Determination Of Molybdenum In Sea Water Research Articles

α-ベンゾインオキシム溶媒抽出-ジメチルアミノフェニルフルオロン吸光光度法による海水中のモリブデンの定量

α-ベンゾインオキシム溶媒抽出-ジメチルアミノフェニルフルオロン吸光光度法による海水中のモリブデンの定量

Air-Segmented Continuous-Flow Analysis for Molybdenum in Various Geochemical Samples

An air-segmented continuous-flow method has been developed for the determination of molybdenum at ultra trace levels using the catalytic effect of molybdate during the oxidation of L-ascorbic acid by hydrogen peroxide. Incorporation of an on-line ion exchange column improved the tolerance limit for various ions. The detection limits with and without the column were 64 pmol L−1 and 17 pmol L−1, and the reproducibilities at 10 nmol L−1 were 2.1% and 0.2%, respectively. The proposed method was applied to the determination of molybdenum in seawater and lake water as well as in rock and sediment samples. This method has the highest sensitivity among the available literature to our knowledge, and is also convenient for routine analysis of molybdenum in various natural samples.

Application of Doehlert matrix and factorial designs in optimization of experimental variables associated with preconcentration and determination of molybdenum in sea-water by inductively coupled plasma optical emission spectrometry

A simple and efficient procedure for the preconcentration and determination of molybdenum in sea-water was developed using solid-phase extraction (SPE) of molybdenum(V) ion as the thiocyanate complex by polyurethane foam and inductively coupled plasma optical emission spectrometry (ICP-OES). The optimization process was carried out using two-level full factorial and Doehlert matrix designs. Four variables (solution volume, shaking time, thiocyanate concentration and hydrochloric acid concentration) were regarded as factors in the optimization. Results of the two-level full factorial design, 24 with 16 runs based on the variance analysis (ANOVA), demonstrated that all four factors, as well as the interactions between thiocyanate concentration and time and hydrochloric acid concentration and time, are statistically significant. Doehlert designs were applied in order to determine the optimum conditions for molybdenum preconcentration. The proposed procedure allowed molybdenum determination with a detection limit of 1.5 µg L−1 and a precision, calculated as relative standard deviation (RSD), of 1.8% for a set of 10 measurements for a molybdenum concentration of 10.0 µg L−1 in synthetic sea-water solution. The recovery of molybdenum in the presence of several cations achieved demonstrated that this procedure improved the required selectivity for sea-water analysis. The studied procedure was applied to molybdenum determination in surface sea-water samples collected in Salvador City, Brazil. Results showed good agreement with other reported data from the literature, including data obtained for samples from this same city by another procedure.

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 μg l −1. Under the optimal analytical conditions, the determination limit of 0.5 μg l −1 Mo was reached after 60 s of the stirred collection. The estimated detection limit is better than 0.1 μg 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.

Comparison of On-Column and Precolumn Derivatization for Liquid Chromatographic Determination of Molybdenum in Seawater and Bovine Liver

A rapid, accurate, and sensitive method was developed for the determination of molybdenum in seawater and bovine liver samples by reversed-phase liquid chromatography (LC) using a C18 column. The method was based on chelation of the metal with 8-hydroxyquinoline by on-column or precolumn derivatization followed by LC elution with acetonitrile-0.02M acetate buffer (3 + 2; pH 4.1) and 1 x 10(-3)M of the ligand as the mobile phase. The spectrophotometric detection was made at 390 nm. Data obtained from the 2 derivatizations (on- and precolumn chelation) were compared in terms of detection limit, precision, accuracy, and ease of LC determination of molybdenum. No significant difference exists in the detection limit and the sensitivity of the 2 methods. However, the on-column chelation method, that is, the direct injection of aqueous samples onto the column, showed relatively less interference from manganese and greater simplicity in operation compared with precolumn chelation; therefore, on-column chelation is preferable for routine analyses. The on-column method produced mean levels of 9.6 +/- 0.4 micrograms/L for the seawater sample and 3.6 +/- 0.2 microgram/g (certified value, 3.5 +/- 0.5 microgram/g) for bovine liver.

