Field-flow fractionation of nano- and microparticles in rotating coiled columns

Nanoparticles of dust as an emerging contaminant in urban environments

Due to very high mobility in the environment and penetration ability into living organisms, nanoparticles (NPs) of urban dust pose a potential threat to human health and urban ecosystems. Currently, data on the chemical composition of NPs of urban dust, their fate in the environment, and corresponding risks are rather limited. In the present work, NPs of deposited urban dust have been comprehensively studied for the first time; NPs isolated from 78 samples of dust collected in Moscow, the largest megacity in Europe, being taken as example. The elemental composition, potential sources as well as environmental, ecological, and health risks of NPs of urban dust are assessed. It is found that dust NPs are extremely enriched by Cu, Hg, Zn, Mo, Sb, and Pb, and can serve as their carrier in urban environments. No regularities in the spatial distribution of elements have been found, probably, due to high mobility of dust NPs. High ecological and health risks caused by dust NPs are demonstrated. Source apportionment study has evaluated one natural and two anthropogenic sources of elements in NPs of urban dust; the contribution of natural and anthropogenic sources being comparable. It is also shown that dust NPs may be considered as an important carrier of trace elements in urban aquatic systems. Additionally, the risks associated with NPs and bulk samples of dust have been compared. The observed risks associated with NPs are significantly higher.

Novel zone elution mode in coiled tube field-flow fractionation for online separation and characterization of environmental submicron particles

Coiled tube field-flow fractionation (CTFFF) is currently applied to environmental and material studies. In the present work, a novel zone elution mode in CTFFF has been proposed and developed. Zone elution mode is based on the separation of particles by stepwise decreasing the flow rate of the carrier fluid and their subsequent elution at a constant flow rate. The fractionation parameters were optimized using a mixture of standard silica submicron particles (150, 390, and 900 nm). Taking samples of volcanic ash as examples, it has been demonstrated that zone elution mode can be successfully used for the fractionation of environmental nano- and submicron particles. For the first time, CTFFF was coupled online with a dynamic light scattering detector for the size characterization of eluted particles. Zone elution in CTFFF can serve for the further development of hyphenated techniques enabling efficient fractionation and size/elemental characterization of environmental particles in nano- and submicrometric size ranges.

Using the forces of hydrodynamic countercurrent chromatography for the study of bacteriophages

Bacteriophages (phages) are viruses that target bacteria, with the ability to lyse and kill host bacterial cells. Due to this, they have been of some interest as a therapeutic since their discovery in the early 1900s, but with the recent increase in antibiotic resistance, phages have seen a resurgence in attention. Current methods of isolation and purification of phages can be long and tedious, with caesium chloride concentration gradients the gold standard for purifying a phage fraction. Isolation of novel phages requires centrifugation and ultrafiltration of mixed samples, such as water sources, effluent or faecal samples etc, to prepare phage filtrates for further testing. We propose countercurrent chromatography as a novel and alternative approach to use when studying phages, as a scalable and high-yield method for obtaining phage fractions. However, the full extent of the usefulness and resolution of separation with this technique has not been researched; it requires optimization and ample testing before this can be revealed. Here we present an initial study to determine survivability of two phages, T4 and ϕX174, using only water as a mobile phase in a Spectrum Series 20 HPCCC. Both phages were found to remain active once eluted from the column. Phages do not fully elute from the column and sodium hydroxide is necessary to flush the column between runs to deactivate remaining phages.

Field-flow fractionation for nanoparticle characterization

This review presents field-flow fractionation: The elements of theory enable the link between the retention and the characteristics of the nanometer-sized analytes to be highlighted. In particular, the nature of force and its way of being applied are discussed. Four types of forces which determine four types of techniques were considered: hydrodynamic, sedimentation, thermal, and electrical; this is to show the importance of the choice of technique in relation to the characterization objectives. Then the separation performance is presented and compared with other separation techniques: field-flow fractionation has the greatest intrinsic separation capability. The characterization strategies are presented and discussed; on the one hand with respect to the characteristics needed for the description of nanoparticles; on the other hand in connection with the choice of the nature of the force, and also of the detectors used, online or offline. The discussion is based on a selection of published study examples. Finally, current needs and challenges are addressed, and as response, trends and possible characterization solutions.

