Molybdenum (Mo) is a biologically important trace element which occurs in various oxidation states. However, as with other trace metals, what is essential in tiny amounts can be highly toxic at larger doses [1]. Prolonged exposure to Mo in the environment can cause toxicity to humans, animals, and plants [2]. Therefore, it is important to monitor Mo in a wide range of natural samples. Owing to the low concentration of molybdenum in natural samples, a preconcentration step is required prior to its determination [3]. Herein, a novel method based on coacervative liquid-phase microextraction prior to UV-Vis spectrophotometry for determination of molybdenum at trace levels in environmental samples is proposed. The method is based on the reaction of Mo with thiocyanate (SCN-) as a chelating agent in acidic medium. The colored complex of molybdenum is then extracted with decanoic acid which has been dissolved in THF. The coacervates form instantaneously, and two phases are separated by centrifugation. The upper phase is transferred into a micro-cuvette to be determined by UV-Vis spectrophotometry. Absorbance of the complex was measured at 470 nm. Several important relevant parameters such as the amount of decanoic acid and THF, concentration of sulfuric acid and extraction time have been investigated. Under optimum operating conditions, the calibration curve was plotted which was linear in the concnetration range of 5 to 50 ng mL-1 of Mo. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were obtained to be 1.3 ng mL-1 and 4.3 ng mL-1, based on 3sb/m and 10sb/m criteria, respectively. The relative standard deviation (RSD%) of the method was found to be 3% for ten replicate measurement. The potential chemical interferences were studied and discussed. The accuracy of the proposed method was validated through the analysis of CRM‐ TMDW‐ 500 (Certified Reference Material Trace Metals in Drinking Water) and the results obtained were in good agreement with the certified values. The proposed method has been successfully applied for the determination of the Molybdenum in raw and spiked river and well water samples with recoveries in the range of 97-98 %.

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