Spectrophotometric determination of molybdenum using surfactant-mediated liquid--liquid extraction

A new spectrophotometric method has been developed for determination of molybdenum using surfactant-mediated liquid--liquid extraction. Molybdenum(V) obtained by ascorbic acid reduction in 2.5 M H2SO4 reacted spontaneously with thiocyanate and cetyl trimethyl ammonium bromide (CTAB), forming an intense orange yellow complex that was extracted quantitatively into 1,2-dichloroethane and absorbed at 460 nm. The absorbance of the extract was found to be stable for more than 24 h. Beer's law was obeyed over the concentration range 0.1--4.2 m g Mo mL-1 of the extract. The linear range for an accurate determination was found to be 1.2--2.6 m g Mo mL-1. The molar absorptivity and LOD of the procedure were 4.01 \times 104 L mol-1 cm-1 and 0.00239 m g Mo mL-1, respectively. The stoichiometry of the orange yellow complex (Mo:SCN:CTAB) was found to be 1:3:2. The effect of a large number of cations, anions, and complexing agents was studied. For 10 replicate determinations of 1 m g Mo mL-1, the standard deviation was 0.014 concentration units with a relative mean error of \pm 0.38%. The method developed was applied for determination of molybdenum in various alloy steels and a wide variety of biological and environmental samples, including different types of water samples.