Simultaneous polarographic determination of micro amounts of vanadium(V) and molybdenum(VI)

A simple and sensitive polarographic method has been developed for the determination of micro quantities of vanadium(V) and molybdenum(VI), based on the reduction of bromate, which is catalysed by these metal ions in the presence of 2,4-dihydroxyacetophenone oxime. Interference by various cations and anions has been investigated.     

Inorganic polarography in organic solvents-II: polarographic examination of the molybdenum(V) thiocyanate complex in diethyl ether

A procedure involving the solvent extraction of molybdenum(V) thiocyanate into diethyl ether followed by a direct polarographic examination of the organic phase offers a selective method for the determination of molybdenum down to 0.5 ppm. Only molybdenum, amongst 21 elements examined, is observed to give a reduction wave under the recommended conditions. The method is evaluated with respect to various experimental factors and is applied to the determination of molybdenum in mild and alloy steels.     

The polarography of molybdenum,titanium and niobium in solutions of organic acids

Further work on the polarographic reduction of molybdenum(VI), niobium(V) and titanium(IV) in base electrolytes containing organic acids is reported. A base electrolyte of 0.5 M citric acid-0.025 M sulphuric acid-0.05 M thorium nitrate proved suitable for the determination of molybdenum and titanium in the presence of niobium, tantalum, tungsten and zirconium. A direct polarographic method using this base electrolyte is described for the determination of molybdenum in a niobium base alloy.     

Enhanced sensitivity for the differential pulse polarographic determination of Mo(VI) based on adsorption catalytic current

A differential pulse polarographic (DPP) method based on the adsorption catalytic current in a medium containing chlorate and 8-hydroxyquinoline (oxine) is suggested for the determination of molybdenum(VI). Experimental conditions such as pH and the composition of supporting electrolyte have been optimized to get a linear calibration graph at trace levels of Mo(VI). The sensitivity for molybdenum can be considerably enhanced by this method. The influence of possible interferences on the catalytic current has been investigated. The sensitivity of the method is compared with those obtained for other DPP methods for molybdenum. A detection limit of 1.0 × 10^–8 mol/L has been found.     

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.     

Polarographic Determination of Thorium at Trace Level

Abstract

An indirect method has been developed For the determination of thorium(IV) at trace level, by means of the Formation of 11-molybdothorophosphoric acid, its isolation with an organic solvent, stripping with alkali and measurement of the molybdenum(VI) by its catalytic effect on the polarographic reduction of hydrogen peroxide. A detection limit of 0.067 mg/l can be achieved.     

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.     

Use of less polar organic solvents for the polarographic determination of metals after extraction of their diethyldithiocarbamates

Summary Physico-chemical parameters of various organic solvents, such as conductivity, viscosity, available potential range and phase-separation characteristics, have been evaluated for the use of direct polarographic analysis after liquid-liquid extracxtion. Due to its higher conductivity of 1.16 mS cm^–1 and a wide available potential range of 0.81 –1.72 V vs. Ag/AgCl, a dichloromethane solution containing 0.1 mol/l tetrabutylammonium perchlorate is chosen as the best organic solvent solution for the purpose of this study. Bismuth(III) is extracted into the organic phase and gives well-defined anodic and cathodic waves at –0.12 V and –0.51 V, respectively. A selective polarographic determination of the metal after the dichloromethane extraction has been developed.     

痕量苯酚的单扫描极谱法测定

研究了碱性介质中苯酚与对氨基苯磺酸重氮盐所形成偶氮化合物的极谱行为，并建立了痕量苯酚的极谱测定方法。方法用于污水中微量苯酚的测定，结果令人满意。     

Differential pulse polarographic determination of orthophosphate in aqueous media

The determination of orthophosphate in aqueous media by differential pulse polarography is described. It is based on determination of the molybdenum in 12-phosphomolybdic acid. High sensitivity is achieved by measuring the polarographic wave due to the catalytic reduction of perchlorate or nitrate in the presence of molybdenum(VI). The method is suitable for samples as small as 3.5 ml which contain as little as 9 ng of phosphorus per ml. The average relative deviation is 3.0% at the 0.045 mg/l. phosphorus level and 1.6% at the 1.2 mg/l. level. Results for the analysis of EPA quality-control water and real surface-water samples are reported.     

