Separation and preconcentration of Se(IV)/Se(VI) speciation on algae and determination by graphite furnace atomic absorption spectrometry in sediment and water

A novel method for the separation and preconcentration of Se(IV)/ Se(VI) with algae and determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The Se(VI) is extracted with algae from the solution containing Se(IV)/Se(VI) at pH 5.0, and the remaining Se(IV) is then preconcentrated pH 1.0. The detection limits (3σ, n = 11) of 0.16 μg L^–1 for Se(IV) and 0.14 μg L^–1 for Se(VI) are obtained using 40 mL of solution. At the 2.0 μg L^–1 level the relative standard deviation is 2.6% for Se(IV) and 2.3% for Se(VI). The method has been applied to the determination of Se(IV)/Se(VI) in sediment and water samples. Analytical recoveries of Se(IV) and Se(VI) added to samples are ?97 ± 5% and 102 ± 6% (95% confidence), respectively. Received: 10 February 1999 / Revised: 21 June 1999 / /Accepted: 22 June 1999     

Kinetic-Spectrophotometric Determination of Tellurium (IV) by Its Catalytic Effect on the Reduction of Thionine by Sodium Sulfide in Cationic Micellar Medium

A simple and highly sensitive method is proposed for the determination of Te(IV) by its catalytic effect on the reduction of thionine by sodium sulfide in the presence of cetyl trimethyl ammonium bromide as a micelle media. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 600 nm with a fixed time of 0.5-2.5 min from initiation of the reaction. Tellurium can be measured in the concentration range of 0.6-500.0 ng/mL, with a limit of detection of 0.3 ng/mL Te(IV). The influence of more than thirty potential interfering ions was studied on the determination of tellurium. The relative standard deviation for ten replicate measurements of 0.020 and 50.0 ng/mL Te(IV) was 2.1 and 1.9%, respectively. The method was applied for the determination of tellurium in synthetic samples.     

Determination of trace titanium with titanium(IV)-(DBC-arsenazo)-potassium bromate system by catalytic-kinetic spectrophotometry

In a 0.080 M sulphuric acid medium, trace titanium(IV) catalyzes the discoloring reaction of DBC-arsenazo oxidized by potassium bromate and the discoloring degree is proportional to the concentration of titanium(IV) in the solution. A new catalytic-kinetic spectrophotometric method for the determination of trace titanium(IV) was developed based on this principle. At a wavelength of 516 nm, the linear range of determination of titanium(IV) is 0–2.2 μg/25 mL. The detection limit for the determination of titanium is 2.04 ng/mL. The present method has been satisfactorily applied to the determination of titanium in fish samples. The text was submitted by the authors in English.     

Spectrophotometric determination of traces of selenium(IV) in various environmental samples using the flow-injection technique (FIT)

A simple, sensitive, and rapid flow-injection spectrophotometric method was developed for the determination of trace amounts of selenium(IV). The method is based on the oxidation reaction of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) by selenium(IV) followed by the coupling reaction with chromotropic acid (4.5-dihydroxy naphthalene-2.7-disulphonic acid) in a basic medium (phosphate buffer, pH 10.5) to give a pink derivative with λ_max 530 nm that is stable for more than 7 days at 35°C. The reaction and flow conditions of the full experimental design were optimized. A detection limit (2s) of 0.25 μg/L Se(IV) was obtained at a sampling rate of 10 samples per hour. Beer’s law is obeyed for a Se(IV) concentration range of 0.05–0.5 μg/mL at the wavelength of maximum absorption. The detailed study of various interference ions indicates that the method is highly selective. The method was successfully applied to the determination of traces of selenium(IV) in various water samples. The results obtained were in good agreement with those obtained by the reported methods at the 95% confidence level. The text was submitted by the authors in English.     

Kinetic spectrophotometric determination of trace amounts of selenium based on the catalytic reduction of maxilon blue-SG by sulfide

A simple and sensitive catalytic spectrophotometric method was developed for the determination of trace amounts of selenium. The method is based on the catalytic effect of selenium in form Se(IV) on the reduction of Maxilon Blue-SG by sodium sulfide. Indicator reaction is followed spectrophotometrically by measuring the absorbance change at λ_max=654 nm and constant temperature (30.0±0.1 °C) by fixed time method. Selenium could quantitatively be determined in the range 0.004-0.200 μg ml⁻¹ Se(IV) with a detection limit of 0.205 ng ml⁻¹ Se(IV). All of the variables that affected the reaction rate were investigated and established optimum conditions to give maximum sensitivity. The R.S.D.s of the method (N=12) for the Se(IV) concentrations of 0.004, 0.016, 0.040 and 0.160 μg ml⁻¹ are between 2.27 and 0.32%, respectively, and depended on Se(IV) concentration. The interference effect of various anion and cations on the Se(IV) determination was also fully studied. The selectivity of catalytic reaction was greatly improved with the use of the strong cation exchange resin. The developed kinetic-catalytic reaction was applied to the determination of selenium in real samples as Antioxidant-S, Selsun (which is a healthcare product for the treatment of dandruff) and analytical grade sodium metabisulfite, and in spring water samples without any pre-concentration. The acceptable recoveries were obtained by the method for appropriate standard Se(IV) additions. The method is simple, practical and suitable for using in small laboratories owing to its precision, sensitivity and relative selectivity.     

