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.     

Catalytic spectrophotometric determination of molybdenum (VI) with the hydrazine-metanil yellow system

A new catalytic Spectrophotometric method for the determination of trace amounts of molybdenum (VI) has been proposed. The method is based on the catalytic effect of Mo(VI) on the reduction of metanil yellow by hydrazine dihydrochloride. Under experiment condition, the linear range of determination is 20–160 ng/mL for molybdenum and the detection limit is 11.2ng/mL. The method has been used to determine trace molybdenum in bean samples with the recovery of 96.0–99.0%, with relative standard deviations of 1.50–2.53%.     

A rapid spectrophotometric method for the determination of molybdenum in industrial, environmental, biological and soil samples using 5,7-dibromo-8-hydroxyquinoline.

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amount of molybdenum(VI) using 5,7-dibromo-8-hydroxyquinoline (DBHQ) has been developed. 5,7-Dibromo-8-hydroxyquinoline reacts in a slightly acidic solution (0.05 - 1.0 M H2SO4) with molybdenum(VI) to give a deep greenish-yellow chelate which has an absorption maximum at 401 nm. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell's sensitivity were found to be 4.13 x 10(3) L mol(-1) cm(-1) and 7 ng cm(-2) of molybdenum(VI), respectively. Linear calibration graphs were obtained for 0.1 - 50 microg mL(-1) of molybdenum(VI). The stoichiometric composition of the chelate is 1:3 (Mo:DBHQ). A large excess of over 50 cations, anions and some common complexing agents (e.g. EDTA, oxalate, citrate, phosphate, thiourea, SCN-) do not interfere with the determination. The method was successfully used in the determination of molybdenum in several Standard Reference Materials (alloys, steels and waters) as well as in some environmental waters (inland and surface), biological samples (human blood and urine), soil samples, solution containing both molybdenum(V) and molybdenum(VI) and complex synthetic mixtures. The method has high precision and accuracy (S = +/-0.01 for 0.5 microg mL(-1)).     

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.     

Letter to the Editor

Abstract

The experiments show that Mo(VI) has very strong catalytic effect on the slow redox reaction between methyl orange and hydrazine sulfate in sulphuric acid medium at 100°C. And methyl orange exhibits a sensitive second derivative wave at ?0.72 V vs. SCE in the supporting electrolyte of NaOH. This provides a novel catalytic method for the determination of trace amounts of molybdenum using linear scan voltammetry as detection technique. A Calibration graph from 1 to 80 ng/ml and detection limit of 0.3 ng/ml Mo were obtained by the fixed-reaction time procedure. This new catalytic method has been applied to determining molybdenum in ore and standard steel samples, with excellent results.     

Spectrophotometric determination of trace molybdenum in plants and seeds with 3,5-dibromo-4-hydroxyphenylflurone

A novel spectrophotometric method based on a new reagent, 3,5-dibromo-4-hydroxyphenylflurone, was developed for the determination of molybdenum in plants and seeds. 3,5-Dibromo-4-hydroxyphenylflurone showed outstanding analytical characteristics for spectrophotometric determination of molybdenum. The reaction conditions are simple and stable. In 0.2 mol l(-1) phosphoric acid medium (which can combine with iron and other metal ions and greatly improves the selectivity of the color system), molybdenum(VI) reacts with 3,5-dibromo-4-hydroxyphenylflurone to form a 1:2 red complex with an absorption maximum at 530 nm, the color reaction can completed in 2 min and the absorbance of the molybdenum complex remains stable for at least 72 h at room temperature. Its stability constant is 1.21 x 10(28) at 25 degrees C. Beer's law is obeyed over the range 0-0.6 microg ml(-1) Mo(VI). The reagent has very high sensitivity and selectivity; the molar absorptivity of the complex is 1.35 x 10(5) 1 mol(-1) cm(-1) and the limit of quantification, the limit of detection and relative standard deviation (n = 10) were found to be 6.7 ng ml(-1), 2.2 ng ml(-1) and 1.01%, respectively. Cu (50000-fold), Fe (20000-fold), K (20000-fold), NH4+ (20000-fold), Mg (15000-fold), Zn (10000-fold), Na (10000-fold), Al (4000-fold), Ca (25000-fold), Mn (2000-fold), Ce (500-fold), Cr (400-fold) and Bi (200-fold) do not interfere with the determination of trace levels of molybdenum up to the excesses indicated. The selectivity is much superior to that of other published methods. The proposed method was applied to the direct determination of molybdenum in plants and seeds with satisfactory results. The synthesis of the reagent and conditions of color reaction were studied in detail.     

