Spectrophotometric determination of vanadium using variamine blue and its application to synthetic, environmental and biological samples

A simple, rapid and accurate spectrophotometric method is described for the determination of trace amounts of vanadium using variamine blue (VB) as a chromogenic reagent. The method is based on the oxidation of variamine blue to form a violetcolored species on reaction with vanadium(V), having an absorption maximum at 570 nm. Beer’s law is obeyed in the range of 0.1–2.0 μg ml^?1. The molar absorptivity and Sandell’s sensitivity were found to be 1.65 × 10⁴ l mol^?1 cm^?1 and 0.003 μg cm^?2, respectively. Optimum reaction conditions were evaluated in order to delimit the linear range. The effect of interfering ions on the determination is described. The proposed method has been successfully applied to the determination of vanadium in steel, pharmaceutical, environmental, and biological samples.     

Titrimetric determination of uranium (IV) with iron (III) using redox indicators

Summary Conditions have been established for the use of methylene blue, thionine and variamine blue as redox indicators in the titrimetric determination of uranium(IV) with iron(III) in an inert atmosphere at 98–100° C. Under the conditions prescribed, the method gives results with an accuracy of ±0.4%. The advantages of this method are discussed for the determination of uranium(IV) in the presence of iron(II).Methylene blue and thionine are more satisfactory than variamine blue, because variamine blue is not sufficiently stable at the necessary temperature, especially in hydrochloric acid medium.

---

Zusammenfassung Die volumetrische Bestimmung von Uran(IV) mit Eisen(III) kann mit Hilfe von Methylenblau, Thionin oder Variaminblau als Redox-indicatoren in inerter Atmosphäre bei 98–100° C durchgeführt werden. Das Verfahren liefert unter den beschriebenen Bedingungen auf ±0,4% genaue Ergebnisse und ist besonders vorteilhaft für die Uran(IV)-be-stimmung in Gegenwart von Eisen(II). Variaminblau ist ungünstiger als die beiden anderen Indicatoren, da es bei der erforderlichen Tem-peratur nicht genügend stabil ist, besonders in salzsaurem Medium.

     

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.     

Quantitative and qualitative studies of silica in different rice samples grown in north of Iran using UV-vis, XRD and IR spectroscopy techniques

Silicon is an essential trace element and is found in vegetables, fruits, cereals, water, pasta and rice (Oryza sativa). In this work, the silica content of different types of rice grains were measured. Here, we used the heteropoly blue photometric method with a double beam UV-vis spectrophotometer to determine the amount of silicon in rice samples (n = 7) that were collected in the north of Iran. The samples were digested with wet-ashing method by microwave-assisted heating and then treated with ammonium molybdate to produce a yellow color compound in acidic solution (ca. pH 1.2) and then reduced to give a heteropoly compound with a blue color. Analyses were performed using standard addition method and absorbance values were measured with double beam UV-vis spectrophotometer at λ_max = 815 nm. Results indicated that the silica content was 307-451 mg/kg for the samples. X-ray diffraction patterns and infra-red spectra were obtained from rice samples without any sample treatment.     

Spectrophotometric determination of selenium(IV) with 4-methyl-<Emphasis Type="Italic">o</Emphasis>-phenylenediamine based on piazselenol formation

A method has been developed for the spectrophotometric determination of selenium(IV) using 4-methyl-o-phenylenediamine (MOPDA) as a chromogenic reagent. In hydrochloric acid media at about pH 2, MOPDA forms a piazselenol complex with selenium(IV), which gives an absorption maximum at 332 nm. After transfer of the formed piazselenol complex into organic phase with n-hexane, the absorbance of the piazselenol complex was measured by a UV-Vis spectrophotometer. The effective parameters of the experimental conditions such as pH, formation time of the complex, amount of MOPDA, ionic strength, volume of sample and effects of diverse ions, were investigated. The detection limit of the proposed method was found to be 0.95 μg/L Se(IV) (n = 14, 3σ). The method was successfully applied to tap water, sea water and wastewater samples from washings of flue gases with satisfactory results.     