Spectrophotometric determination of palladium(II) based on its catalytic effect on the reduction of azure I by sodium hypophosphite

A catalytic-spectrophotometric method for the determination of traces of palladium(II) is proposed. The reaction is based on the catalytic action of palladium(II) on the reduction of azure I (λ_max = 647 nm) by sodium hypophosphite. The various variables affecting the sensitivity were studied, and a study of interfering ions was also carried out. The reaction gave a detection limit of 4.3 ng/mL palladium(II) and good reproducibility with a relative standard deviation of 1.53–1.98% in the palladium(II) concentration range 40–200 ng/mL. The method yielded another linear range (5–40 ng/mL) when using slightly different conditions. In this case, the detection limit was 0.78 ng/mL palladium(II), and the relative standard deviation for ten replicate analyses of 20 ng/mL palladium(II) was 2.05%. The method was applied to the determination of palladium in a sample of activated charcoal. The text was submitted by the authors in English.     

Kinetic spectrophotometric determination of traces of iron(II)

A simple method for the selective and sensitive kinetic spectrophotometric determination of iron (II) is described. The method is based on the oxidation reaction of reduced phenolphthalein by periodate in alkaline media. The change in absorbance was measured using the fixed time method. The effect of different variables on the reaction was investigated and optimum conditions were obtained. The calibration curve was linear in the range 50–3000 ng/mL, and a detection limit of 17 ng/mL was obtained. The relative standard deviation of ten replicate determinations of 200 ng/mL of Fe(II) was 1.2%. The determination of Fe(II) in the presence of a 50-fold amount of Fe(III) could be carried out. This article was submitted by the authors in English.     

Kinetic Spectrophotometric Method for the Determination of Rhodium by Its Catalytic Effect on the Oxidation of O-Toluidine Blue by Periodate in Micellar Media

A simple kinetic spectrophotometric method was developed for the determination of ultra trace amounts of Rh(III). The method is based on the catalytic effect of rhodium(III) on the oxidation of o-Toluidine blue by periodate in micellar media. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of o-Toluidine blue at 628 nm with a fixed-time method. The decrease in the absorbance of o-Toluidine blue is proportional to the concentration of Rh(III) in the concentration range 1.0–400.0 ng/mL, with a fixed time of 0.5–4.5 min from initiation of the reaction. The limit of detection is 0.2 ng/mL Rh(III). The relative standard deviation for the determination of 0.020 and 0.100 g/mL Rh(III) was 2.2 and 1.5%, respectively. The method was applied to the determination of rhodium in water.     

Kinetic determination of selenium using the reduction of nile blue with sulfide ions

The catalytic effect of Se(IV) was first observed in the reaction of the reduction of Nile Blue with sulfide ions. Optimal conditions for the determination of selenium by this reaction were found. The dependence of the reaction rate on the concentration of Se(IV) was linear in the concentration range 0.008-0.16 μg/mL. Solvent extraction with dithiophosphoric acids was proposed for the separation of selenium from the interferents. A procedure for the extraction-kinetic determination of selenium with the detection limit 0.006 μg/mL was developed.     

Kinetic spectrophotometric determination of trace amounts of selenium and vanadium

A sensitive kinetic spectrophotometric method has been developed for the determination of Se(IV) over the range of 45 to 4000 ng in 10 mL of solution. The method is based on the catalytic effect of Se(IV) on the reduction reaction of bromate by hydrazinium dichloride, with subsequent reaction of Ponceau S with products of the above reaction (chlorine and bromine), causing color changing of Ponceau S. Method development includes optimization of time interval for measurement of slope, pH, reagents concentration, and temperature. The optimized conditions yielded a theoretical detection limit of 33 ng/¶10 mL of solution of Se(IV). The interfering effects were studied and removed. The method was applied to the determination of selenium in spiked water, Kjeldahl tablet, selenium tablet, and shampoo. Vanadium(V) has an inhibition effect on the catalyzed reaction of bromate and hydrazine by selenium. Using this effect, V(V) can be determined in the range of 70 to 2500 ng in 10 mL of solution. The optimization procedure includes pH and selenium concentration. An extraction method was used for interference removal. The method was applied to the determination of vanadium in petroleum.     