Simultaneous voltammetric determination of molybdenum and copper by adsorption cathodic differential pulse stripping method using a principal component artificial neural network

An adsorption differential pulse stripping method for the simultaneous determination of molybdenum and copper based on the formation of their complexes with cupferron (benzene, N-hydroxy-N-nitroso) is proposed. The optimum experimental conditions were obtained 0.010 mM cupferron, pH 3.0, accumulation potential of -0.15 V versus Ag/AgCl, accumulation time of 60 s, scan rate of 10 mV s(-1) and pulse height of 50 mV. Molybdenum and copper peak currents were observed at -0.16 and +0.02 V, respectively. A principal component artificial neural network (PC-ANN) was utilized for the analysis of the voltammogram data. A three layer back-propagation network was used with sigmoidal transfer function for the hidden and the output layers. The linear dynamic ranges were 5.0-60.0 and 0.1-20.0 ng ml(-1) for Cu(II) and Mo(VI), respectively. The detection limit was 0.06 ng ml(-1) for Mo(VI) and 0.20 ng ml(-1) for Cu(II). The capability of the method for the analysis of real samples was evaluated by the determination of molybdenum and copper in river water, tap water, and alloy.     

Adsorbing colloid flotation separation and polarographic determination of Mo(VI) in water

A method is described for the flotation and determination of Mo(VI) in water at ng/ml levels. Mo(VI) is preconcentrated and separated by adsorbing colloid flotation employing aluminium(III) hydroxide as collector and sodium lauryl sulphate as surfactant at pH 5.3 ± 0.1. The molybdenum content in the froth is estimated by using the catalytic wave of Mo(VI) in the presence of nitrate by charging current compensated d.c. polarography (CCCDCP) or differential pulse polarography (DPP). The effect of variables such as pH, ionic strength, concentration of collector and surfactant, time of stirring and gas flow-rate on the recovery of Mo by flotation is reported. The effects of various cations and anions on the flotation and determination of Mo are studied. This method is employed for the determination of molybdenum in natural fresh water samples.     

Spectrophotometric determination of trace amounts of molybdenum (VI) based on catalytic reduction of safranine by hydrazine dihydrochloride

Summary A simple and rapid kinetic method for the determination of traces of molybdenum (0.1–4.0 g/ml) based on its catalytic effect on the reduction of safranine by hydrazine dihydrochloride is reported. The reaction is monitored spectrophotometrically by measuring the decreasing absorbance of safranine at 520 nm by the fixed time method. The method is sensitive, precise and free from interferences from many anions and cations. The experimental limit of detection is 100 ng/ml and the relative standard deviation for 1.0 g/ml Mo(VI) is 1.56%. The procedure was successfully applied to the determination of molybdenum in a steel alloy.     

A highly sensitive assay for protein using resonance light-scattering technique with dibromohydroxyphenylfluorone-molybdenum(VI) complex

At pH 2.8 and in the presence of 0.090% p-octylpolyethyleneglycol phenylether, the resonance light-scattering (RLS) spectrum of molybdenum(VI) complex with dibromohydroxyphenylfluorone (DBHPF) has a sharp peak at 586 nm. If the micro protein coexists with Mo(VI) and DBHPF, the RLS intensity of the complex at 586 nm is significantly enhanced by protein due to the binding interaction between protein and DBHPF-Mo(VI) complex. Based on this a new assay for protein is described. The dynamic ranges for bovine and human serum albumins are both 0.05-0.75 mg l-1 with detection limits of 13 and 15 ng ml-1, respectively. Besides high sensitivity, the method is characterized by good reproducibility, rapidity of reaction, good stability of chemical system, commonality of spectrofluorometer, few coexisting substances, especially detergents. The determinations of diluted human serum and urine by this method give the results very close to these by the Coomassie brilliant blue G-250 colorimetry, with relative standard deviations of five duplicates of 1.8-2.5%.     

Simultaneous voltammetric determination of Mo(VI) and W(VI) by adsorptive differential pulse stripping method using adaptive neuro-fuzzy inference system

An adsorptive differential pulse stripping method is proposed for the simultaneous determination of molybdenum and tungsten based on the formation of their complexes with a novel proton transfer compound, [phenH]⁺[pyzdc]^?, containing both pyrazine-2,3-dicarboxylic acid and 1,10-phenanthroline. The optimum experimental conditions were obtained using 0.052 mM [phenH]⁺[pyzdc]^? ligand, pH 3.3, accumulation potential of ?0.1 V versus Ag/AgCl, accumulation time of 60 s and scan rate of 33.3 mV/s. An adaptive neuro-fuzzy inference system (ANFIS) was utilized for the analysis of the voltammogram data. The detection limits were 4.0 ng/mL for Mo(VI) and 3.0 ng/mL for W(VI). The influence of potential interfering ions on the determination of molybdenum and tungsten was studied. The procedure was applied to the simultaneous determination of molybdenum and tungsten in some water samples.     

