Quantification of Methylated Selenium, Sulfur, and Arsenic in the Environment

Biomethylation and volatilization of trace elements may contribute to their redistribution in the environment. However, quantification of volatile, methylated species in the environment is complicated by a lack of straightforward and field-deployable air sampling methods that preserve element speciation. This paper presents a robust and versatile gas trapping method for the simultaneous preconcentration of volatile selenium (Se), sulfur (S), and arsenic (As) species. Using HPLC-HR-ICP-MS and ESI-MS/MS analyses, we demonstrate that volatile Se and S species efficiently transform into specific non-volatile compounds during trapping, which enables the deduction of the original gaseous speciation. With minor adaptations, the presented HPLC-HR-ICP-MS method also allows for the quantification of 13 non-volatile methylated species and oxyanions of Se, S, and As in natural waters. Application of these methods in a peatland indicated that, at the selected sites, fluxes varied between 190–210 ng Se·m-2·d-1, 90–270 ng As·m-2·d-1, and 4–14 µg S·m-2·d-1, and contained at least 70% methylated Se and S species. In the surface water, methylated species were particularly abundant for As (>50% of total As). Our results indicate that methylation plays a significant role in the biogeochemical cycles of these element

Characterization of Silver Nanoparticle Products Using Asymmetric Flow Field Flow Fractionation with a Multidetector Approach - a Comparison to Transmission Electron Microscopy and Batch Dynamic Light Scattering

Due to the already prevalent and increasing use of silver-nanoparticle (Ag-NP) products and the raised concerns in particular for the aquatic environment, analytical techniques for the characterization of such products are of need. However, because Ag-NP products are of different compositions and polydispersities, analysis especially of the size distribution is challenging. In this work, an asymmetric flow field flow fractionation (A4F) multidetector system (UV/vis, light scattering, inductively coupled plasma mass spectrometry - ICPMS), in combination with a method to distinguish and quantify the particle and dissolved Ag fractions (ICPMS after ultracentrifugation), for the characterization of Ag-NP products with different degrees of polydispersities is presented. For validation and to outline benefits and limitations, results obtained from batch dynamic light scattering (batch-DLS) and transmission electron microscopy (TEM) were compared. With the developed method a comprehensive understanding in terms of dissolved Ag and Ag-NP concentration as well as an element selective, mass- and number particle size distribution (PSD) was obtained. In relation to batch-DLS, the reliability of the data was improved significantly. In comparison to TEM, faster measurement times and the ability to determine the samples directly in dispersions are clearly advantageous. The proposed setup shows potential for a rapid- and reliable characterization method of virtually any polydisperse metallic NP dispersion, many of them available on the market already

Application of an asymmetric flow field flow fractionation multi-detector approach for metallic engineered nanoparticle characterization - Prospects and limitations demonstrated on Au nanoparticles

In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system. For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1-50 μg Au L-1 in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle-membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup. Figures of merit were obtained, by comparing the results from the multi detector approach outlined above, with results from batch-DLS and transmission electron microscopy (TEM). Furthermore, validation performed with certified NIST Au-NP showed excellent agreement. The developed methods show potential for characterization of other commonly used and important metallic engineered nanoparticles. © 2011 Elsevier B.V

Indium-Free PTB7/PC71BM Polymer Solar Cells with Solution-Processed Al:ZnO Electrodes on PET Substrates

Inverted PTB7/PC71BM polymer solar cells are prepared on solution-processed Al:ZnO transparent contacts on PET substrates. Al:ZnO is deposited by a low temperature chemical bath deposition route (T < 100°C at any step) to comply with the temperature sensitive substrate. A maximum conversion efficiency of 6.4% and 6.9% is achieved for the indium-free solar cells on PET and glass substrates, respectively. The devices are relatively stable in air whereby an initial efficiency loss in the order of 15% after storage for 15 days can be fully recovered by light soaking

Characterization of Silver Nanoparticle Products Using Asymmetric Flow Field Flow Fractionation with a Multidetector Approach – a Comparison to Transmission Electron Microscopy and Batch Dynamic Light Scattering

Due to the already prevalent and increasing use of silver-nanoparticle (Ag-NP) products and the raised concerns in particular for the aquatic environment, analytical techniques for the characterization of such products are of need. However, because Ag-NP products are of different compositions and polydispersities, analysis especially of the size distribution is challenging. In this work, an asymmetric flow field flow fractionation (A4F) multidetector system (UV/vis, light scattering, inductively coupled plasma mass spectrometry - ICPMS), in combination with a method to distinguish and quantify the particle and dissolved Ag fractions (ICPMS after ultracentrifugation), for the characterization of Ag-NP products with different degrees of polydispersities is presented. For validation and to outline benefits and limitations, results obtained from batch dynamic light scattering (batch-DLS) and transmission electron microscopy (TEM) were compared. With the developed method a comprehensive understanding in terms of dissolved Ag and Ag-NP concentration as well as an element selective, mass- and number particle size distribution (PSD) was obtained. In relation to batch-DLS, the reliability of the data was improved significantly. In comparison to TEM, faster measurement times and the ability to determine the samples directly in dispersions are clearly advantageous. The proposed setup shows potential for a rapid- and reliable characterization method of virtually any polydisperse metallic NP dispersion, many of them available on the market already

Critical aspects of sample handling for direct nanoparticle analysis and analytical challenges using asymmetric field flow fractionation in a multi-detector approach

The analysis of engineered nanomaterials (ENMs), especially nanoparticles (ENPs) is a fast growing analytical research field. New trends in plasma spectrometry such as direct single particle inductively coupled plasma mass spectrometry (spICPMS) or the coupling of asymmetric flow field flow fractionation to ICPMS (A4F-ICPMS) allow direct analysis of ENPs by getting not only chemical but also size information simultaneously. However, in both techniques dilution of ENP samples is needed or occurs during analysis. The colloidal stability and the agglomeration behavior depend on the ENP-type, coating agent and also on the surrounding media. The stability of charge stabilized ENPs is especially sensitive to changes of pH or ionic strength, sometimes even to dilution. Although the stability of sterically stabilized ENP is typically less affected by the above mentioned factors, agglomeration can still occur in certain environments. Thus, storage, handling and sample preparation is a big challenge in ENP analysis. Kinetic studies of different ENPs, representative for typical nanoparticle types and coatings, point out that the behavior is dependent on various influencing factors pertaining to the chemical environment (pH, ionic strength, dilution). In this study polyvinyl alcohol (Ag@PVA) and citrate (Ag@citrate) stabilized silver nanoparticles, as well as titanium oxide ENPs coated with poly-acrylate (TiO2@PA) have been studied. A simple analytical approach using batch analysis with dynamic light scattering (DLS) is proposed for a fast assessment of samples containing unknown ENP types or structures. Furthermore, unwanted particle-membrane-interactions, which often lead to inappropriate recovery rates in A4F fractionation, are investigated. They are caused by the electrostatic charges carried by different membrane materials and the resulting interaction with the ENP charge. This is critically discussed for membrane materials typical for A4F analysis: polyethersulfone (PES), regenerated cellulose (RC), and polyvinylidene difluoride (PVDF)