Dicationic ionic liquid stationary phase for GC-MS analysis of volatile compounds in herbal plants

The seeming “dual nature” of ionic liquids (ILs) for separating both apolar and polar compounds suggests that ILs may have a great potential for complex samples like essential oils from herbal plants that contain a great variety of compounds. In the present work, a geminal dicationic IL, 1,9-di(3-vinylimidazolium)nonane bis[(trifluoromethyl)sulfonyl]imidate, was investigated for this purpose. To find the best way to achieve satisfactory separations simultaneously for the compounds in essential oils, the dicationic IL was used as the stationary phase for capillary gas chromatography (GC) in two ways, either in its pure state or as a mixed stationary phase with monocationic ILs and a polysiloxane diluent. Interestingly, it was found that the mixed stationary phase exhibited a much better selectivity for polar and nonpolar compounds than either the dicationic IL or the polysiloxane, suggesting that a kind of synergistic effect occurred when these stationary phases were combined in the way described. A comparison with two commercial stationary phases (polar and nonpolar) indicated that this novel mixed stationary phase behaved in a way closer to a polar stationary phase in terms of selectivity and elution order. The present work demonstrates that the mixed stationary phase is efficient and selective and can be an alternative choice for the GC analysis of samples of complex composition. Figure Divinyldiimidazolium-based ionic liquid stationary phase     

Optimization of a sensitive method for the determination of nitro musk fragrances in waters by solid-phase microextraction and gas chromatography with micro electron capture detection using factorial experimental design

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen–polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane–divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100 °C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified. Figure Stardardized Pareto charts for the main effects and interactions     

SPME in environmental analysis

Recent advances in the use of solid-phase microextraction (SPME) in environmental analysis, including fiber coatings, derivatization techniques, and in-tube SPME, are reviewed in this article. Several calibration methods for SPME, including traditional calibration methods, the equilibrium extraction method, the exhaustive extraction method, and several diffusion-based calibration methods, are presented. Recent developed SPME devices for on-site sampling and several applications of SPME in environmental analysis are also introduced.      

Classification of bacteria by simultaneous methylation–solid phase microextraction and gas chromatography/mass spectrometry analysis of fatty acid methyl esters

Direct methylation and solid-phase microextraction (SPME) were used as a sample preparation technique for classification of bacteria based on fatty acid methyl ester (FAME) profiles. Methanolic tetramethylammonium hydroxide was applied as a dual-function reagent to saponify and derivatize whole-cell bacterial fatty acids into FAMEs in one step, and SPME was used to extract the bacterial FAMEs from the headspace. Compared with traditional alkaline saponification and sample preparation using liquid–liquid extraction, the method presented in this work avoids using comparatively large amounts of inorganic and organic solvents and greatly decreases the sample preparation time as well. Characteristic gas chromatography/mass spectrometry (GC/MS) of FAME profiles was achieved for six bacterial species. The difference between Gram-positive and Gram-negative bacteria was clearly visualized with the application of principal component analysis of the GC/MS data of bacterial FAMEs. A cross-validation study using ten bootstrap Latin partitions and the fuzzy rule building expert system demonstrated 87 ± 3% correct classification efficiency.      

Recent developments in solid-phase microextraction

The main objective of this review is to describe the recent developments in solid-phase microextraction technology in food, environmental and bioanalytical chemistry applications. We briefly introduce the historical perspective on the very early work associated with the development of theoretical principles of SPME, but particular emphasis is placed on the more recent developments in the area of automation, high-throughput analysis, SPME method optimization approaches and construction of new SPME devices and their applications. The area of SPME automation for both GC and LC applications is particularly addressed in this review, as the most recent developments in this field have allowed the use of this technology for high-throughput applications. The development of new autosamplers with SPME compatibility and new-generation metal fibre assemblies has enhanced sample throughput for SPME-GC applications, the latter being attributed to the possibility of using the same fibre for several hundred extraction/injection cycles. For LC applications, high-throughput analysis (>1,000 samples per day) can be achieved for the first time with a multi-SPME autosampler which uses multi-well plate technology and allows SPME sample preparation of up to 96 samples in parallel. The development and evolution of new SPME devices such as needle trap, thin-film microextraction and cold-fibre headspace SPME have offered significant improvements in performance characteristics compared with the conventional fibre-SPME arrangement. Figure Photo of a high-throughput multi-fibre SPME PAS autosampler     

