Direct Determination Of Molybdenum Research Articles

Direct Determination of Molybdenum in Milk and Infant Food Samples Using Slurry Sampling and Graphite Furnace Atomic Absorption Spectrometry

A fast and efficient method to determine molybdenum, Mo, in milk and other infant food by atomic absorption spectrometry with electrothermal atomization employing slurry sampling was developed. Slurries were prepared in ultrapure water with 5 to 20 min of sonication in concentrations of 10% w/v. The injection of 5.0 µL of a 0.1% (v/v) cetyl trimethyl ammonium chloride solution before the temperature program reduced the effect of build-up of carbonaceous residues within the atomizer. Europium (chemical modifier) and niobium (permanent modifier) were chosen for use from several potential modifiers. The parameters of merit were obtained in the optimized conditions Ta = 2,700 oC, Tp = 2,000 oC, tp = 20 s, and Eu 5.0 μg + permanent Nb 500.0 μg. These parameters were linear working range up to 100.0 μg/L, limit of detection (1.1 ± 0.1) μg/L, aqueous calibration, and standard addition curves with r2 > 0.9900 and relative standard deviation of 0.6% to 8.7%. The accuracy was evaluated by recovery tests and by certified material analysis; the agreement among these numbers validated the method. The powdered sample concentrations were between 39 and 1,570 µg/kg.

A novel and selective assay for the quantitative analysis of molybdenum(VI) at nanogram level by resonance light scattering quenching technique

A novel method is designed for the direct determination of trace amounts of molybdenum(VI) in tap water, human hair, and Chinese herbal medicine by means of decreasing resonance light scattering (RLS) technique. The characteristics of RLS spectra, the effective factors, and optimum conditions of the reaction were studied. In the medium of hydrochloric acid (pH 2.38), Mo(VI), dibromohydroxyphenylfluorone (DBHPF), and Triton X-100 react to form a complex, resulting in significant decreasing RLS signals of DBHPF–Triton X-100. The decreasing RLS intensity at 583.0 nm is proportional to the concentration of Mo(VI) up to 8.0 ng mL −1. The detection limit is 0.013 ng mL −1. The method is simple, reproducible, with reaction rapidity and stability of complexes formed. Moreover, the high selectivity and sensitivity of this method permits its direct determination of molybdenum(VI) in tap water, human hair, and Chinese herbal medicine and the results are in agreement with those obtained by the inductively coupled plasma atomic emission spectrometry (ICP-AES) method.

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.

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

The electrochemical behavior of the molybdenum complex of α-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.

Direct determination of molybdenum, chromium and manganese in seawater by graphite furnace atomic absorption spectrometry

Trace metals (molybdenum, chromium and manganese) in seawater have been determined directly by graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction. These methods are sensitive enough to determine these trace metals in seawater from the open ocean. Molybdenum has been determined using a simple calibration curve based on deionized water, whereas manganese and chromium have been determined with the method of standard additions. To determine molybdenum and manganese in coastal seawater or other contaminated seawater, a simple calibration curve based on deionized water suffices. The accuracy of the method is confirmed by analysis of certified reference saline waters, the analyzed values agreeing well with the certified values.

Direct determination of molybdenum in mineral waters by atomic absorption spectrometry with electrothermal atomization

A new method for the direct determination of molybdenum by ETA-AAS in mineral waters without prior separation or concentration is proposed. With careful control of the graphite furnace conditions selective volatilization of the salt matrix is successfully attained. The possible spectroscopic interference due to common metals as well as the reproducibility, precision and repeatability of the method has been studied and the molybdenum content of 21 mineral waters measured.

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.