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Speciation Analysis of Silver Nanoparticles and Silver Ions in Antibacterial Products and Environmental Waters via Cloud Point Extraction-Based Separation Jing-bo Chao,†,‡ Jing-fu Liu,*,† Su-juan Yu,† Ying-di Feng,† Zhi-qiang Tan,† Rui Liu,† and Yong-guang Yin† †
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China ‡ Chemical Metrology and Analytical Science Division, National Institute of Metrology, P. R. China, Beijing 100013 ABSTRACT: The rapid growth in commercial use of silver nanoparticles (AgNPs) will inevitably increase silver exposure in the environment and the general population. As the fate and toxic effects of AgNPs is related to the Ag+ released from AgNPs and the transformation of Ag+ into AgNPs, it is of great importance to develop methods for speciation analysis of AgNPs and Ag+. This study reports the use of Triton X-114based cloud point extraction as an efficient separation approach for the speciation analysis of AgNPs and Ag+ in antibacterial products and environmental waters. AgNPs were quantified by determining the Ag content in the Triton X-114-rich phase with inductively coupled plasma mass spectrometry (ICPMS) after microwave digestion. The concentration of total Ag+, which consists of the AgNP adsorbed, the matrix associated, and the freely dissolved, was obtained by subtracting the AgNP content from the total silver content that was determined by ICPMS after digestion. The limits of quantification (S/N = 10) for antibacterial products were 0.4 μg/kg and 0.2 μg/kg for AgNPs and total silver, respectively. The reliable quantification limit was 3 μg/kg for total Ag+. The presence of Ag+ at concentrations up to 2-fold that of AgNPs caused no effects on the determination of AgNPs. In the cloud point extraction of AgNPs in antibacterial products, the spiked recoveries of AgNPs were in the range of 71.7103% while the extraction efficiencies of Ag+ were in the range of 1.210%. The possible coextracted other silver containing nanoparticles in the cloud point extraction of AgNPs were distinguished by transmission electron microscopy (TEM), scanning electron microscopy (SEM)- energy dispersive spectroscopy (EDS), and UVvis spectrum. Real sample analysis indicated that even though the manufacturers claimed nanosilver products, AgNPs were detected only in three of the six tested antibacterial products.
W
ith the development of nanotechnology, there is a growing production and application of silver nanoparticles (AgNPs) in various areas.14 It is reported that about 320 tons/year of AgNPs are produced and used wordwide,5 and about 30% of the over 800 nanomaterial-containing consumer products are claimed to have AgNPs.2 Application areas of AgNPs included consumer products, food technology, textiles/fabrics, as well as medical products and devices.24 As examples, AgNPs are widely used for medical prosthetics such as treatment of skin disease, particularly for the burns and various ulcers (e.g., wound dressing) and toxic epidermal necrolysis, as well as used to coat implantable medical devices such as endoscopes, urological stents, infusion ports, and surgical or dental instruments.6,7 The rapid growth in the commercial use of AgNPs will inevitably increase silver exposure to the general population.2 AgNPs may penetrate the skin8 via textile or wound dressing contact, be inhaled from some spray medicine, or ingress into the female genital tract by incorporation into female hygienic products or medical implants.9 In vitro studies showed that AgNPs were toxic to rat and human cells.1014 It was also reported that AgNPs released from medical devices can form r 2011 American Chemical Society
proteinsilver complexes deposited in the liver, kidney, lung, and other organs.15 The production, use, and disposal of AgNPs-containing products can lead to the release of increased amounts of silver into various environmental compartments, where the impacts of AgNPs and Ag+ to organisms and human beings remains to be explored. Although AgNPs were toxic to both aerobic and anaerobic bacteria separated from wastewater treatment plants (WWTP),16 the latest studies showed that AgNPs are ready to transform in environmental wastewater into silver sulfide that has been shown to have minimal potential for impact on the biological processes at the WWTP.17,18 In addition, even though high loadings of AgNPs by wound dressing caused localized argyria and increased levels of silver in the liver, these two symptoms were reversible once the treatment was removed.19 On the other hand, a latest study has shown the transformation of Ag+ into AgNPs by the reduction of Ag+ by humic acids at room Received: April 28, 2011 Accepted: July 26, 2011 Published: July 28, 2011 6875
dx.doi.org/10.1021/ac201086a | Anal. Chem. 2011, 83, 6875–6882
Analytical Chemistry temperature.20 This transformation of Ag+ to AgNPs has major consequences to the interpretation of AgNP fates as potentially any source of silver (both conventional or nano) can lead to the formation of environmental AgNPs. The mechanism of toxic properties of AgNPs has not been clearly elucidated. It is generally believed that the toxicity of AgNPs is related to its release of Ag+.2,2124 For instance, the activity of the AgNPs against the test organism disappeared when cysteine was added into the system to scavenge silver ions.24 However, the AgNP effects are not due simply to the release of Ag+ into the surrounding environment, as the AgNP effects are distinct from those of Ag+ alone and depend on size and coating.12,16,2428 To assess the risk of exposure and further understand the AgNP effects, information on the concentration, size, and form (aggregates, agglomerates) of AgNPs, as well as the Ag+ concentration is urgently needed.2,3 Given the release of Ag+ from AgNPs and the transformation of Ag+ into AgNPs in the environment,20 Ag+ and AgNPs are commonly coexisted and it is of great importance to develop methods for speciation analysis of AgNPs and Ag+.29,30 Methods for the separation, identification, characterization, and quantification of nanomaterials in consumer products, foods, and environmental samples are limited.3141 In the case of AgNPs, the identification was usually conducted by the combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and UVvis spectrum,24,4247 whereas the quantification was performed after oxidation of AgNPs to Ag+ and detection with inductively coupled plasma mass spectrometry (ICPMS),24,46,47 graphite furnace atomic absorption spectrometry,30,48 inductively coupled plasma optical emission spectrometer (ICPOES),42,44,49,50 or chromogenic method.5153 AgNPs in sanitizer gel and fabric were determined by a rhodamine-based fluorogenic and chromogenic probe after oxidation of AgNPs to Ag+ with hydrogen peroxide.51 Very recently, the total silver content in AgNP-containing consumer products used in the home were quantified with ICP-OES after subjection to nitric acid digestion.44 These above procedures are incapable of distinguishing the ionic form and the nanoparticle form of silver, and the authors address that the detection methods specific to AgNPs are needed.44 The speciation analysis of AgNPs and Ag+ relies on their separation, on which a few strategies have been reported. One approach for the quantification of AgNPs is based on the difference between the total Ag concentration and the free Ag+ concentration. Namely, the total Ag concentration was determined by ICPMS24 or ICP-OES42,44,50 after sample digestion, whereas the free Ag+ concentration was detected before digestion using a silver selective electrode,24,42,50 after separation with centrifugal ultrafiltration42 or dialysis,48 or by sampling with diffusive gradients in thin films (DGT).24 In another report,45 soil suspensions were treated with a 0.45 μm microfiltration membrane and 1 kDa ultrafiltration membrane in sequence. The Ag fraction of
