelemente mit Hilfe von Thioharnstoff, Ascorbinsäure und EDTA maskiert und der Al-Xylenolorange-Komplex bei 506 nm gemessen. Mit Hilfe eines geeigneten Eichverfahrens werden trotz der trägen Reaktion von Al mit Xylenolorange zufriedenstellende Werte erhalten. 50 Bestimmungen können innerhalb von 1 h ohne jedes Verschleppen durchgeführt werden. Bei der Analyse von Messing und Al-Bronze (1,43–10,2% Al) wurde gute Übereinstimmung mit zertifizierten Werten erzielt. Die Standardabweichungen lagen im Bereich von 0,2–0,3%.

     

Catalytic determination of molybdenum in plants by flow-injection spectrophotometry with ion-exchange separation

The catalytic effect of molybdenum n the oxidation of iodide by hydrogen peroxide is utilized. A cation-exchange resin column is incorporated into the system to remove interfering ions; during sample processing, the interfering ions are eluted towards waste. Plant materials are ashed and solutions are injected. The proposed system can handle about 40 samples per hour with molybdenum contents in the 1.0–40.0 μg 1^?1 range. Results are precise (r.s.d. usually <%) and in agreement with those obtained by graphite-furnace atomic absorption spectrometry.     

Determination of paraquat by flow-injection spectrophotometry

The flow-injection determination of Paraquat (1,1′-dimethyl-4,4′-bipyridinium) is based on its reduction with sodium dithionite in alkaline medium and detection at 605 nm. Linear calibration plots are obtained for 0.1–1.0, 1.0–10 and 5.0–30.0 mg l^?1 Paraquat, the lower limit being 40 times less than that of the usual spectrophotometric method. The method is applied to determine Paraquat in spiked potable water and potatoes after preconcentration by column ion-exchange. The determination of Paraquat in different herbicide samples yielded results in good agreement with those obtained by polarographic and manual spectrophotometric methods.     

Simultaneous determination of traces of heavy metals by solid-phase spectrophotometry

A coupling sensitive solid phase spectrophotometric (SPS) procedure for determination of traces of heavy metals (Me-SPS) and multicomponent analysis by multiple linear regressions (MA), a simple methodology for simultaneous determination of metals in mixtures was inaugurated. The Me-SPS procedure is based on sorption of heavy metals on PAN-resin and direct absorbance measurements of colour product Me-PAN sorbed on a solid carrier in a 1-mm cell. This methodology (Me-SPS-MA) was checked by simultaneous determination of metals in synthetic mixtures with different compositions and contents of metals important in pharmaceutical practice: Zn, Pb, Cd, Cu, Co, and Ni. Good agreement between experimental and theoretical amounts of heavy metals is obtained from the recovery test (78.3–110.0%). The proposed method enables determination of particular metal ion at the ng mL⁻¹ level and it was successfully applied to the determination impurities from heavy metal traces in pharmaceutical substances (Cu in ascorbic acid, Pb in glucose, and Zn in insulin). The proposed procedure could be possible contribution to the development of pharmacopoeial methodology for a heavy metals test.     

The trace determination of some heavy metals in waters by flow-injection spectrophotometry and potentiometry

Three automated flow-injection systems are proposed for the determination of traces of manganese(II), lead and copper(II) in waters. The first system utilizes the catalytic effect of manganese(II) on the oxidation of N,N-diethylaniline by potassium periodate at pH 6.86–7.10 (30°C) and is used for spectrophotometric determination at 475 nm in the range 0.02–1.00 μg1^?1; the system involves reagent injection and stopped flow. The determination of lead in the range 0.7–100 μg1^?1 is based on spectrophotometric detection of the lead 4/(2-pyridylazo)resorcinol complex at 525 nm after on-line preconcentration of the sample (5–50 ml) on a minicolumn filled with Chelex-100 or Dowex 1-X8 resin. A potentiometric flow-injection system with a copper ion-selective electrode is applied for the determination of 0.5–1000 μg 1^?1 copper(II) after on-line preconcentration of 50–500 ml of sample on Chelex-100 resin. The procedures are tested on synthetic and real water samples, including sea water and waste-waters.     

