title: Toward a robust analytical method for separating trace levels of nano-materials in natural waters: cloud point extraction of nano-copper(II) oxide.
abstract: Cloud point extraction (CPE) factors, namely Triton X-114 (TX-114) concentration, pH, ionic strength, incubation time, and temperature, were optimized for the separation of nano-sized copper(II) oxide (nCuO) in aqueous matrices. The kinetics of phase transfer was studied using UV-visible spectroscopy. From the highest separation rate, the most favorable conditions were observed with 0.2 % w/v of TX-114, pH = 9.0, ionic strength of 10 mM NaCl, and incubation at 40 °C for 60 min, yielding an extraction efficiency of 89.2 ± 3.9 % and a preconcentration factor of 86. The aggregate size distribution confirmed the formation of very large nCuO-micelle assemblies (11.9 μm) under these conditions. The surface charge of nCuO was also diminished effectively. An extraction efficiency of 91 % was achieved with a mixture of TX-100 and TX-114 containing 30 wt.% of TX-100. Natural organic and particulate matters, represented by humic acid (30 mg/L) and micron-sized silica particles (50 mg/L), respectively, did not significantly reduce the CPE efficiency (<10 %). The recovery of copper(II) ions (20 mg/L) in the presence of humic acid was low (3-10 %). The spiked natural water samples were analyzed either directly or after CPE by inductively coupled plasma mass spectrometry following acid digestion/microwave irradiation. The results indicated the influence of matrix effects and their reduction by CPE. A delay between spiking nCuO and CPE may also influence the recovery of nCuO due to aggregation and dissolution. A detection limit of 0.04 μg Cu/L was achieved for nCuO.
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore.
authors.forename: Seyed Mohammad
authors.initials: SM
authors.lastname: Majedi
authors.forename: Barry C
authors.initials: BC
authors.lastname: Kelly
authors.forename: Hian Kee
authors.initials: HK
authors.lastname: Lee
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000379:methods*; D003300:Copper / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D057446:Hydrodynamics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D057230:Limit of Detection; D008823:Micelles; D049329:Nanostructures / Q000032:analysis*; D017830:Octoxynol; D052638:Particulate Matter / Q000032:analysis; D011092:Polyethylene Glycols / Q000737:chemistry; D013054:Spectrophotometry, Atomic; D055672:Static Electricity; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D006812:Humic Substances; D008823:Micelles; D052638:Particulate Matter; D014874:Water Pollutants, Chemical; D014867:Water; D011092:Polyethylene Glycols; D003300:Copper; D017830:Octoxynol; C010615:Nonidet P-40; C000520:cuprous oxide