Spectrophotometric determination of selenium by use of thionin

A simple, rapid, and sensitive spectrophotometric method has been developed for the determination of selenium in real samples of water, soil, plant materials, human hair, and synthetic cosmetic and in pharmaceutical preparations. The method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine. The liberated iodine bleaches the violet color of thionin, and which is measured at 600 nm. This decrease in absorbance is directly proportional to selenium concentration and obeys Beer's law in the range 1-5 micro g selenium in a final volume of 10 mL (0.1-0.5 microg mL(-1)). The molar absorptivity and Sandell's sensitivity of the method were found to be 7.33 x 10(4) L mol(-1) cm(-1) and 0.0011 microg cm(-2), respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described.     

A new reagent system for the highly sensitive spectrophotometric determination of selenium

Highly sensitive and simple spectrophotometric determination of selenium is described for the determination of selenium(IV) using a new reagent leuco malachite green. The method is based on the reaction of selenium(IV) with potassium iodide in an acidic condition to liberate iodine, the liberated iodine oxidizes leuco malachite green to malachite green dye. The green coloration was developed in an acetate buffer (pH 4.2–4.9) on heating in a water bath (∼ 40 °C). The formed dye exhibits an absorption maximum at 615 nm. The method obeys Beer’s law over a concentration range of 0.04–0.4 μg mL⁻¹ selenium. The molar absorptivity and Sandell’s sensitivity of the color system were found to be 1.67 × 10⁵ L mol⁻¹ cm-¹ and 0.5 ng cm⁻², respectively. The optimum reaction conditions and other analytical parameters have been evaluated. The proposed procedure has been successfully applied to the determination of selenium in real samples of water, soil, plant material, human hair, and cosmetic samples. The results were compared to those obtained with the reference method. Statistical analysis of the results confirms the precision and accuracy of the proposed method. In addition, the developed method is cost-effective and involves easily accessible instrumentation technique which can be used by ordinary research laboratories.     

Kinetic determination of trace levels of selenium(IV) and total selenium by Nile Blue A/hydrogen peroxide method

A kinetic method for the determination of selenium(IV) traces is proposed, based on its inhibitory action on the oxidation of Nile Blue A by hydrogen peroxide in phosphate buffer (pH 10.5). A linear dependence was established between the rate of the proposed indicator reaction and selenium concentration in the range 9.5 × 10^–2-1.58 ng cm^–3. The experimental conditions of maximal selenium effect were established. Selenium, determined by the tangent method, was determined at concentrations over the range 0.22–1.26 ng cm^–3, with relative standard deviations up to 4.5%. The reaction rate was followed spectrophotometrically. The effect of foreign ions on the accuracy of this method was also investigated. The method was applied to the determination of selenium in pharmaceutical preparations and wheat flour.     

A Simple Sensitive Spectrophotometric Method for the Determination of Ce4+ Using Variamine Blue as a Chromogenic Reagent

A rapid and sensitive spectrophotometric method is described for the determination of trace amounts of cerium using Variamine Blue (VB) as a chromogenic reagent. The proposed method is based on the reaction of cerium with potassium iodide in acidic medium to liberate iodine, which oxidizes Variamine Blue to give a violet colored species with an absorption maximum at 560nm. Beers law was obeyed in the range 2–10µg mL^–1 of cerium. The molar absorptivity and Sandells sensitivity are found to be 1.65×10⁴L mol^–1cm^–1 and 8.48×10^–3µgcm^–2, respectively. The proposed method has been successfully applied to the determination of cerium in alloy and synthetic mixtures.     