Evaluation of ammonia as diluent for serum sample preparation and determination of selenium by graphite furnace atomic absorption spectrometry

A method for the determination of total selenium in serum samples by graphite furnace atomic absorption spectrometry was evaluated. The method involved direct introduction of 1:5 diluted serum samples (1% v/v NH₄OH+0.05% w/v Triton X-100^®) into transversely heated graphite tubes, and the use of 10 μg Pd+3 μg Mg(NO₃)₂ as chemical modifier. Optimization of the modifier mass and the atomization temperature was conducted by simultaneously varying such parameters and evaluating both the integrated absorbance and the peak height/peak area ratio. The latter allowed the selection of compromise conditions rendering good sensitivity and adequate analyte peak profiles. A characteristic mass of 49 pg and a detection limit (3s) of 6 μg 1⁻¹ Se, corresponding to 30 μg l⁻¹ Se in the serum sample, were obtained. The analyte addition technique was used for calibration. The accuracy was assessed by the determination of total selenium in Seronorm™ Trace Elements Serum Batch 116 (Nycomed Pharma AS). The method was applied for the determination of total selenium in ten serum samples taken from individuals with no known physical affection. The selenium concentration ranged between 79 and 147 μg l⁻¹, with a mean value of 114±22 μg l⁻¹.     

阴极溶出催化极谱法测定微量硒

本文提出将溶出伏安法和极谱催化法结合起来,用溶出催化波来测定微量硒;考察了各种试验条件及其它离子对分析结果的影响,并对实样进行了分析测定。用国产883型笔录式极谱仪,配用旋转玻碳电极测定硒,电解富集3-5分钟,可定量测定浓度在4×10^-9-1×10^-7M 范围内的硒;富集20-30分钟,硒的检出下限为7×10^-10M。测定时不必除氧。在测定硒的基础上,用玻碳电极和大汞电极相配合,对硒的溶出催化电极过程进行了研究,探讨了此过程中各步反应的机理。     

Determination of Selenium in Natural Waters Using the Centrifugal Photometric Analyzer

Abstract

A rapid ion exchange separation converts the methylene blue spot test for selenium into a selective and sensitive method for quantitative determination of trace quantities of selenium. Increased speed, accuracy, and reproducibility is achieved because of the parallel analysis technique of the centrifugal photometric analyzer (GeMSAEC Fast Analyzer). Natural water samples, spiked with 0.10 to 0.5 μg of selenium, were analyzed with an average accuracy of 4.2 % after removal of interferences by ion exchange.     

g-C3 N4 富集结合毛细管电泳与电感耦合等离子体质谱联用分析西瓜中硒形态

硒是人体所必需的微量元素之一,对人身体健康非常重要。该工作称取2.0 g三聚氰胺于反应釜中,在600℃下密闭加热2 h,冷却至室温,取0.5 g上述产物置于烧杯中在室温下超声10 h,静置30 min,取上层乳白色溶液于60℃下烘干,即得类石墨烯氮化碳（g-C₃ N₄ ）。所制备的g-C₃ N₄ 经傅里叶变换红外光谱（FT-IR）、X射线粉末衍射（XRD）、场发射环境扫描电子显微镜（SEM）进行表征,证明g-C₃ N₄ 已经成功合成。建立了毛细管电泳-电感耦合等离子体质谱（CE-ICP-MS）联用技术测定西瓜中硒形态的新方法。用胃蛋白酶作提取剂及超声波辅助提取西瓜中的硒形态,经g-C₃ N₄ 富集、长100 cm内径100 μm毛细管分离,电泳电压为22 kV,缓冲液为8 mmol/L NaH₂ PO₄ -12 mmol/L H₃ BO₃ -0.2 mmol/L十六烷基三甲基溴化铵（CTAB）（pH 9.2）,于11 min内完全分离6种硒形态。所建立的方法检测速度快、灵敏度高,采用CH₄ 作动态反应气消除干扰。硒脲（SeUr）、硒代胱氨酸（SeCys₂ ）、硒代蛋氨酸（SeMet）、亚硒酸钠（Se（Ⅳ））、硒酸钠（Se（Ⅵ））、硒代乙硫氨酸（SeEt）的线性范围（按Se计）分别为0.017~20 μg/L、0.091~50 μg/L、0.032~40 μg/L、0.023~60 μg/L、0.015~75 μg/L、0.015~30 μg/L。各硒形态的线性相关系数均大于0.9995,SeUr、SeCys₂ 、SeMet、Se（Ⅳ）、Se（Ⅵ）、SeEt的检出限分别为6.2、30、11、8.2、48、5.5 ng/L,回收率为96.0%~106%,RSD < 3%。将本方法应用于西瓜中硒形态分析,结果令人满意。     