Natural silicate nanoparticles: separation, characterization, and assessment of stability and perspectives of their use as reference nanomaterials

Natural nanomaterials, which play a very important role in environmental processes, are so far poorly studied. Firstly, the separation of nanoparticles from the bulk sample is a challenge. Secondly, the absence of reference natural nanomaterials makes it impossible to compare the results obtained by different researchers and develop a unified methodology for the separation and characterization of natural nanomaterials. Therefore, the development of reference natural nanomaterials is an urgent need of the environmental analytical chemistry. In this work, mineral nanoparticles (kaolinite, montmorillonite, muscovite, and quartz) have been studied as potential reference natural nanomaterials. A set of analytical methods including coiled-tube field-flow fractionation, scanning electron microscopy, dynamic light scattering, laser diffraction, inductively coupled plasma atomic emission, and mass spectrometry are applied to the separation and characterization of nanoparticles. It has been shown by laser diffraction that 93-98% of separated mineral nanoparticles are in the size range from about 40 to 300 nm, while 2-7% have size up to 830 nm. The size range of particles is confirmed by electron microscopy. Major (Al, Na, K, Ca, Fe), trace (Ti, Co, Cu, Zn, Tl, Pb, Bi, etc.), and rare earth elements have been determined in the suspensions of kaolinite, montmorillonite, and muscovite nanoparticles. Based on Al content, the concentration of mineral nanoparticles in suspensions is estimated. Agglomeration stability (consistency of size distribution) of nanoparticles at pH 6-8 is assessed. It has been shown that muscovite nanoparticles are stable at pH 7-8, whereas montmorillonite nanoparticles are stable only at pH 8 for at least 4 weeks. A noticeable agglomeration of kaolinite nanoparticles is observed at pH 6-8. Due to the low concentration of quartz nanoparticles, their characterization and stability assessment are hindered. The challenges of the development of reference natural nanomaterials are discussed.

On-line determination of soluble Zn content and size of the residual fraction in PM2.5 incubated in various aqueous media

Transition metals in airborne particulate matter, especially those with aerodynamic diameters no more than 2.5 μm (PM_2.5), have attracted considerable attention due to their potential environmental and human health risks. However, determination of these potential risks requires comprehensive knowledge of their dissolution behavior and residual size in aqueous media. Herein, we describe an analytical method for on-line determination of the soluble fraction of Zn as a model transition metal and the size of residual PM_2.5 using hollow fiber flow field-flow fractionation (HF5) coupled with UV-vis absorption spectroscopy and inductively coupled plasma optical emission spectroscopy. HF5 was directly applied on the incubated samples in pure water (PW), simulated natural water (SNW), and simulated lung fluid (SLF) due to its efficient in-line filtration and excellent fractionation resolution. Firstly, the potential of the proposed method (under optimized conditions) for size characterization was assessed against commercial silica microparticles, and results in good agreement with manufacturer and scanning electron microscopy values were obtained. The accuracy of quantification of soluble Zn in various media was then validated using a standard reference material in terms of satisfactory recoveries compared with the reference values. For the real PM_2.5 samples collected from different sites in Beijing, China, the soluble Zn percentages in PW, SNW, and SLF were within 15.4-16.7%, 10.6-12.7%, and 43.1-46.9%, respectively, with the amount of particles smaller than ~10 nm released from PM_2.5 increasing in the order of SNW < PW < SLF. The proposed HF5-based method provides a powerful and efficient tool for the quantification of soluble transition metal fractions and size characterization of residual particles with reduced analysis times, thus possessing great promise in real-time tracking of the transformation of PM_2.5 in environmental and physiological media and in risk assessment.

