Environmental Conditions Influencing Sorption of Inorganic Anions to Multiwalled Carbon Nanotubes Studied by Column Chromatography

Sorption to carbon-based nanomaterials is typically studied in batch experiments. An alternative method offering advantages to study sorption is column chromatography. Sorbent packed columns are used and sorption data are determined by relating sorbate retention to that of a nonretarded tracer. We have now for the first time applied this technique to study the influence of environmental conditions on sorption of inorganic anions (bromide, nitrite, nitrate, and iodide) to multiwalled carbon nanotubes. Deuterium oxide was used as nonretarded tracer. Sorption isotherms were best described by the Freundlich model. Sorption increased in the order bromide < nitrite < nitrate < iodide. Increasing ionic strength from 1 mM to 100 mM sodium chloride significantly reduced or completely suppressed sorption (bromide, nitrite) due to competition with chloride. pH strongly affected sorption as negatively charged analytes were attracted by the positively charged surface at pH 3. At pH > 4.5 the surface charge was negative, but sorption was still detectable at pH 6 and 9. Consequently, other forces than electrostatic attraction contributed to sorption. These forces may include H-bonding as indicated by sorption enthalpy determined by variation of column temperature. Overall, column chromatography represents a promising alternative in sorption studies to reveal sorbent properties

Sorption of Heterocyclic Organic Compounds to Multiwalled Carbon Nanotubes

Sorption is an important natural and technical process. Sorption coefficients are typically determined in batch experiments, but this may be challenging for weakly sorbing compounds. An alternative method enabling analysis of those compounds is column chromatography. A column packed with the sorbent is used and sorption data are determined by relating sorbate retention to that of a nonretarded tracer. In this study, column chromatography was applied for the first time to study sorption of previously hardly investigated heterocyclic organic compounds to multiwalled carbon nanotubes (MWCNTs). Sorption data for these compounds are very limited in literature, and weak sorption is expected from predictions. Deuterium oxide was used as nonretarded tracer. Sorption isotherms were well described by the Freundlich model and data showed reasonable agreement with predicted values. Sorption was exothermic and physisorption was observed. H-bonding may contribute to overall sorption, which is supported by reduced sorption with increasing ionic strength due to blocking of functional groups. Lowering pH reduced sorption of ionizable compounds, due to electrostatic repulsion at pH 3 where sorbent as well as sorbates were positively charged. Overall, column chromatography was successfully used to study sorption of heterocyclic compounds to MWCNTs and could be applied for other carbon-based sorbents

A New Chemometric Approach for Automatic Identification of Microplastics from Environmental Compartments Based on FT-IR Spectroscopy

One key step studying interactions of microplastics with our ecological system is to identify plastics within environmental samples. Aging processes and surface contamination especially with biofilms impede this characterization. A complex and time-consuming cleaning procedure is a common solution for this problem. However, it implies an artificial change of sample composition with a risk of losing important information or even damaging microplastic particles. In the present work, we introduce a new chemometric approach to identify heavily weathered and contaminated microplastics without any cleaning. The main idea of this concept is based on an automated curve fitting of most relevant vibrational bands to calculate a highly characteristic fingerprint that contains all vibrational band area ratios. This new data set will be used to estimate the similarity of samples and reference standards for identification. A total of 300 individual naturally weathered plastic particles were measured with <i>Fourier</i> transformation infrared spectroscopy in attenuated total reflection mode (FT-IR ATR) and identified successfully with the new method. To that end, all samples were compared with a selection of common reference plastics and bio polymers. As it turns out, the accuracy of identification rises significantly from 76% by means of conventional library searching algorithms to 96% by identifying microplastics with our new method. Therefore, the new approach can be a useful tool to compare and describe similarities of FT-IR spectra of microplastics, which may improve further research studies on this topic

Universal Route to Polycyclic Aromatic Hydrocarbon Analysis in Foodstuff: Two-Dimensional Heart-Cut Liquid Chromatography–Gas Chromatography–Mass Spectrometry

