Spectrophotometric determination of trace-amount tungsten in environmental and biological samples via...

A new, accurate, and selective process has been established for the extraction, preconcentration, and detection of tungsten (W⁶⁺) ions in water, alloys, and biological matrices. This technique employs ionic liquid-based ultrasound-assisted dispersive liquid-liquid microextraction, followed by the spectrophotometric measurement of a characteristic deep-red color. For the first time, the compound 4-(2-hydroxy-4-nitroazobenzene)-2-methyl quinolone (HNABMQ) was utilized as a tungsten-selective chelating agent. Extraction was performed in an ultrasonic bath at 25 °C ± 2.0 °C using HNABMQ, together with the ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Omim][TF₂N]). After centrifugation, the W⁶⁺ complex was concentrated within the ionic liquid droplets, and 200 µL of acetonitrile was subsequently added to the ionic liquid-enriched layer before conducting spectrophotometric measurements. The main factors determining the recovery of the W⁶⁺ ions were thoroughly evaluated and optimized to attain the best performance. Following the adjustment of both the experimental and instrumental parameters, the approach showed a detection limit of 2.9 ng mL^-1 and a quantification limit of 9.7 ng mL^-1. A preconcentration factor of 1200 was attained, with a linear calibration range extending from 10 to 280 ng mL^-1. At a W⁶⁺ concentration of 150 ng mL^-1 (n = 10), the relative standard deviation (RSD) was determined to be 2.3%. Validation studies confirm that this technique provides a rapid, straightforward, and effective means of quantifying W⁶⁺ ions across a range of sample types, including water, alloys, and biological specimens, with the added benefit of requiring only minimal solvent volumes.