Separation of nanoparticles from polydisperse environmental samples: comparative study of filtration, sedimentation, and coiled tube field-flow fractionation

Nanoparticles (NPs) in the environment have a potential risk for human health and the ecosystem due to their ubiquity, specific characteristics, and properties (extreme mobility in the environment, abilities to accumulate of toxic elements and penetrate into living organisms). There is still a gap in studies on the chemical composition of natural NPs. The main reason is the difficulty to recover NPs, which may represent only one-thousandth or less of the bulk environmental sample, for further dimensional and quantitative characterization. In the present study, a methodology for the recovery of the nanoparticle fraction from polydisperse environmental samples was developed taking as example volcanic ashes from different regions of the world. For the first time, three separation methods, namely, filtration through a 0.45-μm membrane, sedimentation, and coiled tube field-flow fractionation (CTFFF), were comparatively studied. The separated fractions were characterized by laser diffraction and scanning electron microscopy and then analyzed by inductively coupled plasma atomic emission and mass spectrometry. It has been shown that all three methods provide the separation of NPs less than 400 nm from the bulk material. However, the fraction separated by sedimentation also contained a population (5% in mass) of submicron particles (~ 400-900 nm). The filtration resulted in low recovery of NPs. The determination of most trace elements was then impossible; the concentration of elements was under the limit of detection of the analytical instrument. The sedimentation and CTFFF made it possible to determine quantifiable concentrations for both major and trace elements in separated fractions. However, the sedimentation took 48 h while CTFFF enabled the fractionation time to be decreased down to 2 h. Hence, CTFFF looked to be the most promising method for the separation of NPs followed by their quantitative elemental analysis.

A contribution of nanoscale particles of road-deposited sediments to the pollution of urban runoff by heavy metals

Road-deposited sediments (RDS) present a sink for traffic-related pollutants including heavy metals (HMs). HMs associated with RDS particles enter the urban aquatic environment during rainfall events and have adverse effects for biota. RDS nanoscale particles (NSPs) require special consideration due to their specific properties, extremely high mobility in the environment, and ability to penetrate into living organisms. In the present work, the contribution of NSPs of RDS to the pollution of urban runoff by HMs has been evaluated for the first time. It has been shown that bulk RDS samples are polluted by HMs as compared to background urban soils (geo-accumulation indexes of Cu and Zn may attain 2-3). Meanwhile, NSPs of RDS are enriched by HMs as compared to bulk samples; concentration factor for Ni, Cu, Zn, Cd, Sn, and Pb in NSPs being varied from 2 to 10. The water-soluble fractions of RDS samples were also analyzed. Results have shown that the content of water-soluble HMs in RDS is insignificant and rarely exceeds 0.5% of the total contents of HMs in the bulk samples; the highest contents are identified for Cu and Pb. It should be noted that the water-soluble fraction is nearly free from Zn and this element is almost entirely present as particulate matter (NSPs). In general, the overall contribution of NSPs and water-soluble fraction of HMs to the pollution of urban runoff is comparable.

Assessment of elemental composition and properties of copper smelter-affected dust and its nano- and micron size fractions

A comprehensive approach has been developed to the assessment of composition and properties of atmospherically deposited dust in the area affected by a copper smelter. The approach is based on the analysis of initial dust samples, dynamic leaching of water soluble fractions in a rotating coiled column (RCC) followed by the determination of recovered elements and characterization of size, morphology and elemental composition of nano-, submicron, and micron particles of dust separated using field-flow fractionation in a RCC. Three separated size fractions of dust (<0.2, 0.2-2, and >2 μm) were characterized by static light scattering and scanning electron microscopy, whereupon the fractions were analyzed by ICP-AES and ICP-MS (after digestion). It has been evaluated that toxic elements, which are characteristics for copper smelter emissions (As, Cu, Zn), are accumulated in fraction >2 μm. At the same time, up to 2.4, 3.1, 8.2, 6.7 g/kg of As, Cu, Zn, Pb, correspondently, were found in nanoparticles (<0.2 μm). It has been also shown that some trace elements (Sn, Sb, Ag, Bi, and Tl) are accumulated in fraction <0.2, and their content in this fraction may be one order of magnitude higher than that in the fraction >2 μm, or the bulk sample. It may be assumed that Sn, Sb, Ag, Bi, Tl compounds are adsorbed onto the finest dust particles as compared to As, Cu, Zn compounds, which are directly emitted from the copper smelter as microparticles.

The 8th International Conference on Counter-current Chromatography held at Brunel University, London, UK, July 23-25, 2014

The 8th International Conference on Counter-current Chromatography (CCC2014) was held at Brunel University London from July 23rd to 25th, 2014. It has been 14 years since Brunel hosted the first International Conference on CCC (CCC2000) at the beginning of the millennium and therefore, it was a good opportunity to review the progress of this emerging technology and particularly the impact it is having with industry today.