Headspace mass spectrometry methodology: application to oil spill identification in soils

In the present work we report the results obtained with a methodology based on direct coupling of a headspace generator to a mass spectrometer for the identification of different types of petroleum crudes in polluted soils. With no prior treatment, the samples are subjected to the headspace generation process and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of volatiles in the sample analysed. The mass spectrum corresponding to the mass/charge ratios (m/z) contains the information related to the composition of the headspace and is used as the analytical signal for the characterization of the samples. The signals obtained for the different samples were treated by chemometric techniques to obtain the desired information. The main advantage of the proposed methodology is that no prior chromatographic separation and no sample manipulation are required. The method is rapid, simple and, in view of the results, highly promising for the implementation of a new approach for oil spill identification in soils. Figure PCA score plots illustrate clear discrimination of types of crude oil in polluted soil samples (e.g. results are shown for vertisol)     

Using the solvation parameter model to characterize functionalized ionic liquids containing the tris(pentafluoroethyl)trifluorophosphate (FAP) anion

Ionic liquids (ILs) containing the tris(pentafluoroethyl)trifluorophosphate anion [FAP]⁻ have attracted increased attention due to their unique properties including ultrahigh hydrophobicity, hydrolytic stability, and wide electrochemical window. In this study, the solvation parameter model is used via gas chromatography to characterize the solvation interactions of seven ILs containing amino, ester, and hydroxyl functional groups appended to the cation and paired with [FAP]⁻, as well as three ILs containing the bis[(trifluoromethyl)sulfonyl]imide anion [NTf₂]⁻. The role of the functional groups, nature of the counter anion, and cation type on the system constants were evaluated. ILs containing [FAP]⁻ possessed lower hydrogen bond basicity than NTf₂-based ILs having the same cationic component; in the case of hydroxyl-functionalized cations, the presence of [FAP]⁻ led to an enhancement of the hydrogen bond acidity, relative to the NTf₂-analogs. The system constants support the argument that [FAP]⁻ weakly coordinates the cation and any appended functional groups, promoting properties of the cation which might be masked by stronger interactions with other anion systems. The chromatographic performance of the IL stationary phases was evaluated by examining the retention behavior and separation selectivity for chosen analytes. The results from this work can be used as a guide for choosing FAP-based ILs capable of exhibiting desired solvation properties while retaining important physical properties including high thermal stability and high hydrophobicity. Figure In this study, the solvation parameter model is used via gas chromatography to characterize the solvation interactions of seven ILs containing amino, ester, and hydroxyl functional groups appended to the cation and paired with tris(pentafluoroethyl)trifluorophosphate [FAP]⁻, as well as three ILs containing the bis[(trifluoromethyl)sulfonyl]imide anion [NTf₂]⁻. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Enzyme-functionalized mesoporous silica for bioanalytical applications

The unique properties of mesoporous silica materials (MPs) have attracted substantial interest for use as enzyme-immobilization matrices. These features include high surface area, chemical, thermal, and mechanical stability, highly uniform pore distribution and tunable pore size, high adsorption capacity, and an ordered porous network for free diffusion of substrates and reaction products. Research demonstrated that enzymes encapsulated or entrapped in MPs retain their biocatalytic activity and are more stable than enzymes in solution. This review discusses recent advances in the study and use of mesoporous silica for enzyme immobilization and application in biosensor technology. Different types of MPs, their morphological and structural characteristics, and strategies used for their functionalization with enzymes are discussed. Finally, prospective and potential benefits of these materials for bioanalytical applications and biosensor technology are also presented. Figure Enzyme-functionalized mesoporous silica fibers and their integration in a biosensor design. The immobilization process takes place essentially in the silica micropores.     

