Mixed micellar medium for the spectrophotometric determination of molybdenum in molybdenum/tungsten mixtures

Effects of cetyltrimethylammonium bromide (CTAB) and/or nonylphenoxypolyethoxyethanol (OP) on the absorption spectra of the complexes of molybdenum and tungsten with bromopyrogallol red (BPR) were studied. Based on these effects, a mixture of CTAB and OP was thus selected as a medium for the selective and sensitive determination of Mo in Mo/W binary mixtures. Under the optimum conditions, Beer's law was obeyed over the range 0.06-0.8 mug ml(-1) Mo with molar absorptivity being 1.3x10(5) l mol(-1) cm(-1) and detection limit 0.025 mug ml(-1). For 1.0 mug Mo, at least 20 mug W did not interfere in the determination of Mo with average recovery and relative standard deviation being 99.5% and <2%, respectively. The method developed maintained the features of simplicity and rapidity and, moreover, its selectivity and sensitivity enhanced greatly due to the use of CTAB/OP mixed micellar medium. When coupled with a compatible concentration method, the proposed method could be used for the determination of trace Mo in natural waters.     

Electroreduction of molybdenum(VI) at a prehydrogenated platinum electrode

The use of hydrogenated platinum electrodes allows observation of the electroreduction of some oxygenated ions, which is otherwise masked by the reduction of the hydrogen ion. The present paper deals with the reduction of molybdenum(VI) at a prehydrogenated platinum electrode in acid solutions. The experimental conditions for the electrode hydrogenation process are the following: 90 min at a cathodic current density of about 7 A/cm(2) for microelectrodes with an area of 0.02-0.03 cm(2); about 120 min at a current density of 1.5-2 A/cm(2) for microelectrodes with an area of 0.25-0.35 cm(2). The reduction of molybdenum(VI) in 0.8-1.6M H(2)SO(4) occurs in two consecutive steps: the more cathodic wave [Mo(V) to Mo(III)] is for the most part masked by the reduction of the solvent; the less cathodic wave [Mo(VI) to Mo(V)] takes place at E(1 2 ) values of about +0.07 V, is well shaped, diffusion-controlled and usable for the determination of molybdenum down to 4 x 10(-5)M or 6 x 10(-5)M if a rotating disk electrode is used. Interferences from diverse ions have been studied. A generalization of the effect of electrode hydrogenation on the reduction of those oxygenated ions so far studied [i.e., vanadium(IV), uranium(VI) and molybdenum(VI)] is presented.     

Spectrochemical cobalt,molybdenum and copper determinations in plants

This paper deals with the spectrochemical determination of some trace elements (Cu, Mo and Co), especially in plant samples. Data are given about the choice of light source and spectral apparatus, as well as detailed remarks concerning the optical arrangement.In the concentrating pretreatment with precipitating chemicals a wet ashing has been proved to give better results than a dry ashing.     

Spectrophotometric and fluorometric determination of traces of molybdenum in soils and plants

The reaction of the molybdenum oxypentathiocyanate ion with the dyestuff Rhodamine B (RhB) produces the ternary complex. MoO(SCN)(5)(RhB)(2) The formation of this complex is accompanied by a colour change and by extinction of the fluorescence of RhB. A spectrophotometric and fluorometric method for the determination of Mo has been developed from these observations. The method is free from interferences and has detection limits of 0.1 mug and 0.05 mug of Mo for absorption and fluorescence measurements, respectively. The spectrophotometric method is applicable to the determination of Mo in soils and the fluorometric method is suited to the determination of Mo in plants.     

Spectrophotometric and volumetric molybdenum determination with 2,2'-biquinoxalyl

Volumetric and spectrophotometric methods for molybdenum determination based on reaction with 2,2'-biquinoxalyl (2,2'-BQx) in concentrated hydrochloric acid media have been developed. Absorption spectra of the 1,1'-dihydro 2,2'-biquinoxalylene complex shows the most intensive absorption band at 685 nm with molar absorptivity = 3.3 x 10(4) 1. mole(-1). cm(-1). The compound is characterized by good durability to high temperatures and concentrated acid media. The mentioned indicator gives distinct colour changes at the titration end-point. The spectrophotometric method for molybdenum determination is based on the use of the difference in absorbance between the oxidized and reduced forms of 2,2'-BQx. The indicator is reduced with Sn(II) and then part of it is reoxided as a result of addition of Mo(VI). The difference in absorbance between the blank determination and molybdenum sample increases linearily in the concentration range 0.2-2.0 mug Mo/cm(3). 2,2'-Biquinoxalyl was used as an indicator in the volumetric method for the determination of molybdenum concentrations in steel alloy. The interfering ions FE(III) and Cr(III) are easily eliminated as the precipitate of hydroxides. The mineral acids, hydrochloric sulphuric and perchloric acids, have been tested as reaction media.     