Self-diffusion coefficient of water in Nafion-117 membrane with different monovalent counterions: a radiotracer study

The self-diffusion coefficient of water in Nafion-117 membrane in different cationic forms was measured by the transient radiotracer method, which is based on an analytical solution of Fick's second law. The self-diffusion coefficient of water in the membrane was obtained from the analysis of time-dependent isotopic-exchange rates of tritium tagged water between sample of Nafion-117 membrane and equilibrating water. This transient method does not require the knowledge of partition coefficient of water, which is an essential parameter in the radiotracer permeation method. In present work, self-diffusion coefficients of water in the Nafion-117 membrane with H⁺, Li⁺, Ag⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ monovalent counterions were obtained. The values of logarithm of self-diffusion coefficients were found to vary linearly as a function of polymer volume fraction except for membrane sample with H⁺ counterions. The self-diffusion coefficient of water in Nafion-117 membrane with H⁺ counterions was significantly different from the trend observed in the variation of self-diffusion coefficient of water as a function of polymer volume fraction in the membrane with other monovalent counterions. This observation seems to suggest that the physical structure of Nafion-117 membrane in H⁺ form may be quite different from the Nafion-117 membrane with other monovalent counterions. The high self-diffusion coefficient of water (1.67 × 10⁻⁶ cm²/s) in Nafion-117 membrane with Cs⁺ counterions indicates that the ionic clusters in Nafion-117 membrane are well connected even at low water content (8.2 wt.%) in the membrane.     

Speciation analysis of arsenic and selenium compounds in environmental and biological samples by ion chromatography-inductively coupled plasma dynamic reaction cell mass spectrometer

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic (IC) detector for the speciation analysis of arsenic and selenium. The arsenic and selenium species studied included arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), selenite [Se(IV)] and selenate [Se(VI)]. Gradient elution using (NH₄)₂CO₃ and methanol at pH 9 allowed the chromatographic separation of all species in less than 12 min. Effluents from the IC column were delivered to the nebulization system of ICP-DRC-MS for the determination of arsenic and selenium. The potentially interfering ³⁸Ar⁴⁰Ar⁺ and ⁴⁰Ar⁴⁰Ar⁺ at the selenium masses m/z 78 and 80 were reduced in intensity by approximately 3 orders of magnitude by using 0.6 mL min⁻¹ CH₄ as reactive cell gas in the DRC while an Rpq value of 0.3 was used. Meanwhile, arsenic was determined as the adduct ion ⁷⁵As¹²CHH⁺ at m/z 89, which is more sensitive than ⁷⁵As. The limits of detection for arsenic and selenium were in the range of 0.002–0.01 ng mL⁻¹ and 0.01–0.02 ng mL⁻¹, respectively, based on peak height. The relative standard deviation of the peak areas for five injections of 5 ng mL⁻¹ As and Se mixture was in the range of 2–4%. The concentrations of arsenic and selenium species have been determined in urine samples collected locally. The major As and Se species in urines were AsB, DMA and probably selenosugar at concentration of 20–40, 15–19 and 17–31 ng mL⁻¹, respectively. The recoveries were in the range of 94–105% for all the determinations. This method has also been applied to determine various arsenic compounds in two fish samples. In this study, a simple and rapid microwave-assisted extraction method was used for the extraction of arsenic compounds from fish. The arsenic species were quantitatively leached with an 80% v/v methanol solution in a focused microwave field during a period of 5 min.     

Evaluation of an on-line coupled continuous flow liquid membrane extraction and precolumn system as trace enrichment technique by liquid chromatographic determination of bisphenol A

An on-line coupled continuous flow liquid membrane extraction (CFLME) and C₁₈ precolumn system was developed for sample preconcentration in liquid chromatography determination. After preconcentration by CFLME, which is based on the combination of continuous flow liquid–liquid extraction and supported liquid membrane, bisphenol A (BPA) was enriched in 960 μl of 1 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto a C₁₈ analytical column for separation and detected at 220 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor, and enrichment time were optimized. The proposed method presents a detection limit of 0.03 μg l⁻¹ (S/N=3) when 60 ml samples was enriched with an enrichment time of 30 min. Compared with C₁₈ based column-switching procedure, this proposed procedure presents similar sample throughput and lower detection limits. The proposed method was successfully applied to determine BPA in tap water, river water, and municipal sewage effluent samples.     