Analysis of polycyclic aromatic hydrocarbons (PAHs) in complex foodstuff is associated with complicated and work-intensive sample preparation. Chromatographic interference has to be faced in many situations. The scope of the current work was the development of a highly efficient two-dimensional heart-cut LC-LC-GC-MS method. Detection was performed with a time-of-flight mass spectrometer (TOF-MS) to allow for a comprehensive evaluation of the obtained data in terms of cleanup efficiency. Additionally, routine detection was performed with single quadrupole MS. An easy and quick generic sample preparation protocol was realized as a first step. During method development, focus was given to optimizing HPLC cleanup for complex foodstuff. Silica-, polymeric-, and carbon-based HPLC phases were tested. Coupling of silica gel to π-electron acceptor modified silica gel showed the best cleanup properties. A four rotary valve configuration allowed the usage of a single binary HPLC pump. Screening of several fatty and nonfatty food matrices showed the absence of unwanted matrix compounds in the cleaned-up PAH fraction down to the low picogram range using TOF-MS. Limits of quantitation (LOQ) were below 0.1 μg/kg for all EU priority PAHs. Recovery rates ranged from 82 to 111%. Validation data fully complied with EU Regulation 836/2011. Sample preparation was possible in 20 min. Interlacing of HPLC and GC allowed an average method runtime of 40 min per sample

How Redox Conditions and Irradiation Affect Sorption of PAHs by Dispersed Fullerenes (nC60)

Surface properties, dispersion state, and sorption behavior of carbon-based nanomaterials will change after being released into the environment. To study these processes, five different scenarios were considered to probe the impact of changes in surface properties of dispersed fullerenes (nC60) on their sorption potential due to irradiation and presence of oxygen. Sorption isotherms of pyrene by nC60 were determined at environmentally relevant concentrations applying a passive sampling method. Isotherms of all dispersion scenarios were best fit with the Dubinin–Ashthakov model. Sorption was strongest for nC60 kept under anoxic condition. Both the presence of oxygen and irradiation significantly decreased the sorption capacity of nC60, while commercially available polyhydroxy fullerenes had the smallest sorption. In addition, competition for sorption sites was never observed in multiple sorbate experiments with four polycyclic aromatic hydrocarbons at small concentration. A strong relationship between sorption coefficients and hydrophobic properties of sorbates suggests that hydrophobic interactions are of major importance. The results emphasize that aging of released fullerenes results in a reduced strength of interactions with nonpolar compounds and, thus, reduces the impact on the environmental transport of hydrophobic pollutants

A New Reaction Pathway for Bromite to Bromate in the Ozonation of Bromide

Ozone is often used in the treatment of drinking water. This may cause problems if the water to be treated contains bromide as its reaction with ozone leads to the formation of bromate, which is considered to be carcinogenic. Bromate formation is a multistep process resulting from the reaction of ozone with bromite. Although this process seemed to be established, it has been shown that ozone reacts with bromite not by the previously assumed mechanism via O transfer but via electron transfer. Besides bromate, the electron-transfer reaction also yields O₃^•–, the precursor of OH radicals. The experiments were set up in such a way that OH radicals are not produced from ozone self-decomposition but solely by the electron-transfer reaction. This study shows that hydroxyl radicals are indeed generated by using tBuOH as the OH radical scavenger and measuring its product, formaldehyde. HOBr and bromate yields were measured in systems with and without tBuOH. As OH radicals contribute to bromate formation, higher bromate and HOBr yields were observed in the absence of tBuOH than in its presence, where all OH radicals are scavenged. On the basis of the results presented here, a pathway from bromide to bromate, revised in the last step, was suggested

Origin of Xylitol in Chewing Gum: A Compound-Specific Isotope Technique for the Differentiation of Corn- and Wood-Based Xylitol by LC-IRMS

The sugar replacement compound xylitol has gained increasing attention because of its use in many commercial food products, dental-hygiene articles, and pharmaceuticals. It can be classified by the origin of the raw material used for its production. The traditional “birch xylitol” is considered a premium product, in contrast to xylitol produced from agriculture byproducts such as corn husks or sugar-cane straw. Bulk stable-isotope analysis (BSIA) and compound-specific stable-isotope analysis (CSIA) by liquid-chromatography isotope-ratio mass spectrometry (LC-IRMS) of chewing-gum extracts were used to determine the δ¹³C isotope signatures for xylitol. These were applied to elucidate the original plant type the xylitol was produced from on the basis of differences in isotope-fractionation processes of photosynthetic CO₂ fixation. For the LC-IRMS analysis, an organic-solvent-free extraction protocol and HPLC method for the separation of xylitol from different artificial sweeteners and sugar-replacement compounds was successfully developed and applied to the analysis of 21 samples of chewing gum, from which 18 could be clearly related to the raw-material plant class