Development and prevalidation of a method for phenol determination by solid-phase spectrophotometry

A simple, sensitive and rapid solid-phase spectrophotometric procedure was developed for the determination of traces of phenol with 4-aminoantipyrine as a reagent (AAP-SPS), and the optimal experimental conditions were established. This method was performed by sorption and direct absorbance measurements of the product phenol-AAP sorbed on the anion-exchanger Dowex 1-X4 (0.2 g) at 495 nm (absorption maximum) and 700 nm (non-absorption wavelength). The sensitivity offered by the AAP-SPS procedure was higher by a factor of 40 compared with the respective conventional spectrophotometric method. Metrological characteristics were established using a prevalidation strategy. The AAP-SPS procedure is characterized by a linear calibration function in the working range of 0.05–0.50 μmol, low standard deviation of procedure (±0.012), low limit of determination (0.021 μmol), and favorable random (±0.85 to ±11.27%) and systematic deviations (−4.55 to +11.50%). Moreover, the accuracy of the system investigated by the recovery test is acceptable (99–102%). Favorable working and performance characteristics make the new SPS method ideal for phenol monitoring in pharmaceutical preparations as well as other matrices.     

The determination of Nickel in Iron and Steel by Atomic absorption spectrophotometry

A procedure is described for the determination of 0.005 to 2% of nickel in low and high alloy irons and steels by atomic absorption spectrophotometry. The sample is dissolved in phosphoric-sulphuric acid and atomised in an atomic absorption spectrophotometer. The method is rapid and free from interferences; preliminary separations are not required and results obtained on standard samples are in good agreement with certificate values.     

Simultaneous determination of iron and zinc by pH gradient construction in a flow-injection system

A flow-injection method for the simultaneous determination of iron and zinc in the human hair with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) using a pH gradient technique has been developed. The linear range for the determination of iron is 0.1 approximately 1.8 mug ml(-1) and for zinc is 0.2 approximately 5.0 mug ml(-1). About 20 approximately 30 samples can be determined in 1 h. The proposed method is simple, rapid and accurate. It has been applied to the simultaneous determination of trace amounts of iron and zinc in the human hair with satisfactory results.     

Simultaneous determination of quinoline yellow and brilliant blue FCF in cosmetics by solid-phase spectrophotometry

A method for the simultaneous determination of quinoline yellow (QY) and brilliant blue FCF (BB) in mixtures by solid-phase spectrophotometry has been developed. Both colorants were isolated in Sephadex DEAE A-25 gel showing maximum absorbances at 632 nm and 415 nm for BB and QY respectively. The applicable concentration ranges were between 25.0 and 500.0 mug 1(-1) for BB and between 50.0 and 750.0 mug 1(-1) for QY. The detection limits were 6.1 and 13.4 mug (-1) for BB and QY respectively. Application of the method to real samples (colognes, after shave lotions and shampoo gels) involves a previous extraction process of the colorants before their isolation on the gel.     

Simultaneous flow-injection determination of aluminium and zinc using LED photometric detection

A flow photometer with a multi-LED detector was applied to the simultaneous determination of aluminium and zinc with microcomputer control of photometric measurements and data processing. Xylenol Orange is the photometric reagent and the reaction is carried out in acetate buffer. Calibration graphs are linear for both metals in the concentration ranges 0.2–25 μg ml^?1 (Al) and 0.2–30 μg ml^?1 (Zn). Both elements can be determined for Al to Zn ratios varying from 0.01 to 100 with r.s.d. 1.1 and 1.4%, respectively. The method developed was applied to the determination of Al and Zn in alloys.     

An improved flow system for phenols determination exploiting multicommutation and long pathlength spectrophotometry

A greener and sensitive procedure for spectrophotometric determination of phenols based on a multicommuted flow system with a 100 cm optical path flow cell is presented. The method exploited the oxidative coupling of phenolic compounds with 4-aminoantipyrine in alkaline medium containing potassium hexacyanoferrate(III). Sensitivity was 80-fold higher than that achieved with a 1 cm flow cell, making feasible the determination of phenols in the 10-100 μg l⁻¹ range with a detection limit estimated as 1 μg l⁻¹ phenol. The sampling rate and the coefficient of variation were estimated as 90 determinations per hour and 0.6% (n=10), respectively. The multicommutation approach allowed a 200-fold reduction of the reagent consumption in comparison with the reference batch method. Moreover, the chloroform extraction for analyte concentration is unnecessary in view of the increase in sensitivity. Recoveries within 93.3 and 106% were achieved for determination of phenol in natural and wastewater samples. Results agreed with the obtained by a reference method at the 95% confidence level.     