Trace determination of molybdenum and vanadium in natural waters by means of atomic spectroscopy (AAS, ICP-OES) after preconcentration

Conclusions Mo and V are abundant trace elements in the environment and of great significance for many organisms [1]. Their accurate and precise determination in natural waters by means of AAS and ICP-OES often requires a separation and/or a pre-concentration step. For the reliable and simple separation of Mo and V in the ng/l- to g/l-range, the co-precipitation on Cell-Fe and Cell-In can be applied with good reproducibility. By coupling with atomic spectroscopy, analytical procedures result for ultratrace determination of Mo and V, even in complex water matrices or biological fluids (e.g., urine).

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Atomspektroskopische Bestimmung (AAS, ICP-OES) von Molybdän- und Vanadium-Spuren in natürlichen Wässern nach Voranreicherung

     

Separation of rhenium from molybdenum, tungsten, vanadium, platinum metals and other elements by reduction and solvent extraction

Reduction in 1 M H(2)SO(4) with liquid zinc amalgam and extraction with isopentanol from 3M H(2)SO(4), separates rhenium from almost all the interfering elements of importance in rhenium determination. The small amounts of Mo, U, Fe and Ru still accompanying rhenium are removed by the thiocyanate-pentyl acetate or the oxine-chloroform extraction. The method is simple, rapid and of very wide applicability. It is particularly useful in the determination of rhenium in various alloys and tungsten-containing samples.     

Radiochemical neutron activation analysis for arsenic,cadmium, copper and molybdenum in biological matrices

A simple two step radiochemical separation scheme has been developed which permits the RNAA determination of As, Cd, Cu and Mo in biological matrices. The RNAA separation is applied following the INAA determination of at least 17 other elements in the same samples. Under our experimental conditions which included a four day decay period for handling and shipping from a remote reactor site, detection limits for As, Cd, Cu and Mo are 0.24, 6.6, 45 and 3.4 ng, respectively, in NBS biological standard reference materials SRM 1571 and 1567. Decontamination factors for the major spectral interferences,⁸²Br,⁴²K,²⁴Na³²P and¹²²Sb have been determined and found to be sufficiently high for measurement of the elements of interest in most biological matrices. The overall INNA/RNAA procedure takes full advantage of high resolution Ge(Li) gamma-ray spectroscopy and involves minimal chemical processing.     

Simultaneous determination of titanium and molybdenum in steel samples using derivative spectrophotometry in neutral micellar medium

A simple, selective and sensitive spectrophotometric method has been developed for the individual and simultaneous determination of Ti(IV) and Mo(VI) using resacetophenone p-hydroxybenzoylhydrazone (RAPHBH) in presence of Triton X-100, without any prior separation. Beer's law is obeyed between 0.13-1.2 microg mL-1 and 0.18-1.90 microg mL-1 concentration of Ti(IV) and Mo(VI) at 455 nm and 405 nm, respectively. The molar absorptivity and Sandell's sensitivity of the coloured complexes at pH 3.0 are 3.1x10(4) L mol-1 cm-1, 4.2x10(4) L mol-1 cm-1, and 1.6 ng cm-2, 2.3 ng cm-2 for Ti(IV) and Mo(VI), respectively. The stoichiometry of the complexes were found to be 1:2 and 1:1 (metal:ligand) for Ti(IV) and Mo(VI), respectively. These metal ions interfere with the determination of each other in zero-order spectrophotometry. The first derivative spectra of these complexes permitted a simultaneous determination of Ti(IV) and Mo(VI) at zero crossing wavelengths of 500.0 nm and 455.0 nm, respectively. The effect of foreign ions in the determination of Ti(IV) and Mo(VI) were investigated. The proposed method has been successfully applied for the determination of titanium and molybdenum in standard alloy steel, mineral and soil samples.     