Anion exchange silica monolith for capillary liquid chromatography

An anion exchange monolithic silica capillary column was prepared by surface modification of a hybrid monolithic silica capillary column prepared from a mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS). The surface modification was carried out by on-column copolymerization of N-[3-(dimethylamino)propyl]acrylamide methyl chloride-quaternary salt (DMAPAA-Q) with 3-methacryloxypropyl moieties bonded as an anchor to the silica surface to form a strong anion exchange stationary phase. The columns were examined for their performance in liquid chromatography (LC) and capillary electrochromatography (CEC) separations of common anions. The ions were separated using 50 mM phosphate buffer at pH 6.6. Evaluation by LC produced an average of 30,000 theoretical plates (33 cm column length) for the inorganic anions and nucleotides. Evaluation by CEC, using the same buffer, produced enhanced chromatographic performance of up to ca. 90,000 theoretical plates and a theoretical plate height of ca. 4 μm. Although reduced efficiency was observed for inorganic anions that were retained a long time, the results of this study highlight the potential utility of the DMAPAA-Q stationary phase for anion separations. Figure Micro-LC performance evaluation of a strong anion exchange silica monolith column, 100H-MOP-DMAPAA-Q, 33 cm in length, with a mobile phase of 50 mM phosphate buffer, pH 2.8; linear velocity: u = 1.8 mm/s; UV-Vis detection at 254 nm. Sample solution (5 mg/mL of each component, 4 mL) was injected in split flow injection mode at a split ratio of ca. 1:1900 with a pump flow rate of 1.5 mL/min     

Characterization of volatile organic compounds and odors by in-vivo sampling of beef cattle rumen gas, by solid-phase microextraction, and gas chromatography–mass spectrometry–olfactometry

Volatile organic compounds (VOCs) and odors in cattle rumen gas have been characterized by in-vivo headspace sampling by solid-phase microextraction (SPME) and analysis by gas chromatography–mass spectrometry–olfactometry (GC–MS–O). A novel device enabling headspace SPME (HS-SPME) sampling through a cannula was designed, refined, and used to collect rumen gas samples from steers. A Carboxen–polydimethylsiloxane (PDMS) fiber (85 μm) was used for SPME sampling. Fifty VOCs from ten chemical groups were identified in the rumen headspace. The VOCs identified had a wide range of molecular weight (MW) (34 to 184), boiling point (−63.3 to 292 °C), vapor pressure (1.05 × 10⁻⁵ to 1.17 × 10² Pa), and water solubility (0.66 to 1 × 10⁶ mg L⁻¹). Twenty-two of the compounds have a published odor detection thresholds (ODT) of less than 1 ppm. More than half of the compounds identified are reactive and have an estimated atmospheric lifetime of <24 h. The amounts of VFAs, sulfide compounds, phenolic compounds, and skatole, and the odor intensity of VFAs and sulfide compounds in the rumen gas were all higher after feeding than before feeding. These results indicate that rumen gases can be an important potential source of aerial emissions of reactive VOCs and odor. In-vivo sampling by SPME then GC–MS–O analysis can be a useful tool for qualitative characterization of rumen gases, digestion, and its relationship to odor and VOC formation. Figure Modified cannula for rumen gas sampling with SPME     

Evaluation of solid-phase microextraction conditions for the determination of polycyclic aromatic hydrocarbons in aquatic species using gas chromatography

This paper describes a headspace solid-phase microextraction (HS-SPME) procedure coupled to gas chromatography with mass spectrometric detection (GC–MS) for the determination of eight PAHs in aquatic species. The influence of various parameters on the PAH extraction efficiency was carefully examined. At 75 °C and for an extraction time of 60 min, a polydimethylsiloxane–divinylbenzene (PDMS/DVB) fiber coating was found to be most suitable. Under the optimized conditions, detection limits ranged from 8 to 450 pg g⁻¹, depending on the compound and the sample matrix. The repeatability varied between 7 and 15% (RSD). Accuracy was tested using the NIST SRM 1974b reference material. The method was successfully applied to different samples, and the studied PAHs were detected in several of the samples. Figure Headspace SPME sampling followed by GC–MS facilitates routine monitoring of PAHs in aquatic species     

Combining silica-based adsorbents and SPME fibers in the extraction of the volatiles of beer: an exploratory study

A series of silica-based materials were employed as sorbents within solid-phase microextraction vials. The aim of the study was to evaluate the effect of an additional phase on the distribution of the volatile and less volatile analytes. The adsorption of six probe molecules, namely isoamyl acetate, ethyl hexanoate (ethyl caproate), phenylethyl alcohol, ethyl octanoate (ethyl caprilate), 2-phenylethyl acetate, and ethyl decanoate, was monitored by detecting the desorbed amount on a DVD–CAR–PDMS fiber from Pilsen beer. The microextraction process involved the presence of different silica-based phases produced via different methods: xerogel produced by hydrolytic and non-hydrolytic routes, aerogel, pyrogenic, and precipitated silica. The resulting data are discussed in correlation with sorbent texture properties (specific area and pore diameter). The modification of silica with alkyl groups also affects the preconcentrated amount of the target molecules in the headspace. The presence of sorbents was shown to affect the analyte signal more than the addition of NaCl or the use of ultrasound. Analyte’s equilibrium between fiber and sorbent     