Differential pulse polarographic determination of trace amounts of vanadium and molybdenum in various standard alloys and environmental samples after preconcentration of their morpholine-4-carbodithioates on microcrystalline naphthalene or morpholine-4-dithiocarbamate cetyltrimethyl-ammonium bromide-naphthalene adsorbent

A highly selective, sensitive, and fairly rapid and economical differential pulse polarographic (DPP) method has been reported for the determination of trace amounts of vanadium and molybdenum in standard alloys and various environmental samples. The morpholine-4-carbodithioates of these metals were retained (>99% recovery) quantitatively on microcrystalline naphthalene in the pH range 4.5-6.9 for vanadium and 1.5-4.5 for molybdenum. These metals were determined by DPP after desorption with 10 ml of 1 M HCl. Vanadium and molybdenum may also be preconcentrated by passing their aqueous solutions under similar conditions on morpholine-4-dithiocarbamate CTMAB-naphthalene adsorbent packed in a column at a flow rate of 1-5 ml min(-1) and determined similarly. The detection limits are 0.20 ppm for vanadium and 0.04 ppm for molybdenum at minimum instrumental settings (signal to noise ratio=2). The linearity is maintained in the following concentration ranges, vanadium 0.50-10.0 and molybdenum 0.10-9.0 ppm, with a correlation factor of 0.9996 (confidence interval of 95%, slopes 0.0196 and 0.01497 muA mug(-1), intercepts 3.65x10(-3) and -1.92x10(-3) respectively) and relative standard deviation of 1.1% in the microcrystalline method, while in the column method, the linearity is maintained in the concentration ranges, 0.50-6.5 for vanadium and 0.10-5.5 ppm for molybdenum with correlation factor of 0.9994 (with confidence interval of 95%, slopes 0.0194, 0.015 muA mug(-1), intercepts 3.60x10(-3) and -1.90x10(-3) respectively) and relative standard deviation of 1.4%. Various parameters such as the effect of pH, reagent, naphthalene and CTMAB concentrations, volume of aqueous phase and interference of a large number of metal ions on the estimation of vanadium and molybdenum have been studied in detail to optimize the conditions for their voltammetric determination at trace level in various standard alloys and environmental samples.     

Pulse Polarographic: Determination of Nanogram Amounts of Ortho-Phosphate

Abstract

A procedure has been developed for the pulse polarographic determination of nanogram amounts of ortho-phosphate based on the reduction of molybdenum blue formed from 12-molydophosphate. The molybdenum blue is extracted into iso-amyl alcohol from acid solution, and the extract is then washed free of excess molybdate with dilute sulphuric acid. Finally, the molybdenum blue is back-extracted into a tartrate buffer and is pulse polarographed. Precise determinations can be made on 10 ng of PO₄ ³ ml^?11 in the polarographed solution. Determinations have been made on standard and sample ortho-phosphate solutions at the 2 ng of PO₄ ³ ml^?11 level by effecting a five-fold concentration at the extraction step.     

极谱法测定化探样品中钨钼的技术改进

针对传统极谱法测定化探样品中钨钼时操作手段繁琐问题加以改进。试样以硫酸-二苯乙醇酸-二苯胍-氯酸钠体系为混合底液,将经过碱熔融后的样品以甲基橙为指示剂,用硫酸(1+1)调酸度后,加入固定比例的混合底液,摇匀,无需定容,放置25~30min后直接测定。采用二次倒数波测定,钨峰电位在-660mV左右,钼峰电位在-30mV左右,钨钼的质量浓度在0.02~1.0μg/mL内呈线性关系,钨检出限为0.5μg/g,钼检出限为0.3μg/g。方法灵敏度高,快捷、简单,适用于大批量化探样品的测定。     

Determination of aluminium in plutonium metal by differential linear sweep oscillographic polarography

A procedure has been developed for the polarographic determination of aluminium in plutonium. The plutonium is separated by anion-exchange in a nitrate medium, and the aluminium is determined in the eluate by use of Superchrome Garnet Y. The aluminium concentration range in the polarographed solutions is 0.020–0.800 μg/ml. The average recovery of aluminium was 99.3 %, relative standard deviation 7.2%. Of 20 common impurities found in plutonium métal, only molybdenum and titanium cause significant interference; both can be removed by ion-exchange.     

