Background Chemistry of Molybdenum
Molybdenum analysis
Bead sorbent Perloza MT 50 was used for selective removal of metal W, Mo, V, Ge, and Sb oxoanions. All experiments were carried out by dynamic column sorption. Sorption of tungstate and molybdate anions was successful. The sorption capacity decreased with increasing concentration of accompanying anions (chlorides, sulphates) and with increasing pH (3.5-5.5). Sorption of vanadate anion was possible but the sorption capacity was very low. Sorption of Ge(IV) and Sb(III) oxoanion was negligible.
Mistova, E., Parschova, H., and Matejka, Z., Selective sorption of metal oxoanions from dilute solution by bead cellulose sorbent, Separation Science and Technology, 2007, 42, 1231-1243.
Molybdenum concentration is usually very low in environmental samples and the sample matrix may cause serious interferences during measurement. Preconcentration and separation methods are needed to solve these problems and render more sensitive, accurate and interference-free determination. Recent developments in sample treatment — solid phase and liquid-liquid extraction as well as coprecipitation — are presented, including flow-based methodology. In addition, important extension and improvements in analytical methods for determinations of molybdenum are updated. Some examples of speciation analysis are also presented.
Pyrzynska, K., Determination of molybdenum in environmental samples, Analytica Chimica Acta, 2007, 590, 40-48.
Water molybdenum analysis
A cloud-point extraction process using
micelle of the cationic surfactant CTAB to extract Mo(VI) from aqueous
solutions was investigated. The detection limit of the method was 0.1 ng mL-1.
The relative standard deviationand
relative error for five replicate measurements of 65.0 ng mL-1 Mo(VI) were 1.1% and 1.9%. The method was applied to the determination of
molybdenum(VI) in steels and tap water and well water samples.
Madrakian, T. and Ghazizadeh, F., Cloud-point preconcentration and spectrophotometric determination of trace amounts of molybdenum(VI) in steels and water samples, Journal of Hazardous Materials, 2008, 153, 695-700.
Trace molybdenum in water and biological samples
A new method has been developed for the determination of trace molybdenum based on separation and preconcentration with TiO2 nanoparticles immobilized on silica gel (immobilized TiO2 nanoparticles) prior to its determination by graphite furnace atomic absorption spectrometry (GFAAS). Molybdenum can be quantitatively retained by immobilized TiO2 nanoparticles at pH 1.0 and separated from the metal cations in the solution, then eluted completely with 0.5 mol L-1 NaOH. The detection limit of this method for Mo was 0.6 ng L-1 with an enrichment factor of 100, and the relative standard deviation (RSD) was 3.4% at the 10 ng mL-1 Mo level. The method has been applied to the determination of trace amounts of Mo in biological and water samples.
Liang, P., Li, Q., and Liu, R., Determination of trace molybdenum in biological and water samples by graphite furnace atomic absorption spectrometry after separation and preconcentration on immobilized titanium dioxide nanoparticles, Microchimica Acta, 2009, 164, 119-124.
Trace molybdenum in environmental and biological samples
A novel and sensitive spectrophotometric method for the determination of molybdenum at trace levels in environmental and biological samples is proposed. The method is based on the reaction of Mo(V) with thiocyanate (SCN-) and methyltrioctyl ammonium chloride (MTOAC) in acidic medium. The red colored complex of molybdenum is extracted with N-phenylbenzimidoyl thiourea (PBITU) in 1-pentanol for its determination by spectrophotometry. The sensitivity of the present method is higher than other conventional thiocyanate method, due to the use of MTOAC in liquid-liquid extraction. The value of molar absorptivity of the complex with respect to molybdenum is 7.6 x 104 Lmol-1 cm-1 at 470 nm. The limit of detection of the metal is 5 ng mL-1. The system obeys Beer's law between 20 and 1000 ng mL-1 with slope, intercept and correlation coefficient values of 0.81, 2.5 x 10-3 and +0.999, respectively. Most of the metal ions tested did nor interfere in the determination of molybdenum. The proposed method has been applied for the determination of the rnolybdenum in environmental and biological samples.
