Sensitive determination of trace molybdenum in natural waters using dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry

Abstract

A simple, sensitive and rapid method involving dispersive liquid-liquid microextraction was developed for the determination of molybdenum using electrothermal atomic absorption spectrometry. After injection of a ternary mixture containing trichloroethylene (extractor solvent), ethanol (disperser solvent) and ammonium pyrrolidinedithiocarbamate (chelating reagent), the extraction of molybdenum into the aqueous phase occurs. The quantity of the element in the enriched phase was measured using electrothermal atomic absorption spectrometry. Under optimized conditions (pH 2.5, 2.0 mL of disperser solvent, 50 mL of extraction solvent, 50.0 mL of 0.10% m/v chelating solution and centrifugation at 3000 rpm for 2.5 minutes), the method has a detection limit of 0.013 mg L À1 , a quantification limit of 0.044 mg L À1 and an enrichment factor of 75 for a sample volume of 5.0 mL. The certified reference material NIST 2781, Domestic Sludge, was used to assess the accuracy of the method. The proposed procedure was successfully applied to the determination of molybdenum in natural water samples. Experimental InstrumentationAbsorbance measurements were performed using an AAnalyst 400 model atomic absorption spectrometer and an HGA 900 model graphite furnace, both supplied by Perkin Elmer (Shelton, USA). A hollow cathode lamp for molybdenum analysis (Perkin Elmer) was also used. The pH measurements were performed using a Quimis Q400AS pH meter (Diadema, Brazil).

A spectrophotometric method for determination of molybdenum in water samples by using pyrogallol red and a water soluble ionic liquid

“…The limit of detection (LOD) and limit of quantication (LOQ), dened as LOD ¼ 3.3 s m À1 and LOQ ¼ 10 s m À1 where s is the standard deviation of the blank (n ¼ 5) and m is the slope of the calibration graph, were calculated as 0.74 ng mL À1 and 2.47 ng mL À1 , respectively. The sensitivity of the method was found comparable to the other sophisticated instrumental methods coupled with solid phase extraction such as AAS 13 and inductively coupled plasma atomic emission spectroscopy 39 having an LOD level of 1.00 and 0.14 ng mL À1 , respectively. The results of the proposed method were veried with ICP-MS method with an LOD level of 0.02 ng mL À1 .…”

“…A number of techniques such as spectrophotometry, 11 atomic absorption spectroscopy (AAS), 12 and electrothermal atomic absorption spectroscopy 13 have been used to determine Mo(VI) ions in various samples. As an alternative to sophisticated methods, electroanalytical techniques have also been developed for molybdenum ion determination including differential pulse voltammetry, 14 adsorptive stripping voltammetry 15 and, more recently, centri-voltammetry.…”

Monolithic capillary microextraction on-line combined with ICP-MS for determining Ni, Cu and Cd in biological samples

“…Therefore, an appropriate sample pretreatment technique is usually required prior to ICP-MS determination to preconcentrate the target elements and separate the analytes from the matrix for real-world sample analysis. 2 Conventional sample pretreatment techniques, including liquid-liquid extraction (LLE), 7 solid-phase extraction (SPE), 8 cloud point extraction 9 and coprecipitation, 10 have been employed for the separation and preconcentration of trace or ultratrace elements in biological and environmental samples. However, these sample pretreatment techniques have some drawbacks, such as being time consuming, labor intensive, and requiring high sample and reagents consumption; moreover, they are not suitable for analysis of rare and precious biological samples.…”