Ultrasound-assisted ionic liquid microextraction and colorimetric analysis for trace-level gold detection in environmental and geological samples

Abstract

A novel, precise, and targeted method has been developed for isolating, preconcentrating, and analyzing gold ions in water, ore, and food samples. This approach utilizes ultrasound-assisted dispersive liquid–liquid microextraction based on ionic liquids, combined with colorimetric detection of a distinct deep red hue. The compound 2-amino-4-(m-tolylazo)pyridine-3-ol (ATAP), introduced for the first time as a gold-specific chelating agent, was employed alongside the ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in an ultrasonic bath maintained at 25 ± 2 °C for extraction. Following centrifugation, the gold complex was enriched within the ionic liquid droplets, and 200 μL of ethanol was added to the ionic liquid-rich layer prior to colorimetric analysis. Key variables influencing the recovery of Au³⁺ ions were systematically examined and fine-tuned to achieve optimal results. After fine-tuning both the instrumental and experimental conditions, the proposed method demonstrated a linear dynamic range for Au³⁺ ions between 4.0 and 240 ng mL⁻¹, with high molar absorptivity and a Sandell sensitivity of 1.22 × 10⁶ L mol⁻¹ cm⁻¹ and 0.016 ng cm⁻², respectively. The method achieved quantification and detection limits of 3.92 and 1.30 ng mL⁻¹, respectively. A preconcentration factor of 500 was obtained. The relative standard deviation (RSD) was calculated to be 1.89% for gold ions at a concentration of 100 ng mL⁻¹ (n = 10). No significant interference from various anions and cations was detected during the assessment of Au³⁺. These findings confirm that the proposed technique is a fast, straight-forward, highly sensitive, selective, and effective analytical approach for isolating and quantifying Au³⁺ ions in environmental and geological samples, all while using minimal solvent volumes.