Determination of trace molybdenum in vegetable and food samples by spectrophotometry with p-carboxyphenylfluorone

A new highly sensitive and selective chromogenic reagent, p-carboxyphenylfluorone (p-CPF), was studied for spectrophotometric determination of trace molybdenum. In 0.36 mol L(-1)phosphoric acid medium, p-CPF reacts with molybdenum(VI) to form a 1:3 red complex, which has a sensitive absorption peak at 531 nm. Under optimal conditions, the reaction of molybdenum(VI) with p-CPF completed rapidly and absorbance remains almost constant for at least 24 h. Molybdenum(VI) obeyed Beer's law in the range 0-2.0 microg mL(-1); the apparent molar absorption coefficient, Sandell's sensitivity and the limit of detection were found to be 1.03 x 10(5) L mol(-1) cm(-1), 1.028 ng cm(-2)and 0.73 ng mL(-1) respectively; the effect of various foreign ions were examined in detail. It was found that most coexisting ions can be tolerated in considerable amounts, especially 800 mg of Mn(II), 200 mg of Mg(II), Fe(II), Co(III), Ni(II) and Cd(II), 50 mg of Ca(II) and Al(III), 25 mg of Cu(II) and Fe(III), 10 mg of Hg (II), La(III), Bi(III), Pb(II) and Zn(II) don't interfere with the determination of molybdenum(VI). The proposed method is very simple, sensitive and selective, it has been applied to determine molybdenum in vegetable and food samples with a very high precision and accuracy. Moreover, the synthesis of the reagent and the conditions of the colour reaction were also studied in detail.     

Application of adsorptive cathodic differential pulse stripping method for simultaneous determination of copper and molybdenum using pyrogallol red

A reliable and sensitive procedure for the simultaneous determination of trace levels of copper and molybdenum is proposed. The complexing of copper(II) and molybdenum(VI) with pyrogallol red (PGR) is analyzed by cathodic stripping differential pulse voltammetry based on the adsorption collection of the complexes onto a hanging mercury drop electrode (HMDE). The effect of chemical and instrumental parameters on the sensitivity and selectivity were studied. Copper and molybdenum peaks potential were observed at about +0.13 and −0.22 V versus Ag/AgCl electrode, respectively. A standard addition method was utilized for the analysis of voltammogram data, under the optimum conditions and with accumulation time of 90 s. The measured peak current at about +0.14 and −0.22 V is proportional to the concentration of Cu(II) and Mo(VI) over the range of 2-70 and 0.8-80 ng ml⁻¹, respectively. The limit of detection are 0.3 and 0.1 ng ml⁻¹ for Cu(II) and Mo(VI), respectively. The capability of the method for the analysis of real samples was evaluated by determination of copper and molybdenum in river water, tap water and alloy. Atomic absorption spectrometry was applied as a reference method for determination of copper and molybdenum in water samples.     

Ultra trace analysis of molybdenum by differential pulse polarography and adsorptive stripping voltammetry in the presence of 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone

Summary Different polarographic and voltammetric techniques for the determination of molybdenum at the trace level have been investigated. As a result, a new high-sensitivity procedure for the determination of molybdenum by adsorptive stripping voltammetry was developed. The method is based on the reaction of molybdenum(VI) with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) to produce a complex which is absorbed onto mercury at –0.20 V (vs. Ag/AgCl, 3 mol/l KCl) from pH 2.7 solution. The cathodic stripping peak at –0.62 V can be used to determine molybdenum with a detection limit of 0.02 ng/ml after 5 min deposition time. The relative standard deviation for the determination of 0.1 ng/ml Mo after 5 min stirred collection was 6.6%. Interference from various inorganic ions and organic substances are reported. The method was applied to the determination of molybdenum traces in waters; interfering organic substances in polluted waters were destroyed by oxidative digestion in a microwave oven.     

A resonance light scattering method for the determination of uranium based on a water-soluble salophen and oxalate

A resonance light scattering (RLS) method for the direct detection of uranium (VI) or uranyl in aqueous solution without separation procedure has been reported in this paper. Sulfo-salophen, a water-soluble tetradentate Schiff base ligand of uranyl, reacted with uranyl to form a complex. The complex reacted further with oxalate to form supramolecular dimer with large molecular volume, resulting in a production of strong RLS signal. The amount of uranium (VI) was detected through measuring the RLS intensity. A linear range was found to be 0.2–30.0 ng/mL under optimal conditions with a detection limit of 0.15 ng/mL. The method has been applied to determine uranium (VI) in environmental water samples with the relative standard deviations of less than 5 % and the recoveries of 98.8–105.8 %. The present technique is suitable for the assay of uranium (VI) in environmental water samples collected from different sources.     