A microcomputer-based data acquisition and processing system for electrochemical analysis

The system described for electrochemical analysis includes ensemble averaging, boxcar integration and background subtraction. A digital storage oscilloscope interfaced to a microcomputer provides these data-processing techniques for the differential pulse polarographic determination of molybdenum. The system is easily interfaced to the polarograph. An approximately four-fold improvement in the detection limit for molybdenum — to 2.7 × 10^-4 ppm — was achieved by using a combination of ensemble averaging and background subtraction.     

Simultaneous determination of tungsten and molybdenum in sea water by catalytic current polarography after preconcentration on a resin column

The simultaneous determination of tungsten and molybdenum in sea water is based on preconcentration by column extraction with 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (Kelex- 100) resin, and measurement of the polarographic catalytic currents obtained in a solution of chlorate, benzilic acid and 2-methyl-8-quinolinol. When the concentration factor is 50, the detection limits are 2.4 pM for tungsten and 17 pM for molybdenum (for a signal-to-noise ratio of 3). The precision of the determination is ca. 10% for 67 pM tungsten and ca. 5% for 106 nM molybdenum in sea water (n=4). Results for sea water and other natural waters are presented.     

Polarography of metal-gallic complexes

The polarographic behavior of metal ions in perchlorate media containing gallic acid is described. Tungsten(VI) forms a complex with gallic acid which yields a single wave in these media, useful in the polarographic determination of tungsten. Evidence for complexation of chromium(III), copper(II), iron(III), molybdenum(VI), uranium(VI), vanadium(V), tungsten(VI), praseodymium(III), samarium(III), neodymium(III) and gadolinium(III) is obtained and the behavior of these metal ions is summarized.     

Application of differential pulse polarography for trace determination of polycytidylic acid in absence and presence of some metal ions

Summary A differential pulse polarographic method has been applied to the determination of trace concentrations of polycytidylic acid (Poly-C) in absence and presence of metal ions. The applicability of differential pulse polarography for the trace determination of the investigated biological compound was examined with regard to the dependence of differential pulse current on various parameters such as pH, pulse amplitude, scan rate and drop time. The selectivity of this technique for the determination of binary and a ternary mixtures of poly-C and some metal ions has been also reported. Limits of detection and quantitation have been calculated for the differential pulse polarographic determination of the poly-C and various metal ions. The validity of this method is supported by the constancy of the i_p/C values and a statistical analysis is included on calibration curve parameters and observed concentration.     

Indirect determination of thallium by differential-pulse polarography

The method is based on the separation of Tl(I) as Tl(2)HPMo(12)O(40), stripping of the molybdate, and measurement of the peak current in differential-pulse polarography of the molybdenum. The calibration graph is linear over the range 2-12 ppm of thallium. The relative standard deviation is 1.2% (7 replicates each containing 500 microg of thallium). The current due to reduction of the molybdenum is three times that for reduction of the equivalent amount of Tl(I) in the thallous phosphomolybdate precipitate, making the indirect approach more sensitive than direct polarographic determination of the Tl(I).     

Indirect polarographic microdetermination of chlorine or bromine in organic compounds

A polarographic method for the microdetermination of chlorine or bromine in organic compounds is based on oxygen-flask combustion followed by an exchange reaction of chloride or bromide with excess of solid silver chromate, and polarographic determination of the chromate liberated. The method has been applied satisfactorily to a wide range of chlorine or bromine organic compounds with a coefficient of variation not exceeding 1%.