Specific method for spectrophotometric determination of molybdenum in soil

A new, simple and specific spectrophotometric method for the determination of Mo in the soil extracts is described. Mo(VI) is reduced to Mo(V) with sodium borohydride and allowed to react with SCN^– ions in the presence of cationic and neutral surfactants e.g. CPC and TX-100 in the acidic aqueous solution. The molar absorptivity of the complex in both the aqueous, and toluene solutions is (2.30) × 10⁴ 1mol^–1 cm^–1 at absorption maximum, 460 nm. The extraction-procedure preconcentrated Mo at least 3-folds. the detection limit is 125ng Mo/g soil. The analytical variables of the method have been optimised and composition of the complex is proposed. None of the tested foreign ion interfered in the determination of Mo up to a large amount. An attempt for the removal of Fe-interference in the determination of Mo in soil extract has been described. The method has been found to be satisfactorily applicable for the determination of Mo in hot water leachates and acid digested soil solutions at lower ppm levels.     

APDC沉淀分离富集石墨炉原子吸收测定海水和生物样品中铅,镉,钴,铜,锡,砷和钼

我们曾研究一种新的分离富集方法,即在酸性水溶液中加入吡咯烷二硫代甲酸铵(APDC)沉淀镍后,将Ni-PDC溶于甲基异丁酮(MIBK)中,有机相直接进样石墨炉原子吸收测定尿和生物样品中痕量镍.本工作将此方法扩大应用于海水和生物样品中铅、镉、钴、铜、锡、砷和钼     

Use of long-chain alkylamines for preconcentration and determination of traces of molybdenum, tungsten and rhenium by atomic-absorption spectroscopy-II: molybdenum in soils, sediments and natural waters

Molybdenum is extracted as the thiocyanate complex with the quaternary long-chain aliphatic amine Aliquat 336 in chloroform, followed by evaporation of the solvent, dissolution in MIBK, and atomic-absorption spectroscopy. The method is simple, rapid and sensitive, with few interference problems for the determination of the Mo content of soils and sediments in the range 0.1-1.0 ppm with a relative standard deviation better than 5% when 1-g samples are used. Quantitative extraction from large volumes of aqueous solution has also been confirmed, allowing the determination of Mo in natural waters in the ppM range.     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Inductively coupled plasma mass spectrometric determination of molybdenum in urine

A method was developed for the determination of molybdenum (Mo) in human urine by direct dilution of the sample in doubly distilled water with 1% HNO3 (v/v) and inductively coupled mass spectrometry (ICP-MS). In and Y were used as internal standards. Since (98)Mo provides a higher sensitivity, it was chosen as the reference isotope. The influence of different factors, such as sample dilution, HNO3 concentration and the stability of the analyte were evaluated. The detection limit (LOD) was assessed at 0.2 microg/L Mo, while the lower limit of quantification (LOQ) was 0.6 microg/L. Recoveries ranged between 97.2 and 100.7% from solutions containing from 10 to 50 microg/L Mo. Linear calibration curves were generated from 2.1 and 52.1 microg/L with coefficients of variation (CV ) ranging from 1.62 to 3.56%. In order to establish reference values (RV) for molybdenum, the procedure presented here was used to determine Mo in the urine of a population group living in Tuscany, Italy.     

Spectrophotometric determination of molybdenum as a mixed thiocyanate-monooctyl α-anilinobenzylphosphonate complex

A sensitive method for the spectrophotometric determination of molybdenum is described. Molybdenum is reduced with ascorbic acid in hydrochloric acid solution, and complexed with thiocyanate ions, and the complex formed is extracted with monooctyl α-anilinobenzylphosphonate (MOABP) in chloroform. The molar absorptivity of the method is 5858 l mole^-1 cm^-1 at 470 nm. Beer's law is obeyed in the range 0.7–28 μg Mo ml^-1. Few metals interfere; the separation of the interfering elements is discussed. The composition of the extracted complex is Mo(SCN)₅·3 MOABP.     

