Article pubs.acs.org/ac
Quantitative Characterization of Gold Nanoparticles by Coupling Thin Layer Chromatography with Laser Ablation Inductively Coupled Plasma Mass Spectrometry Neng Yan,† Zhenli Zhu,*,† Lanlan Jin,† Wei Guo,† Yiqun Gan,§ and Shenghong Hu†,‡ †
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China, 430074 Faculty of Earth Sciences, China University of Geosciences, Wuhan, China, 430074 § School of Environmental Studies, China University of Geosciences, Wuhan, China, 430074 ‡
S Supporting Information *
ABSTRACT: Metal nanoparticles (NPs) determination has recently attracted considerable attention because of the continuing boom of nanotechnology. In this study, a novel method for separation and quantitative characterization of NPs in aqueous suspension was established by coupling thin layer chromatography (TLC) with laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Gold nanoparticles (AuNPs) of various sizes were used as the model system. It was demonstrated that TLC not only allowed separation of gold nanoparticles from ionic gold species by using acetyl acetone/butyl alcohol/triethylamine (6:3:1, v/v) as the mobile phase, but it also achieved the separation of differently sized gold nanoparticles (13, 34, and 47 nm) by using phosphate buffer (0.2 M, pH = 6.8), Triton X-114 (0.4%, w/v), and EDTA (10 mM) as the mobile phase. Various experimental parameters that affecting TLC separation of AuNPs, such as the pH of the phosphate buffer, the coating of AuNPs, the concentrations of EDTA and Triton X-114, were investigated and optimized. It was found that separations of AuNPs by TLC displayed size dependent retention behavior with good reproducibility, and the retardation factors (Rf value) increased linearly with decreasing nanoparticle size. The analytical performance of the present method was evaluated under optimized conditions. The limits of detection were in the tens of pg range, and repeatability (RSD, n = 7) was 6.3%, 5.9%, and 8.3% for 30 ng of 13 nm AuNPs, 34 nm AuNPs, and 47 nm AuNPs, respectively. The developed TLC-LA-ICP-MS method has also been applied to the analysis of spiked AuNPs in lake water, river water, and tap water samples.
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anoparticles (NPs), especially metal nanoparticles (M-NPs) are used increasingly in various areas due to their unique properties. For example, AuNPs are widely used in © XXXX American Chemical Society
Received: February 13, 2015 Accepted: May 25, 2015
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DOI: 10.1021/acs.analchem.5b00612 Anal. Chem. XXXX, XXX, XXX−XXX
Article
Analytical Chemistry biomedical imaging,1,2 cancer therapy and diagnostics,3,4 and biological and chemical sensing.4,5 For these applications, physical size, shape, and elemental composition are highly important properties that influence the performance of these NPs, and thus it is critical to prepare nanoparticles with the lowest size and shape dispersion.6 Furthermore, the increasing use of M-NPs will inevitably result in their widespread release into the environment.7 Therefore, in addition to the beneficial use of NPs, concerns about adverse effects regarding their release, toxicity and pathways in the environment have also been raised. Several studies have demonstrated that the concentration, size, and form of M-NPs, as well as their corresponding metal ions concentrations impact their toxicity.8 Moreover, many studies have reported that nanoparticles possess higher toxicities in comparison with metal ions of the same element.9 Therefore, it is of considerable interest to develop new methods for the size characterization and quantification of metal nanoparticles and their corresponding metal ions.10 Various analytical approaches for the characterization of M-NPs (size distribution, elemental composition and quantification etc.) have been developed. Microscopy/microscopyrelated techniques (e.g., scanning/transmission electron microscopy (SEM/TEM),11,12 atomic force microscopy (AFM)13 and dynamic light scattering (DLS)12,14 are commonly used to obtain the size distribution and structural information on the NPs. Although elemental analysis of the NPs could be performed when such instrumentation is equipped with energy dispersive X-ray spectroscopy detectors (EDX),15 the elemental characterization of NPs and their quantification are mainly achieved by coupling of different separation/enrichment techniques with element-sensitive detectors (e.g., inductively coupled plasma mass spectrometry (ICP-MS)).16 In recent years, filtration/ultrafiltration,17,18 ultracentrifugation,12,19 and extraction based methods have been widely used for the separation and quantification of NPs and their corresponding metal ions. Among these various techniques, extraction based methods have received increasing attention as they allow effective separation and preconcentration of the NPs with no changes in the size and shape of the NPs, and thus could be used in the determination of NPs at low concentration. Several extraction methods including liquid−liquid extraction,20 cloud point extraction(CPE),21,22 solid-phase extraction (SPE),23,24 monolithic capillary microextraction (CME),25 and ligandassisted extraction26 have been reported for the quantification of AuNPs,27,28 AgNPs,21,27,29 ZnO NPs,30 CuO NPs,31 etc. However, extraction based methods are usually used only for determination of the NP and metal ion speciation while size distribution information on NPs is difficult to obtain from these approaches. In addition, extraction based methods are usually tedious and time-consuming.24 The use of single particle (SP)ICP-MS has recently been demonstrated as a promising method for the detection and characterization of low concentrations of M-NPs due to its ability to provide particle size distributions and particle number concentrations simultaneously.32−35 However, it could not be used for smaller size particles since its current minimum detectable particle size are in the range of 10−20 nm depending on the species of interest. Chromatographic techniques including size-exclusion chromatography (SEC),36 capillary electrophoresis (CE),37,38 gel electrophoresis (GE), 39 hydrodynamic chromatography (HDC),7,34 liquid chromatography (LC),40 high performance liquid chromatography (HPLC)41 and field-flow fractionation (FFF)42,43 coupled with ICP-MS provide a powerful approach
for size-fractionated analyses of NPs.44−46 SEC is commonly used to acquire the shape and size distribution information on NPs smaller than 100 nm due to its good separation efficiency, fast operation and reliability. However, inherent problems such as degradation or losses by irreversible adsorption to the stationary phase exist in SEC, although it may be minimized by addition of sodium dodecyl sulfate (SDS).39 HDC, which is suitable for sizing NPs within the range of 5 to 300 nm, provides another selective and sensitive analytical tool for the separation of NPs.34,47 It has a short analysis time (typically