Headspace solid-phase microextraction gas chromatography tandem mass spectrometry for the determination of brominated flame retardants in environmental solid samples

A headspace solid-phase microextraction gas chromatography coupled with tandem mass spectrometry (HSSPME-GC-MS-MS) methodology for determination of brominated flame retardants in sediment and soil samples is presented. To the best of our knowledge, this is the first time that SPME has been applied to analyze polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in environmental solid samples. Analyses were performed using 0.5-g solid samples moisturized with 2 mL water, employing a polydimethylsiloxane (PDMS) fiber coating, exposed to the headspace at 100 °C for 60 min. Several types of environmental solid samples were included in this study and the extraction efficiency was related to the organic matter content of the sample. Calibration was performed using real samples, and the method showed good linearity over a wide concentration range, precision, and afforded quantitative recoveries. The obtained detection limits were in the sub-ng g⁻¹ for all the target analytes in both samples. The proposed procedure was applied to several marine and river sediments and soils, some of which were found to contain PBDEs at concentrations in the ng g⁻¹ level; BDE-47, BDE-100, and BDE-99 were the major congeners detected. The proposed method constitutes a rapid and low-cost alternative for the analysis of the target brominated flame retardants in environmental solid samples, since the clean-up steps, fractionation, and preconcentration of extracts inherent to the classical multi-step solvent extraction procedures are avoided.      

Modelling of toluene solid-phase microextraction for indoor air sampling

Solid-phase microextraction (SPME) is a convenient and efficient sampling technique recently applied to indoor air analysis. We propose here a theoretical model of the adsorption kinetics of toluene on SPME fibre under static extraction conditions. We discuss the effects of sampling volume and initial concentration of analyte on the adsorption kinetics. This model is used to estimate the limits of detection taking into account operating conditions and to calculate theoretical calibration curves. Results of comparison with experimental data are encouraging: only 11% difference for calibration curves and 30% for the estimation of the limit of detection. On the basis of this kinetics model, the solid concentration gradient in the Carboxen coating was modelled with Fick’s second law of diffusion in unsteady-state mass-transfer mode. Mass diffusion from the gas sample to the SPME fibre was also investigated. It was shown that diffusion is the limiting step of the mass-transfer process in the static mode. Thus, the model developed, allows a better understanding of adsorption on Carboxen fibre and in the future could be a useful tool for cheap and time-saving development of SPME methods and the estimation of sampling performance. Figure PDMS/Carboxen SPME fibre (scanning electron microscopy – magnification x 220)     

Solid-phase microextraction gas chromatography-mass spectrometry determination of fragrance allergens in baby bathwater

A method based on solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) has been optimized for the determination of fragrance allergens in water samples. This is the first study devoted to this family of cosmetic ingredients performed by SPME. The influence of parameters such as fibre coating, extraction and desorption temperatures, salting-out effect and sampling mode on the extraction efficiency has been studied by means of a mixed-level factorial design, which allowed the study of the main effects as well as two-factor interactions. Excluding desorption temperature, the other parameters were, in general, very important for the achievement of high response. The final procedure was based on headspace sampling at 100 °C, using polydimethylsiloxane/divinylbenzene fibres. The method showed good linearity and precision for all compounds, with detection limits ranging from 0.001 to 0.3 ng mL⁻¹. Reliability was demonstrated through the evaluation of the recoveries in different real water samples, including baby bathwater and swimming pool water. The absence of matrix effects allowed the use of external standard calibration to quantify the target compounds in the samples. The proposed procedure was applied to the determination of allergens in several real samples. All the target compounds were found in the samples, and, in some cases, at quite high concentrations. The presence and the levels of these chemicals in baby bathwater should be a matter of concern. Baby exposure to fragrance allergens and other cosmetic ingredients through the daily bath     

Size characterization of drug-loaded polymeric core/shell nanoparticles using asymmetrical flow field-flow fractionation