A novel method for the preparation of Bi4Ti3O12 nanoparticles in w/o microemulsion

Nanometer-sized Bi₄Ti₃O₁₂ particles have been prepared by chemical reaction of bismuth nitrate pentahydrate, titanium sulfate and ammonia solution in a reverse microemulsion system consisting of water, OP (P-octyl polyethylene glycol phenylether, non-ionic surfactant), n-butanol (co-surfactant), and cyclohexane (oil). Precursor hydroxides precipitated in the droplets of water-in-oil (w/o) microemulsion were calcined at 800 °C for 4 h to form Bi₄Ti₃O₁₂ nanoparticles. The samples were investigated with X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectrophotometer (FT-IR) and ultraviolet visible spectrophotometer (UV–vis). It was found that the as-prepared Bi₄Ti₃O₁₂ nanoparticles had small particle sizes (35 nm), high crystallinity, narrow size distributions and strong light absorption properties not only in the ultraviolet light but also in the visible light region.     

Stability of selenium and its speciation analysis in water using automatic system separation and HR-ICP-MS measurement

A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) measurement. ⁷⁵Se(IV) and ⁷⁵Se(VI) were prepared and used as tracers during the experiments. The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure. The parameters which affect the uptake of Se(IV) and Se(VI) on Dowex1 × 8 resin was optimized and the procedure for Se(IV) and Se(VI) separation was proposed. Both Se(IV) and Se(VI) are retained on the column in natural or alkaline solution with high distribution coefficient. The successive gradient elution of pre-concentrated species of selenium with HNO₃ solution allows to differentiate between them. Se(IV) and Se(VI) finally were eluted with 0.05 mol/L HNO₃ and 5.0 mol/L HNO₃, respectively. The proposed method has been successfully verified using the certified reference materials (CRMs) of real water samples, and spiked recoveries for real samples were 98%-104% with 5% relative standard deviations (RSDs). The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.     

Application of potassium ferricyanide in the spectrophotometric determination of captopril

A novel method for the determination of captopril by speetrophotometer is described in this paper. The experiment is based on the fact that Fe(Ⅲ) is reduced to Fe(Ⅱ) by captopril, then the in situ formed Fe(Ⅱ) reacts with potassium ferricyanide to give the soluble prussian blue at pH 4.00, and its maximal adsorption wavelength (λmax) is 735 nm. Good linear relationship is obtained between the absorbance and the concentration of captopril in the wide range of 0.05-20 μg/mL. The linear regression equation is A = -0.04314 + 0.11423C (μg/mL) with a correlation coefficient R = 0.9998. The detection limit (3a/k) is 0.04 μg/mL, the molar absorption coefficient is 2.5×104 L/mol cm. By mensurating the absorbance of soluble prussian blue, the indirect determination of eaptopril can be obtained. This method has been successfully applied to determination of captopril in pharmaceutical samples.Analytical results obtained are satisfactory.     

Sensing of Trace Amounts of Dodecyl Benzene Sulfonate by Solid Phase Spectrophotometry

A very simple, selective and sensitive spectrophotometric method for the determination of dodecyl benzene sulfonate (DBS) has been investigated. In this method, the ion pair of DBS and methylene blue was adsorbed onto plasticized poly(vinylchloride) membrane as a solid phase extraction medium. The absorbance of the blue membrane was measured at 660nm against a blank membrane using a spectrophotometer. The influence of type and amount of plasticizer, pH, concentration of methylene blue, temperature of sample solution and time of extraction on the absorbance of membrane was studied. Linear calibration was obtained over a concentration range of 0.1 to 6.5µgmL^–1 of DBS. The method was applied to the determination of DBS in different commercial detergents. The precision and accuracy of the method is comparable with the conventional standard method. This method is cost-effective, and the use of organic solvent such as chloroform is completely eliminated.     