Spectrophotometric determination of molybdenum in the presence of tungsten using gallein and benzyldodecyldimethylammonium bromide

The chemical similarity between molybdenum and tungsten makes the direct spectrophotometric determination of these metals impossible. Usually the determination is preceded by a separation step. In order to find out a selective and quantitative isolation method, coprecipitation with thioacetamide and Cu(II) as a carrier; MnO₂; cupferron, tannin and crystal violet; quinolin-8-ol, tannin and thioacetamide, were examined. Molybdenum(VI) could be determined in the presence of 100-fold mass excess of tungsten after precipitation with thioacetamide and Cu(II). The remaining methods could only be applied if mass excess of W is equal to or lower with respect to Mo. For the resolution of this problem, the derivative spectrophotometry was used. The studies of different order spectra of gallein complexes of molybdenum, tungsten and their mixtures have shown that the fifth-derivative spectra allows one to eliminate the interfering effects of W on the determination of Mo. At 650 nm the spectral features of tungsten is zeroing while the value of the fifth-derivative spectrum of mixture of Mo and W corresponds only to the concentration of molybdenum in the examined solution. Beer’s law is obeyed in the range 0.32–0.80 μg/mL of Mo. The developed derivative spectrophotometric method and the most selective pre-separation method, based on the precipitation of molybdenum(VI) sulphide, were applied to the determination of Mo in Armco iron and steel. The accuracy of the elaborated methods was confirmed by comparison of the determined content of Mo with certified values as well as with the result obtained by the reference ICP-OES technique.     

Direct determination of molybdenum in seawater by adsorption cathodic stripping square-wave voltammetry

A reliable and very sensitive procedure for the determination of trace levels of molybdenum in seawater is proposed. The complex of molybdenum with 8-hydroxyquinoline (Oxine) is analyzed by cathodic stripping square-wave voltammetry based on the adsorption collection onto a hanging mercury drop electrode (HMDE). This procedure of molybdenum determination was found to be more favorable than differential pulse cathodic stripping voltammetry because of inherently faster scan rate and much better linearity obtained through the one-peak (instead of one-of-two peaks) calibration. The variation of polarographic peak and peak current with a pH, adsorption time, adsorption potential, and some instrumental parameters such as scan rate and pulse height were optimized. The alteration of polarographic wave and its likely mechanism are also discussed. The relationship between peak current and molybdenum concentration is linear up to 150 mug l(-1). Under the optimal analytical conditions, the determination limit of 0.5 mug l(-1) Mo was reached after 60 s of the stirred collection. The estimated detection limit is better than 0.1 mug l(-1) of Mo. The applicability of this method to analysis of seawater was assessed by the determination of molybdenum in two certified reference seawater samples (CASS-2 and NASS-2) and the comparison of the analytical results for real seawater samples (study on a vertical distribution of Mo in the seawater column) with the results obtained by Zeeman-corrected electrothermal atomization atomic absorption spectrometry (Zeeman ETAAS). A good agreement between two used methods of molybdenum determination was obtained.     

General method for the liquid-liquid extraction of molybdenum and its application to neutron activation analysis

Summary The liquid-liquid extraction of Mo(VI) from different acid solutions by zinc diethyldithiocarbamate in chloroform is described. This extractant allows the separation of nanogram to milligram quantities of Mo from even gram quantities of many other elements. The separation of Mo can be made selective by appropriate choice of the composition of the aqueous phase, by back-extraction of Mo and/or the coextracted elements, and by masking Mo with hydrogen peroxide. These techniques were adapted for the determination of Mo in several reference materials by radiochemical neutron activation analysis via ⁹⁹Mo.     

用聚合表面活性剂作增敏试剂分光光度测定钼和钨

采用表面活性剂的分光光度分析法应用日趋广泛。这方面的研究工作虽极活跃,但较多工作限于已有经典表面活性剂的研究与应用,为分析化学的特定需要设计与合成新型表面活性剂的研究尚少。作者曾用环氧氯丙烷和长链烷基叔胺合成了以聚乙二醇为主链含有若干个带长链烷基的季氮支链的低聚合表面活性剂——聚(氧化丙烯)-α-十八烷基二甲基氯化铵(PPOSA)。实验表明,这类表面活性剂兼有阳离子和非离子表面活性剂的某些特性。本文     

RNAA for arsenic,cadmium, copper,and molybdenum in CNS tissues from subjects with age-related neurodegenerative diseases

Reactor thermal neutron irradiation of biological matrices induces high levels of intense gamma-ray or bremsstrahlung radiation from⁸²Br,⁴²K,²⁴Na, and³²P, that interfere with the determination of As, Cd, Cu, and Mo by INAA. Central nervous system (CNS) issue samples from subjects with Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and controls were analyzed using a simple RNAA procedure involving a rapid two-step solvent extraction procedure to determine these four elements. Significant increases (p0.05) in concentrations of Cd and Mo were observed for brain of AD subjects compared to controls, but significant imbalances were not observed for ALS subjects. Concentration data for these elements in selected international reference standards are also presented.