Separation of silver and gold ions/nanoparticles in water using chemically modified-silica for spectrometric detection

Abstract

The separation of gold and silver ions/nanoparticles in water using chemically-modified silica and unmodified silica was investigated by solid-phase extraction (SPE) followed by the determination via inductively coupled plasma-optical emission spectrometry (ICP-OES). 1-Carboxymethyl-3-methylimidazolium chloride ionic liquid [MimCM]Cl and humic acid (HA) immobilized onto aminopropyl silica (SiAP) sorbents were successfully prepared for the separation of metal species. Ionic liquid modified-SiAP (SiAP-IL) sorbent was chosen for the separation of gold ions/nanoparticles, while humic acids modified-SiAP (SiAP-HA) sorbent was selected for silver ions/nanoparticles. Based on this proposed method, the metal ions were preferentially adsorbed onto the solid sorbent over the metal nanoparticles, thus the metal nanoparticles were retained and observed in solution. The pH of solution, extraction time and types of eluent were optimized. The separation of metal species was observed at pH 3 for all adsorbents. The optimal extraction time of gold ions/nanoparticles was achieved within 5 minutes whereas a good separation of silver ions/nanoparticles was observed within 15 minutes. The higher elution efficiency of thiourea was observed for SiAP-IL and sequential elution of SiAP sorbent. Meanwhile, nitric acid showed high elution efficiency for SiAP-HA sorbent. Under the optimum conditions, the proposed method was successfully applied for the separation and determination of gold and silver species in household products and wastewater samples using ICP-OES. The recoveries of gold and silver ions/nanoparticles were higher than 80%. The overall %RSD are lower than 3. The detection limit (LOD) was 5.77 and 4.61 µg L-1 for gold and silver, respectively, using ICP-OES.