Adsorptive stripping voltammetric determination of traces of molybdenum in natural water in the presence ofα-benzoinoxime

The electrochemical behavior of the molybdenum complex of -benzoinoxime was investigated using cyclic voltammetry and linear scan voltammetry, after adsorptive accumulation of the complex onto a hanging mercury drop electrode (HMDE). The signal corresponds to the reduction of molybdenum in the complex adsorbed at the HMDE surface. Under optimal conditions, the adsorptive stripping voltammetric procedure gave an extremely low detection limit of 0.1 nM (9.6ng/l) Mo(VI) following stirred accumulation for 5 min at 0.0 V (vs. Ag/AgCl). The reduction cur rent-[Mo(VI)] relationships were linear up to 25 and 100 nM. Repetitive determinations of 10 nM solutions gave relative standard deviations of 2.2 and 3.5%, for 1 and 5-min accumulation periods, respectively. Most of the ions investigated did not interfere with the determination of molybdenum, except for tungsten. Excellent selectivity against copper was observed. The proposed procedure was applied to the direct determination of molybdenum in natural water.     

Flow-injection catalytic determination of molybdenum with blamperometric detection in a microprocessor-controlled system

The flow-injection determination of molybdenum(VI) is based on its catalytic effect on the oxidation of iodide by hydrogen peroxide. The triiodide ion formed in this reaction is detected amperometrically in a flow-through cell containing two platinum wire electrodes polarized at 100 mV. After optimization of the measuring conditions, the detection limit is 1.2 μg l^?1 Mo(VI) and the linear range extends to 1 mg l^?1. Interference of various metal ions and their removal is described. The procedure was tested on the determination of molybdenum(VI) in soil extracts.     

QuEChERS与液相色谱-串联质谱联用检测中药、调味品及外敷药物中去甲乌药碱的含量

针对中药材、调味品及外敷药物中的去甲乌药碱,建立了一种基于QuEChERS前处理与液相色谱-串联质谱（LC-MS/MS）联用的检测新方法。样品经甲酸-乙醇提取、QuEChERS吸附剂净化后,样品溶液引入LC-MS/MS进行分析,在多反应监测模式下检测。该方法的检出限为0.03 ng/g,线性范围为0.10~100 ng/g,精密度为4.33%（0.50 ng/g,n=7）。采用所建立的方法对市售的13种中药、4种调味料及1种藏药贴膏中的去甲乌药碱含量进行了检测,在干荷叶、干莲子、山药、玉竹、淮山、花椒、桂皮及骨痛贴膏中检出去甲乌药碱,其含量分别为9667.6、1183.8、21.5、8.2、8.5、148.6、21.3、173.3 μg/kg。对花椒和桂皮进行加标回收试验,回收率在92.6%~109.8%之间,表明所建立的方法具有良好的准确性。综上,该方法具有快速、简便、可靠、可批处理的优点。     

Kinetic-Spectrophotometric Determination of Molybdenum(VI) Based on Its Catalytic Effect on the Thionine-Hydrazine Reaction

Abstract

A kinetic method for the determination of trace amounts of Mo(VI) (0.05-4 μg ml^?1) based on its catalytic effect on the reduction of thionine by hydrazine monochloride in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 605 nm after a fixed time (5 min.). The detection limit of the method is 23 ng ml^?1 and the relative standard deviation (RSD) for 0.05 μg ml^?1 of Mo(VI) is 1.2% (n=7). The method is almost free from interferences, especially from large amounts of tungsten. The procedure was successfully applied to the determination of trace amounts of molybdenum in steel.     

Determination of proteins with tetracarboxy manganese(II) phthalocyanine by resonance light scattering technique

A novel method for the determination of proteins by using tetracarboxy manganese(II) phthalocyanine (MnC4Pc) as a resonance light scattering (RLS) probe has been developed. At pH 3.0 Britton-Robinson (B-R) buffer solution, the RLS intensity of MnC4Pc at 385 nm is greatly enhanced in the presence of proteins. The effects of pH, reaction time, concentration of MnC4Pc and interfering substances on the enhanced RLS intensity are investigated, respectively. Under optimal conditions, the linear ranges of the calibration curves are 0-2.00 microg mL(-1) for bovine serum albumin (BSA) and human serum albumin (HSA), 0.0-1.75 microg mL(-1) for human-IgG and ovalbumin, with a detection limit of 16.37 ng mL(-1) BSA, 17.62 ng mL(-1) HSA, 19.41 ng mL(-1) human-IgG and 20.72 ng mL(-1) ovalbumin. The method has been applied to the determination of total proteins in human serum samples collected from a hospital and the results are in good agreement with those reported by the hospital.