Sensitive method for the determination of molybdenum in natural groundwater at sub-ppb levels using DLLME coupled with ETAAS

Abstract

Molybdenum is an essential trace element of biological and environmental relevance. Monitoring its content in water sources is very important from the standpoint of health and environment. Given the very low concentrations of Mo in water, it is necessary to use highly sensitive techniques such as ICP-MS or elaborate methods including preconcentration prior to detection. In this work, a new method for the determination of molybdenum in groundwater was developed, incorporating a preconcentration step based on dispersive liquid–liquid microextraction (DLLME) prior to detection by electrothermal atomic absorption spectrometry (ETAAS). After the injection of a ternary mixture formed by an aqueous solution of the complexing agent (potassium ethyl xanthate) and extraction and dispersion solvents (carbon tetrachloride, acetonitrile), the formation of the Mo–xanthate complex occurs followed by its extraction in fine droplets of carbon tetrachloride. After separating the phases the molybdenum content is measured by ETAAS. Several experimental parameters were optimised and the method was validated, presenting a detection limit (3s/b) of 0.017 μg L⁻¹, a quantification limit (10s/b) of 0.062 μg L⁻¹, and an enrichment factor of 165 for a sample volume of 6.0 mL. The calibration curve was linear in the range of 0.06–1.1 μg L⁻¹, the precision (repeatability, s_r (%), n = 10) was 2.98% at 0.1 μg L⁻¹ and the recovery of spiked samples was 98.5–103%. This method was successfully applied to the determination of molybdenum in groundwater and the results were found to be equivalent to those obtained by ICP-MS.