Direct electrothermal atomic absorption spectrometric determination of selenium in serum

The effect of copper, iron, nickel and silver ions on the thermal stability of inorganic and metabolized forms of selenium in serum was studied with radioactive ⁷⁵Se. Copper and iron had no stabilizing effect but in the presence of nickel or silver the temperature could be raised to 1050°C or 1250°C, respectively, without loss of selenium. On this basis an electrothermal atomic absorption spectrometric method was developed for the direct determination of selenium in human serum; selenium is stabilized with nickel during ashing. In 12 samples of sera from unexposed individuals, the concentrations ranged from 92 pob to 140 ppb. The relative standard deviation of the method is 4%, and the detection limit is 5 ppb.     

An automated submicrogram determination of selenium in vegetation by quartz-tube furnace atomic-absorption spectrophotometry

An automated method for the determination of submicrogram amounts of selenium in vegetation is described. A weighed sample of vegetation is digested with a 4:1 nitric-perchloric acid mixture, and made up to a known volume. The digested sample is placed in a Technicon sampler and reacted with sodium borohydride solution. The selenium converted into the gaseous hydride is swept by an argon stream into a gas-liquid separator. The mixed gas stream is passed through a heated quartz cell, positioned in the light-path of an atomic-absorption spectrophotometer. The absorption by the atomized selenium is recorded. The method is capable of analysing 50 samples a day by the use of a calibration curve or 25 a day by the standard addition technique. A relative standard deviation of better than 10% and a detection limit of 0.025 microg/g were obtained.     

Molecular iodine preconcentration and determination in aqueous samples using poly(vinylpyrrolidone) containing membranes

Membranes for preconcentration of molecular iodine were developed by two different routes: (i) UV-grafting of 1-vinyl-2-pyrrolidone in the pores of microporous poly(propylene) host membrane (grafted membrane), and (ii) physical immobilization of preformed poly(vinylpyrrolidone) (PVP) in a plasticized cellulose triacetate matrix to form the polymer inclusion membrane (PVP-PIM). The UV-grafted PVP-membrane was found to be hydrophilic (water uptake capacity = 166 wt.%), while the PVP-PIM was found to be highly hydrophobic (≈2 wt.%). PVP-PIM was found to uptake only I₂ from aqueous sample whereas I₂ and I₃⁻ were sorbed in the grafted membrane. This selectivity of PVP-PIM towards I₂ was attributed to its hydrophobicity that allows only neutral I₂ to interact with PVP in the membrane matrix. Thus, the selective preconcentration and quantitative determination of I₂ in aqueous sample was carried out using PVP-PIM. As PVP-PIM was optically transparent, the characteristic absorbance of PVP–I₂ complex (λ_max = 361 nm) could be used for quantitative determination of I₂ in the membrane. The instrumental neutron activation analysis (INAA) of the I₂-loaded PIM samples indicated that 82% could be sorbed into the PIM samples from the solution within 10 min of equilibration time. This membrane was applied to I₂ determinations in the samples of ¹³¹I radiotracer. The concentration level of iodine species in these samples were in sub-ppb level. Therefore, these samples were ideal for testing the preconcentration efficiency of the membrane towards I₂ by monitoring the radioactivity of ¹³¹I. The amounts of I₂ in the aqueous samples were standardized by conventional solvent extraction of I₂ with the chloroform for validating the preconcentration efficiency of PVP-PIM. The detection limit of I₂ in aqueous samples by INAA hyphenated with PVP-PIM was found to be 0.3 ppb for a sample size of 25 mL.     

Nafion-PAN optical chemical sensor: optimization by FIA

A copper-sensitive optical chemical sensor (optrode) is described. The optrode is based on a Nafion membrane and an immobilized organic ligand coupled with a flow injection (FI) system. The FI system includes a flow-through removable measuring cell and a simple spectrophotometer. Owing to the miniature size of the system and the efficient use of optical fibers, this optrode is well suited for monitoring environmental water samples. The success of the described optrode system depends on the effectiveness of the FI reagent delivery system. Optimum contact time with the membrane (as determined by the reagent flow rates) and the injected sample volume are critical. Environmental water samples were analyzed for copper content using the optimized optrode system. To validate the optrode's performance, the same water samples were analyzed using the atomic absorption spectrophotometer.