Ion pair-based dispersive liquid–liquid microextraction for gold determination at ppb level in solid samples after ultrasound-assisted extraction and in waters by electrothermal-atomic absorption spectrometry

A new methodology was developed for the determination of ultratrace levels of gold in water samples, soils and river sediments. Dispersive liquid–liquid microextraction was used to preconcentrate the ion pair formed between AuCl4− and [CH3(CH2)3]4N+ in a microliter-range volume of chlorobenzene using acetone as disperser solvent. When solid samples were analyzed, the method consisted of a combination of ultrasound-assisted extraction and dispersive liquid–liquid microextraction with final detection by electrothermal-atomic absorption spectrometry. Since an HCl medium was required for the formation of the AuCl4− complex, HCl together with HNO3 was used as extractants for ultrasound-assisted extraction. After optimization, the enrichment factor obtained was 220 for water samples. Moreover, the extraction efficiency was around 96%. The repeatability, expressed as relative standard deviation ranged from 3.6% to 9.7%. The instrumental detection limit was 8.4 ng L−1, whereas the procedural detection limits were 42 ng L−1 for water samples and 1.5 ng g−1 for environmental solid samples.