The voltammetric determination of Mo in seawater after adsorptive accumulation of the Eriochrome Blue Black R complex

A method for direct determination of molybdenum in seawater has been developed, and uses linear sweep voltammetry after adsorptive accumulation of the Erichrome Blue Black R (EBBR) complex on a static mercury drop electrode. To an acidified (pH 1.6) seawater (SW) sample, 6.0 × 10−6 M EBBR is added and preconcentration by adsorption is carried out for 30 s at a potential of −0.05 V vs. the Ag/AgCl/SW reference electrode. The potential is then scanned in the negative direction, giving a current peak for the reduction of the Mo—EBBR complex at −0.17 V. Under these conditions the limit of detection is 0.50 ng/mL. Experimental results for Mo in seawater using this technique agree well with certified values for two reference seawater samples (NASS-1, CASS-1).

Direct determination of molybdenum in seawater by adsorption voltammetry

Complex ions of molybdenum(VI) with 8-hydroxyquinoline (oxine) are shown to adsorb onto the hanging mercury drop electrode. This property forms the basis of a sensitive electrochemical technique by which dissolved molybdenum in seawater can be determined directly. The reduction current of adsorbed complex ions is measured by differential pulse adsorption voltametry, preceded by a period of 1 or 2 min of unstirred collection at an adsorption potential of -0.2 V. In the presence of 2 x 10/sup -3/ M oxine and at pH 2.5 the potential of the main reduction peak is located at -0.59 V. The peak current-molybdenum concentration relationship is linear up to 3 x 10/sup -7/ M; the detection limit is 4 nM. Greater sensitivity is obtained after stirred collection at pH 3.0 and with 10/sup -4/ M oxine, but the calibration curve is nonlinear. In these conditions the limit of detection lies at 10/sup -10/ M after 10 min stirred collection. 19 references, 8 figures.

Application of anion-exchange techniques to the determination of traces of molybdenum in sea-water

A combined ion-exchange spectrophotometric method has been developed for the determination of molybdenum in sea-water. Molybdenum is sorbed strongly on Amberlite CG 400 (Cl −) at pH 3 from sea-water containing ascorbic acid and is easily eluted with 6 M nitric acid. Molybdenum in the effluent can be determined spectrophotometrically with potassium thiocyanate and stannous chloride. The combined method allows selective and sensitive determination of traces of molybdenum in sea-water. The precision of the method is 2% at a molybdenum level of ~ 10 μg l .

Preconcentration with dithiocarbamate extraction for determination of molybdenum in seawater by neutron activation analysis

Molybdenum in seawater can be quantitatively extracted with pyrrolidinedithiocarbamate and diethyldithiocarbamate at pH 1.4 into chloroform, for neutron activation analysis. Uranium in seawater cannot be extracted at this pH, and hence eliminates the interference from the /sup 235/U(n,f)/sup 99/Mo reaction. Interferences from matrix species in seawater, such as sodium and bromine, are also removed during the extraction. The proposed method, with good accuracy and sensitivity, is suitable for the determination of molybdenum in natural waters. 10 references, 2 figures.

Determination of molybdenum in seawater by electron paramagnetic resonance spectrometry

Determination of molybdenum in seawater by electron paramagnetic resonance spectrometry

Selektivitätssteigerung katalytischer bestimmungsverfahren—extraktionskataly-metrische molybdänbestimmung

To increase the selectivity of catalytic methods, a solvent extraction and catalytic determination have been combined. By means of the determination of molybdenum based on the catalytic oxidation of 1-naphthylamine by bromate, it is shown that by selection of a suitable extraction system the catalyst can be determined directly in the organic extract. The catalytic activity of different complexes of molybdenum was tested and for an analytical application the extraction of molybdenum as oxinate was chosen. The method enables molybdenum to be determined down to 2.7 × 10 −9 M. The relative error of the determinations is 10%. 10 −4 M V, 2 × 10 −4 M Cr, 5 × 10 −5 M W and 10 −2 M Mn, Ni, Cu, Co, Fe, Mg, Zn, Cd, Al and Pb cause no interference. The method has been used for the determination of molybdenum in sea-water.