Determination of beryllium in copper-beryllium alloys by flow-injection spectrophotometry

Summary A method is described for the flow-injection spectrophotometric determination of beryllium in Cu-Be-alloys using xylenol orange as reagent. Cu, Co and Fe are masked by means of thiosulphate and EDTA. Absorbance is measured at the maximum of 493 nm. With a flow rate of 4 ml/min 60 samples can be analyzed per hour with a relative standard deviation of about 1%.

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Bestimmung von Beryllium in Cu-Be-Legierungen durch Flow-Injection-Spektralphotometrie

Zusammenfassung Als Reagens zur spektralphotometrischen Bestimmung von Berryllium in Cu-Be-Legierungen dient Xylenolorange. Cu, Co und Fe werden mit Hilfe von Thiosulfat und EDTA maskiert. Die Messung erfolgt im Absorptionsmaximum des Komplexes von 493 nm. Bei einer Durchflußgeschwindigkeit von 4 ml/min können 60 Proben je Stunde mit einer relativen Standardabweichung von etwa 1% analysiert werden.

     

Magnetic solid-phase extraction of Zineb by C18-functionalised paramagnetic nanoparticles and determination by first-derivative spectrophotometry

Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles have been synthesised and used as magnetic solid-phase extraction (MSPE) sorbent for the extraction of Zineb from agricultural aqueous samples under ultrasonic condition and quantified through a first-derivative spectrophotometric method. The produced magnetic nanoparticles were characterised by using scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and zeta potential reader. The Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles had spherical structures with diameters in the range of 198–201 nm. Further, MSPE was performed by dispersion of Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles in a buffered aqueous solution accompanied by sonication. Next, the sorbents were accumulated by applying an external magnetic field and were washed with 4-(2-pyridylazo) resorcinol-dimethyl sulfoxide solution, for the purpose of desorbing the analyte. The extraction conditions (sample pH, washing and elution solutions, amount of sorbents, time of extraction, sample volume and effect of diverse ions), as well as Zineb-PAR first-order derivative spectra, were also evaluated. The calibration curve of the method was linear in the concentration range of 0.055–24.3 mg L^?1 with a correlation coefficient of 0.991. The limit of detection and limit of quantification values were 0.022 and 0.055 mg L^?1, respectively. The precision of the method for 0.27 mg L^?1 solution of the analyte was found to be less than 3.2%. The recoveries of three different concentrations (0.27, 1.37 and 13.7 mg L^?1) obtained 98.3%, 98.5% and 96.0%, respectively. The proposed Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles were found to have the capability of reusing for 7.0 times.     

Continuous spectrophotometric determination of copper, nickel and zinc in copper-base alloys by flow-injection analysis

Flow-injection methods have been developed for the determination of copper, nickel and zinc in copper-base alloys, including several types of brasses, deoxidized copper, beryllium copper and German silver. The system for copper and nickel involves the measurement of the absorbance of the copper(II) and nickel(II) aquo-complexes at 805 and 410 nm, respectively, after simple dissolution of the sample in a nitric acid-phosphoric acid mixture. The system needs no further reagents and the sample solutions can be analysed at rates of up to 280 /hr for copper (or nickel in German silver) without any carry-over. The system for zinc consists of automatic dilution of the injected sample with a thiosulphate-acetate buffer solution and the subsequent measurement of the absorbance of the zinc-Xylenol Orange complex at 568 nm. This system permits analysis rates of up to 90/hr for zinc solutions, with no carry-over. The procedures have been applied to standard copper-base alloys. The results agreed satisfactorily with the certified values. The precision ranges are 0.2-0.7% for copper and nickel and 0.5-0.8% for zinc.