Catalytic determination of ultra trace amounts of palladium by linear sweep voltammetry

A sensitive method is proposed for the determination of palladium, based on its catalytic effect on the reduction of malachite green by hypophosphite. The reaction rate is monitored by measuring the current of product of reaction at −0.79 V vs. Ag/AgCl reference electrode. The linear dynamic range is 30.0–300.0 ng/mL with a limit of detection of 10.0 ng/mL. The interference effects of many ions were studied. The method was used for the determination of Pd(II) in synthetic samples of dental alloys with satisfactory results.     

Sensitive reaction rate method for the determination of low levels of formaldehyde with photometric detection

A simple and rapid method is proposed for the determination of ultra trace amounts of formaldehyde. It is based on the catalytic effect of formaldehyde on the oxidation of Brilliant cresyl blue by bromate. The reaction is monitored photometrically by measuring the decrease in absorbance of the dye. Formaldehyde in the range of 0.005–2.300 μg/mL can be determined with a limit of detection of 0.003 μg/mL. The relative standard deviation for ten replicate measurements of 1.5 μg/mL formaldehyde is 0.1%. The method was used for the determination of formaldehyde in real samples with satisfactory results. Received: 26 May 1998 / Revised: 30 September 1998 / Accepted: 3 October 1998     

Determination of lead traces in water and liqueurs by derivative atom trapping flame atomic absorption spectrometry

 A new method for the direct determination of lead traces using derivative atom trapping flame atomic absorption spectrometry (DAT-FAAS) with an improved water-cooled stainless steel trapping equipment in an air-acetylene flame was investigated. The optimum conditions concerning the sensitivity were studied. For a 1 min collection, the characteristic concentration (given as derivative absorbance of 0.0044) and the detection limit (3s) were 1.4 ng/mL and 0.27 ng/mL, respectively. This is 361 and 74-fold better than those of the conventional flame atomic absorption spectrometry (FAAS) and comparable to those of graphite furnace atomic absorption spectrometry (GFAAS). The detection limit and sensitivity of DAT-FAAS for a 3 min collection time were 2 and 3 orders of magnitude higher than those of conventional FAAS. The present method was applied to the determination of lead in water and liqueur samples with a recovery range of 94–108% and a relative standard deviation of 3.5–5.6%. Received: 10 January 1996/Revised: 9 December 1996/Accepted: 20 December 1996     

Separation and determination of selenium in water samples by the combination of APDC coprecipitation: X-ray fluorescence spectrometry

A sensitive and non chromatographic analytical procedure for the separation of inorganic selenium species in natural water has been performed. A combination of APDC coprecipitation and determination by an absolute thin layer Energy dispersive X-ray fluorescence spectrometry method was used. The influence of various analytical parameters such as element concentration, oxidation states and pH on the recoveries of Se (IV) was examined. The presence of organic matter and bicarbonate anions, typical components in Cuban groundwater samples, was also tested. Negligible matrix effects were observed. At pH 4 a 100% recovery was found for Se (IV). The coprecipitation recovery of the oxidized selenium species (Se (VI)) was null for the selected concentration range (5–100 μg L⁻¹). When the Se (VI) was reduced by heating the solution with 4 mol L⁻¹ HCl, quantitative recovery was also obtained. The determination of total selenium was conducted by the application of the oxidation–reduction process and the analytical procedure for Se (IV). Se (VI) content was calculated as the difference between total selenium and Se (IV). The detection limit was 0.13 μg L⁻¹. The relative standard deviation was lower than 3.5% for 5 μg L⁻¹ of Se (IV). The trueness of the method was verified by using standardized hydride generation-atomic absorption spectrometry technique. The results obtained using the EDXRF technique were in good agreement with the ones determined by HG-AAS. The proposed method was applied to the determination of Se (IV) in surface water and groundwater samples.     

Highly sensitive spectrophotometric determination of olanzapine using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl

Two highly sensitive spectrophotometric methods have been developed for the determination of olanzapine (OLP) in pharmaceuticals using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl as reagents. The methods are based on the oxidation of OLP in acidic medium by a known excess of cerium(IV) followed by the determination of the unreacted oxidant by reacting with either ferroin and measuring the absorbance at 510 nm (method A) or iron(II)-2,2′-bipyridyl complex and measuring the absorbance at 525 nm (method B). The amount of cerium(IV) reacted corresponds to the amount of OLP. In both the methods, the absorbance is found to increase linearly with OLP concentration as shown by the correlation coefficient (r) of 0.9980 and 0.9958 for method A and method B, respectively. The calibration graphs are linear over the concentration range of 0.2–2.0 μg/mL in both the methods. The calculated molar absorptivity values are 1.00 × 10⁶ and 7.03 × 10⁵ L/mol cm, for method A and method B. The LOD and LOQ values for method A are calculated to be 0.04 and 0.13 μg/mL and the values are 0.07 and 0.22 μg/mL for method B, respectively. The methods were validated as per the current ICH guidelines. Both the methods gave similar results in terms of accuracy and precision. The RSD was less than 3% and the accuracy, obtained from recovery experiments, was 98.76–101.4%. The methods developed were applied to the determination of OLP in tablets and results agreed well with the label claim.     