Reaction of Gadolinium Chelates with Ozone and Hydroxyl Radicals

Gadolinium chelates are used in increasing amounts as contrast agents in magnetic resonance imaging, and their fate in wastewater treatment has recently become the focus of research. Oxidative processes, in particular the application of ozone, are currently discussed or even implemented for advanced wastewater treatment. However, reactions of the gadolinium chelates with ozone are not yet characterized. In this study, therefore, rate constants with ozone were determined for the three commonly used chelates Gd-DTPA, Gd-DTPA-BMA, and Gd-BT-DO3A, which were found to be 4.8 ± 0.88, 46 ± 2.5, and 24 ± 1.5 M^–1 s^–1, respectively. These low rate constants indicate that a direct reaction with ozone in wastewater is negligible. However, application of ozone in wastewater leads to substantial yields of ^•OH. Different methods have been applied and compared for determination of <i>k</i>_{(^•OH+Gd chelate)}. From rate constants determined by pulse radiolysis experiments (<i>k</i>_{(^•OH+Gd‑DTPA)} = 2.6 ± 0.2 × 10⁹ M^–1 s^–1, <i>k</i>_{(^•OH+Gd‑DTPA‑BMA)} = 1.9 ± 0.7 × 10⁹ M^–1 s^–1, <i>k</i>_{(^•OH+Gd‑BT‑DO3A)} = 4.3 ± 0.2 × 10⁹ M^–1 s^–1), it is concluded that a reaction in wastewater via ^•OH radicals is feasible. Toxicity has been tested for educt and product mixtures of both reactions. Cytotoxicity (MTT test) and genotoxicity (micronuclei assay) were not detectable

Online and Splitless NanoLC × CapillaryLC with Quadrupole/Time-of-Flight Mass Spectrometric Detection for Comprehensive Screening Analysis of Complex Samples

A novel multidimensional separation system based on online comprehensive two-dimensional liquid chromatography and hybrid high-resolution mass spectrometry has been developed for the qualitative screening analysis and characterization of complex samples. The core of the system is a consistently miniaturized two-dimensional liquid chromatography that makes the rapid second dimension compatible with mass spectrometry without the need for any flow split. Elevated temperature, ultrahigh pressure, and a superficially porous sub-3-μm stationary phase provide a fast second dimension separation and a sufficient sampling frequency without a first dimension flow stop. A highly loadable porous graphitic carbon stationary phase is employed in the first dimension to implement large volume injections that help countervailing dilution caused by the sampling process between the two dimensions. Exemplarily, separations of a 99-component standard mixture and a complex wastewater sample were used to demonstrate the performance of the dual-gradient system. In the second dimension, 30 s gradients at a cycle time of 1 min were employed. One multidimensional separation took 80–90 min (∼120 min including extended hold and re-equilibration in the first dimension). This approach represents a cost-efficient alternative to online LC × LC strategies working with conventionally sized columns in the rapid second dimension, as solvent consumption is drastically decreased and analytes still are detectable at environmentally relevant concentrations

Degradation of Polymeric Brominated Flame Retardants: Development of an Analytical Approach Using PolyFR and UV Irradiation

Many well-established methods for studying the degradation of brominated flame retardants are not useful when working with polymeric and water insoluble species. An example for this specific class of flame retardants is PolyFR (polymeric flame retardant; CAS No 1195978–93–8), which is used as a substituent for hexabromocyclododecane. Although it has been on the market for two years now, almost no information is available about its long time behavior in the environment. Within this study, we focus on how to determine a possible degradation of both pure PolyFR as well as PolyFR in the final insulation product, expanded polystyrene foam. Therefore, we chose UV radiation followed by analyses of the total bromine content at different time points via ICP-MS and identified possible degradation products such as 2,4,6-tribromophenol through LC-MS. These results were then linked with measurements of the adsorbable organically bound bromine and total organic carbon in order to estimate their concentrations. With respect to the obtained ¹H NMR, GPC, and contact angle results, the possibility for further degradation was discussed, as UV irradiation can influence the decomposition of molecules in combination with other environmental factors like biodegradation