溴酚蓝分光光度法测定盐酸西布曲明

在pH 3.70的B-R缓冲溶液中,盐酸西布曲明与溴酚蓝以摩尔比1比2反应形成具有正吸收和负吸收的离子缔合物,最大正吸收波长为436nm,最大负吸收波长为590nm,线性范围分别在3.4×10-6 mol·L-1(正吸收)、3.8×10-6 mol·L-1(负吸收)以内,表观摩尔吸光率为1.83×105L.mol-1.cm-1(正吸收)、5.51×104L.mol-1.cm-1(负吸收),据此建立了测定盐酸西布曲明含量的分光光度法。方法用于合成样品及尿样中盐酸西布曲明的测定,回收率在96.8%～102.5%,相对标准偏差(n=6)在0.9%～1.7%之间。     

Dosage par spectrophotométrie d'absorption atomique sans flamme de traces de sélénium après extraction à l'aide de 4-chloro-1,2-diaminobenz̀ application aux milieux biologiques

The determination of traces of selenium after extraction with 4-chloro-1,2-diaminobenzene by graphite-furnace atomic absorption spectrometry, Application, to biological samples.A new method for the determination of very small amounts of selenium by flameless atomic absorption spectrometry is proposed. The procedure was checked with aqueous solutions of selenium and applied to mineralized biological fluids (red cells and plasma). Selenium(IV) is quantitatively extracted with toluene after reaction with 4-chloro-l,2-diaminobenzene. The sample detection limit for selenium is 10 ng ml^-1. Precision and reproducibility are excellent.     

Determination of trace amounts of copper(II) by using catalytic redox reaction between methylene blue and ascorbic acid.

A sensitive and selective kinetic-spectrophotometric method is proposed for the determination of microg mL(-1) amounts of Cu2+ based on its catalytic effect on the oxidation of L-ascorbic acid by Methylene Blue in a strongly acidic medium. The reaction is monitored spectrophotometrically by measuring the decrease in color intensity of Methylene Blue at 665 nm. The analysis of Cu2+ ion is performed by a fixed-time method. At a given time of 2 min at pH 2.20 and 32 degrees C, the detection limit is 10 ng mL(-1) and the relative standard deviation for 0.4 microg mL(-1) Cu2+ is 3.60% (n = 6). The method is free from most of the interferences and the effect of diverse ions on the determination of Cu2+ is also reported. The proposed method is virtually specific to copper and has been satisfactorily applied to its determination in electric copper wire samples and pharmaceutical products. Results were also verified by the atomic absorption spectrometry technique (AAS).     

Variamine blue as a gravimetric reagent Determination of tungsten

Tungsten can be precipitated by a solution of Variamine Blue at pH 5. The precipitate is ignited to constant weight at a temperature above 600 degrees and weighed as tungsten trioxide. The method can be used for the determination of tungsten in alloy steels.     

Spectrophotometric determination of acetone using vanillin

A sensitive method is described for the spectrophotometric determination of acetone in water. Acetone reacts with vanillin in alkaline medium forming a yellow-orange dye with an absorption maximum at 430 nm. Beer's law is obeyed in the range from 0.5 to 5 p.p.m. of acetone in water. Molar absorptivity and Sandell's sensitivity were found to be 11.0 x 10(3) +/- 100 l mol-1 cm-1 and 0.005 micrograms cm-2, respectively. The important parameters for complete colour development were optimised and the method was used for the determination of acetone in biological samples. The method was also applied successfully to the determination of acetone in air after absorption in sodium hydrogen sulphite solution.     

Colorimetric Determination of Seleniumin Various Environmental Samples

A new reagent system using rhodamine‐B dye for the determination of selenium is described. The method is based on the reaction of selenium with acidified potassium iodide to liberate iodine. The liberated iodine bleaches the pink colour rhodamine‐B, which is measured at 555 nm. Beer's law is obeyed over the concentration range of 1–10 μg of selenium final solution volume of 25 mL (0.04–0.4 ppm) and the apparent molar absorptivity and Sandell's sensitivity was found to be 1.96× 10⁵ l mol^?1 cm^?1 and 0.0004 μg cm^?2, respectively. The method is simple, sensitive, and selective and is satisfactorily applied to micro‐level determination of selenium in various environmental and cosmetic samples.     

