Extraction and high-performance liquid chromatographic analysis of C60, C70, and [6,6]-phenyl C61-butyric acid methyl ester in synthetic and natural waters
Introduction
The development, production, and use of nanomaterials are expected to grow rapidly over the next decade. It is estimated that there are currently close to 500 consumer products on the market that contain nanoscale materials [1]. Recognizing the need for further research on the environmental and human health effects of nanomaterials, the United States federal departments and agencies that participate in the National Nanotechnology Initiative, with input from industry liaison groups, produced a report identifying the key environmental, health, and safety research needs for engineered nanomaterials [2]. Some of the key research needs identified in this report were the development of sampling and analytical methodologies for nanomaterials in environmental matrices.
Fullerenes as a class of nanomaterials were selected for this study because of their growing use in commercial products: the Woodrow Wilson International Center for Scholar's Project on Emerging Nanotechnologies database indicates that fullerenes and other carbon-based nanomaterials use in consumer products is second only to that of nano-sized silver [1]. In addition, fullerenes were studied due to their unique colloidal properties in water which can affect both their behavior in the environment as well as their partitioning behavior in the extraction process in ways not predictable solely by their molecular solubilities. Therefore, the goal of this work was to develop analytical methodologies for extracting and quantifying fullerenes from aqueous colloidal suspensions that are representative of the type of suspensions that could form in the environment as the industrial and consumer use of these materials increases.
Studies have indicated that C60 can form stable colloidal suspensions in water when C60 is introduced to the aqueous phase through solvent exchange, sonication, extended mixing, or some combination of these techniques [3], [4], [5]. Most studies to date have utilized the solvent exchange technique; however, the solvents used may themselves be retained in the cluster structure of C60 aggregates, which may influence the surface properties of the colloidal suspension [3]. Extended mixing with water without the aid of any organic solvents, the technique used in this study, produces colloidal fullerene suspensions which are more representative of the type of fullerene suspensions likely to occur in natural waters. All of these techniques for creating fullerene suspensions yield colloidal suspensions with effective aqueous phase concentrations many orders of magnitude above the aqueous solubilities of molecular fullerenes. For C60, aqueous colloidal suspensions with concentrations as high as 235 mg/L have been reported [6], which is 1016 times higher than C60's estimated water solubility [7].
Methods for analysis of aqueous C60 suspensions have been reported [8], [9], [10], [11], as have methods for extraction and analysis of C60 in biological samples [8], [10], [12]; however, quantitative methods for the analysis of C60 and other fullerenes in actual environmental media or under varying solution conditions are scarce [13]. Sampling and analyzing fullerene suspensions pose several challenges. For example, it has been observed that C60 adsorbs to glassware from pure methanol, being essentially 100% adsorbed in 4 h [14]. Also, despite molecular C60's very high solubility in toluene relative to water, C60 will not readily partition into toluene from water when C60 is present as stable colloidal aggregates in aqueous suspension (often referred to as nano-C60) without the presence of an oxidizing agent or salt to disrupt the stability of the colloidal aggregates and enhance C60 partitioning into the toluene phase [8], [9].
Many analytical, and most environmental, studies on fullerenes in aqueous suspensions have focused on the analysis and colloidal properties of C60. For this study, three fullerenes, C60, C70, and PCBM ([6,6]-phenyl C61-butyric acid methyl ester) were selected for investigation. Specifically, C60 and C70 fullerenes were selected because they are common constituents in commercial fullerene mixtures – additionally, C60 was selected as it is a common impurity in nanotube formulations and to allow for comparison to prior studies. The C60 fullerene derivative PCBM was selected as it has been used in many nanomaterial research and engineering applications, particularly in polymer electronic applications where PCBM is the most commonly used n-type semiconductor in organic photovoltaics [15], [16]. Since pH and ionic strength are often the primary solution chemistry properties governing colloid size and surface charge in aqueous media, this study examined the extractability and analysis of fullerenes from aqueous suspensions at varying pH and ionic strengths using laboratory prepared background solutions. In addition, fullerene suspensions were also extracted and analyzed from ground water and from surface water collected from a small first-order stream (a perennial stream without any perennial tributaries).
Section snippets
Chemicals and materials
The C60 (purity 99.9%) and C70 (purity 99.0%) fullerenes were purchased from MER Corp. (Tucson, AZ, USA) and the PCBM (purity 99.5%) from MTR Ltd. (Cleveland, OH, USA). All fullerenes were used as received from the manufacturers. All chemical reagents used, Mg (ClO4)2, NaCl, HEPES, TRIS, and sodium acetate were reagent grade with purity ≥99%. The toluene, methanol, and acetonitrile used were HPLC grade and were filtered through a 0.45 μm nylon filter prior to use. All double deionized (DDI)
HPLC-UV analysis
The low water solubility of most fullerenes necessitates the use of a relatively low polarity mobile phase, here 80% toluene and 20% acetonitrile by volume, so the chromatographic system used in this study is nominally reverse-phase, rather than classic reverse-phase. Analysts need to be aware of this difference as this non-aqueous mobile phase may not be compatible with standard reverse-phase seals and other HPLC components. As depicted in the fullerenes standard chromatogram in Fig. 1a, all
Acknowledgements
Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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2017, Liquid Chromatography: Applications: Second EditionCharacterisation and determination of fullerenes: A critical review
2015, Analytica Chimica ActaCitation Excerpt :LLE [109,117,120] and solid phase extraction (SPE) [141,153] are the methods most commonly used for the extraction of fullerenes from environmental waters. In LLE, salts are currently added to destabilize the aqueous nC60 aggregates and facilitate its transfer into the organic solvent [109,120]. In general, LLE provides higher recoveries than SPE (Table 4) and it can be applied to a wider range of water samples.
Analysis of C<inf>60</inf>-fullerene derivatives and pristine fullerenes in environmental samples by ultrahigh performance liquid chromatography-atmospheric pressure photoionization-mass spectrometry
2014, Journal of Chromatography ACitation Excerpt :Among the analytical methods reported in the literature for fullerene determination in environmental samples [17–20], liquid chromatography–mass spectrometry (LC–MS) is the method of choice for the quantification of low concentrations of fullerenes, and the use of MS analyzers of both low [21] and high resolution [22,23], has been described. Regarding ionization sources, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the most frequently used [21,24–27] although lately, atmospheric pressure photoionization (APPI) has been proposed for the analysis of fullerenes in water samples [27–29]. Most of the reported studies focus on the analysis of pristine fullerenes, especially C60 and C70 [18,21,22,28–30] and only few studies describe analytical methodologies for some functionalized fullerenes [21,23,31].