Kinetic spectrophotometric determination of trace amounts of selenium and vanadium

A sensitive kinetic spectrophotometric method has been developed for the determination of Se(IV) over the range of 45 to 4000 ng in 10 mL of solution. The method is based on the catalytic effect of Se(IV) on the reduction reaction of bromate by hydrazinium dichloride, with subsequent reaction of Ponceau S with products of the above reaction (chlorine and bromine), causing color changing of Ponceau S. Method development includes optimization of time interval for measurement of slope, pH, reagents concentration, and temperature. The optimized conditions yielded a theoretical detection limit of 33 ng/?10 mL of solution of Se(IV). The interfering effects were studied and removed. The method was applied to the determination of selenium in spiked water, Kjeldahl tablet, selenium tablet, and shampoo. Vanadium(V) has an inhibition effect on the catalyzed reaction of bromate and hydrazine by selenium. Using this effect, V(V) can be determined in the range of 70 to 2500 ng in 10 mL of solution. The optimization procedure includes pH and selenium concentration. An extraction method was used for interference removal. The method was applied to the determination of vanadium in petroleum. Received: 20 October 1998 / Revised: 17 April 1999 / Accepted: 3 June 1999     

Kinetic-spectrophotometric determination of Sb(V) based on its reaction with iodide in the presence of methylene blue

A rapid, simple, and sensitive kinetic method is developed for the determination of trace amounts of Sb(V). The method is based on the reaction of Sb(V) with iodide in acidic media in the presence of methylene blue. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance at 664 nm by a fixed-time technique of 60 s. The method allowed the determination of Sb(V) at concentrations between 0.01 and 2.2 μg/mL. The limit of detection was 0.006 μg/mL and the relative standard deviation for ten replicate measurements of 0.5 μg/mL Sb(V) was 1.2%. The method was applied to the determination of Sb(V) in tap water and spring water with satisfactory results. The text was submitted by the authors in English.     

Catalytic kinetic spectrophotometric determination of iron with (dibromo-<Emphasis Type="Italic">p</Emphasis>-sulfonic acid arsenazo)-potassium bromate-ascorbic acid system

A new method for the determination of traces of iron was developed based on its catalytic effect on the oxidation reaction of dibromo-p-sulfonic acid-arsenazo (DBS-arsenazo, DBS-ASA) by potassium bromate in a 5.0 × 10⁻³ M sulfuric acid medium. The optimum experimental conditions for the determination of iron using iron(III)-dibromo-p-sulfonic acid-arsenazo, (DBS-ASA)-potassium bromate-ascorbic acid system and its kinetic spectrophotometric properties were studied. The absorbance difference (ΔA) is linearly related with the concentration of iron(III) over the range of 0.20–6.0 ng/mL at the maximum absorption wavelength of 520 nm and described by the equation: ΔA = 0.133c (ng/mL) — 0.0133 with a regression coefficient of 0.9966. The detection limit of the method is 0.17 ng/mL. The method has been successfully used in the determination of traces of iron in potato samples. The obtained results agree with those of atomic absorption spectrometry.     

Determination Of SE(IV) in the Presence of SE(VI) at NG ML− Concentration Levels by a Kinetic Spectrophotometric Method

ABSTRACT

The catalytic effect of Se(IV) on the reduction reaction of thionine(TN) by sulfide ion is used for determination of trace amounts of selenium(IV) ion by a kinetic-spectrophotometric method. This new method is simple and highly sensitive. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of the reaction mixture at 598 nm. The fixed time method was used for the first 45s from initiation of the reaction. Under the optimum conditions, in the concentration range of 2-90 ng ml^? of selenium(IV), a quite linear regression equation (r = 0.9984, n = 14) was obtained. The experimental detection limit of the method (S/N = 3) was 1.3 ng ml^?. The relative standard deviation of ten replicate measurements is 2.51% for a 40 ng ml^? solution of selenium. The proposed method is used to the study of selenium (IV,VI) speciation in water at ng ml^? levels. This method was extended for the determination of selenium in real samples.     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997