血红蛋白作为过氧化物模拟酶催化显色体系的研究与应用

研究了以血红蛋白（Ｈｅｍｏｇｌｏｂｉｎ,Ｈｂ）作为过氧化物模拟酶对过氧化氢－４－氨基安替比林（４－Ａｍｉｎｏａｎｔｉｐｙｒｉｎｅ,４－ＡＡＰ）氯取代苯酚衍生物显色体系的催化反应性能,探讨了不同氯取代苯酚类衍生物作为酶催化反应氢供体底物的构效关系及酶催化反应的可能机理。拟定了Ｈｂ催化Ｈ２Ｏ２氧化４－ＡＡＰ－２,３,个三氯苯酚（２,３,４－Ｔｒｉｃｈｌｏｒｏｐｈｅｎｏｌ,ＴＣＰ）显色体系用于Ｈ２Ｏ２的测定方法。该方法测定Ｈ２Ｏ２灵敏度高,表观摩尔吸光系数为 ２．２１×１０４ Ｌ·ｍｏｌ－１·ｃｍ－１。将拟定方法与葡萄糖氧化酶催化反应偶联,用于人血清样品中葡萄糖含量的测定,得到满意的结果。     

A rapid method for peroxide value determination in edible oils based on flow analysis with Fourier transform infrared spectroscopic detection

The development of an automated, rapid and highly precise method for determination of the peroxide value in edible oils based on a continuous flow system and Fourier transform infrared (FTIR) spectroscopic detection is described. The sample stream was mixed with a solvent mixture consisting of 25% (v/v) toluene in hexanol which contained triphenylphosphine (TPP). The hydroperoxides present in the sample reacted stoichiometrically with TPP to give triphenylphosphine oxide (TPPO) which has a characteristic and intense absorption band at 542 cm-1. A 10% (m/v) TPP solution in the solvent mixture and a 100 cm reaction coil were necessary for complete reaction. FTIR transmission spectra were recorded using a flow cell equipped with CsI windows having an optical pathlength of 100 microns. By using tert-butyl hydroperoxide spiked oil standards and evaluation of the band formed at 542 cm-1 a linear calibration graph covering the range 1-100 PV (peroxide value; mequiv O2 kg-1 oil) was obtained. The relative standard deviation was 0.23% (n = 11) and the throughput 24 samples h-1. The developed system was also applied to the determination of PV in olive, sunflower and corn oils, showing good agreement with the official reference method of the European Community which is based on titration using organic solvents. The results obtained clearly show that the developed method is superior to the standard wet chemical method, hence suggesting its application in routine analysis and quality control.     

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.     

Flow injection spectrophotometric determination of trace amounts of selenium

A simple, rapid and sensitive flow injection spectrophotometric method for determination of selenium (0.005-1.5 mug ml(-1)) is described. The method is based on the catalytic effect of Se(IV) on the reduction reaction of thionine (TN) with sulphide ion, monitored spectrophotometrically at 598 nm. The detection limit is 5 ng ml(-1) the relative standard deviation for eight replicate measurements is 1.1% for 1 mug ml(-1) of selenium. The sampling rate is 25-30 samples h(-1). The procedure was applied successfully to the determination of selenium in real samples.     

Flow-injection simultaneous determination of selenium(IV) and selenium(IV + VI) using photooxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A flow-injection spectrophotometric method has been developed for the simultaneous determination of selenium(IV) and (IV + VI) at nanogram per milliliter levels. It is based on the catalytic effect of selenium(IV) on the photooxidative coupling of p-hydrazinobenzenesulfonic acid (HBS) with N-(1-naphthyl)ethylenediamine (NED) to form an azo dye (λ_max = 538 nm). In this reaction, bromide acted as an activator for the catalysis of selenium(IV) and an reducer for selenium(VI) to selenium(IV) in an acidic medium which allowed the determination of selenium(IV + VI). A sample solution, being split by Y-piece into two portions, passed through the low-temperature coil (4 m, 25 °C) and the high-temperature coil (20 m, 100 °C). By monitoring the absorbance of the dye produced in the two portions, selenium(IV) and (IV + VI) in the range of 0.2–6 ng ml⁻¹ were determined simultaneously. The relative standard deviations for 3 ng ml⁻¹ selenium(IV) and (VI) (n = 10) were 1.2 and 1.3%, respectively. There were few interfering ions in the selenium determination. The proposed method was applied to the determination of selenium(IV) and (VI) in natural water samples.     

