Determination of ultra-trace gold in cosmetics using aluminum-magnesium layered double hydroxide/graphene oxide nanocomposite

A new solid-phase microextraction method for preconcentration and determination of ultra-trace Au(III) and AuNPs was developed. For this purpose, a nanosized aluminum-magnesium layered double hydroxide (AlMg-LDH)/graphene oxide (GO) nanocomposite was synthesized. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy confirmed the successful synthesis of the nanocomposite AlMg-LDH/GO with a well-crystallized hexagonal structure. The synthesized nanomaterial allows sorption with 100% recovery of AuNPs at pH 1-5 or AuNPs and Au(III) ions at pH 1-2. Therefore, gold ions and corresponding gold nanoparticles can be together or separately determined. The maximum sorption capacity of the nanocomposite is 12 mg g-1 for Au(III). After adsorption, gold was directly determined on the AlMg-LDH/GO by energy-dispersive X-ray fluorescence spectrometry with a detection limit of 0.06 ng mL-1, precision ca. 4%, and recovery >90%. According to the Green Chemistry rule, the method has significant advantages, such as reducing the amount of sorbent required and eliminating solvent. The elution of analytes from the nanosorbent is completely eliminated in the developed method. The developed method was successfully used to extract and determine ultra-trace gold in cosmetics products.