Spectrophotometric determination of trace amounts of selenium with catalytic reduction of bromate by hydrazine in hydrochloric acid media

A method is presented for the determination of selenium, based on the catalytic effect of selenium(IV) on the reduction reaction of BrO(-)(3) by N(2)H(4).2HCl. The decolourization of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. This method is precise, highly sensitive, simple, rapid, widely applicable and selective for the determination of selenium(IV) and total selenium. The variables which affected the reaction rate were fully investigated and the optimum conditions were established. Selenium, as low as 1 ng/ml, can be determined by this method. The relative standard deviation of 20 ng of selenium was 0.94% (N = 10). The method was applied to the determination of Se(IV) in a health-care product.     

New Indicator Reactions Involving Sulfur-Containing Organic Compounds for the Kinetic Determination of Selenium

New indicator reactions were proposed for the determination of selenium by the kinetic method based on the reduction of Methylene Blue by some sulfur-containing organic compounds. It was demonstrated that a high sensitivity of the determination of selenium is attained using unithiol and thiomalic, 2,3-dithiomercaptopropionic, and rubeanic acids as reducing agents. In the presence of unithiol, down to 4 ng/mL selenium can be determined.     

Chelatometrische bestimmung von zink-, cadmium- und bleiionen in anwesenheit von variaminblau als redoxindikator

A direct chelatometric method for the determination of zinc, cadmium and lead ions was developed. Using the redox systems potassium ferrocyanide-potassium ferricyanide and Variamine Blue as redox indicator, the determination could be carried out at pH 5 with sufficient accuracy Magnesium, barium, strontium and calcium do not disturb the determination. In solutions containing zinc, lead or cadmium ions, magnesium can also be determined when Eriochrome Black T is used as the indicator.     

Protonation and second step of oxidation of variamine blue: Quantum-chemical treatment

It has been shown by MNDO, AM 1, and PM3 calculations that, of the two possible conjugated acids of 4-amino-4′-methoxydiphenylamine (Varianime Blue), the form protonated via the primary amino group is oxidized first. The cation protonated via the primary amino group is more favorable energetically if hydration is taken into account. The detailed mechanism of the second step of oxidation of Variamine Blue was estimated based on the results of INDO, MNDO, AMI, and PM3 calculations (UHF formalism) of the charge distribution and spin density in the Variamine Blue radical cation.     

Highly selective flow injection spectrophotometric determination of gold based on its catalytic effect on the oxidation of variamine blue by potassium iodate in aqueous N,N-dimethylformamide medium

A highly selective and simple flow injection method is reported for the determination of Au(III) in jewel samples. The method is based on the catalytic effect of Au(III) on the oxidation of 4-amino-4′-methoxydiphenylamine hydrochloride (Variamine Blue B base, VB) by KIO₃. The colored reaction product was monitored spectrophotometrically at 546 nm. A volume fraction of 40% N,N-dimethylformamide (DMF) greatly enhances the selectivity of the method. The chemical (pH and concentrations of reagents) and instrumental variables (sample injection volume, reagents flow rates, reaction coil length) affecting the determination were studied and optimized. Under the selected values, the analyte could be determined in the range of 0.1-12.0 mg L⁻¹ (r = 0.9997), at a sampling rate of 120 h⁻¹. The proposed assay was precise (s_r = 0.8% at 5.0 mg L⁻¹ Au(III), n = 12) and adequately sensitive with a 3σ limit of detection of 0.03 mg L⁻¹. The method was successfully applied to the analysis of jewel samples. The obtained results were favorably compared to flame atomic absorption spectrometry (FAAS) used as a reference method.