Asymmetrical flow field-flow fractionation (AsFlFFF) was used to determine the size distribution of drug-loaded core/shell nanoparticles which have a lipid core of lecithin and a polymeric shell of a Pluronic. AsFlFFF provided separation of the drug-loaded core/shell nanoparticles from smaller coreless polymeric micelles, thus allowing accurate size analysis of the drug-loaded nanoparticles without interference by the coreless micelles. It was found from AsFlFFF that the drug-loaded nanoparticles have broad size distributions ranging from 100 to 600 nm in diameter. It was also found that, after the nanoparticles had been stored for 70 days, they disappeared as a result of self-degradation. Being a separation technique, AsFlFFF seems to be more useful than transmission electron microscopy or dynamic light scattering for size analysis of core/shell nanoparticles, which have broad and bimodal size distributions. Figure Separation by AsFlFFF     

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Further research on the photo-SPME of triclosan

In this study the photoinduced degradation of triclosan has been investigated by photo-solid-phase microextraction (photo-SPME). In photo-SPME, photodegradation is carried out on the SPME fibre containing the target compound. Triclosan was extracted from aqueous solutions by use of polydimethylsiloxane SPME fibres and these were subsequently exposed to UV irradiation (power 8 W, wavelength 254 nm) for different times (from 2 to 60 min). The photodegradation kinetics of triclosan were investigated, the photoproducts generated were tentatively identified, and the photochemical behaviour of these products was studied by use of this on-fibre approach followed by gas chromatographic–mass spectrometric analysis. Eight photoproducts were tentatively identified, including chlorinated phenols, chlorohydroxydiphenyl ethers, 2,8-dichlorodibenzo-p-dioxin, and a possible dichlorodibenzodioxin isomer or dichlorohydroxydibenzofuran. The main photodegradation mechanisms were postulated and photodegradation pathways proposed. The effect of pH on triclosan degradation and on triclosan-to-dioxin conversion was also investigated. Triclosan degradation occurred, and generation of 2,8-dichlorodibenzo-p-dioxin was confirmed, throughout the pH range studied (from 3 to 9).      

Real-life application of a QCM-based e-nose: quantitative characterization of different plant-degradation processes

Continuous surveillance of composting processes would enable a feedback loop to be obtained for both analysis and process control. For this purpose, we designed e-noses based on a six-electrode quartz-crystal microbalance (QCM) array coated with affinity materials and molecularly imprinted polymers (MIP). They enable quantitative monitoring of volatile organic compounds (VOCs) emitted directly in a compost bin and are highly suitable tools for achieving on-line characterization of the degradation processes occurring. During grass and pine composting (duration 14 days and 40 days, respectively), we observed concentrations of up to 250 ppm of esters, 700 ppm of alcohols, 250 ppm of terpenes, and 90% relative humidity directly on-line with such a system and could validate the data off-line by GC-MS. The sensor also gave direct insight into the differences between the two composting batch types. Besides duration, during grass composting larger amounts of alcohols are emitted whereas relative amount of terpenes is twice as high for pine composting. Detailed correlation of the sensor and the GC-MS data allows approximate estimation of the sensitivity of the sensor materials towards analyte classes such as, e.g., aliphatic alcohols or terpenes. Figure Mass sensitive sensor arrays coated with different molecularly imprinted and affinity materials are a highly suitable tool for quantitatively monitoring solvent patterns during composting procedures on-line in a composter headspace. Dedicated to Professor Udo Brinker on the occasion of his 65th birthday.     

Adsorption of mercury ions by mercapto-functionalized amorphous silica

Amorphous silicas have been functionalized by two different methods. In the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the silica surface to give the chlorinated silica Cl-Sil. In a second reaction, multifunctionalized N,S donor compounds were incorporated to obtain the functionalized silicas, which are denoted as L-Sil-Het (where L=mercaptothiazoline, mercaptopyridine or mercaptobenzothiazole). In the homogeneous route, the functionalization was achieved through a one-step reaction between the silica and an organic ligand containing the chelating functions; this gave the modified silicas denoted as L-Sil-Hom. The functionalized silicas were characterized by elemental analysis, IR spectroscopy and thermogravimetry. These materials were employed as adsorbents for mercury cations from aqueous and acetone solutions at room temperature. The results indicate that, in all cases, mercury adsorption was higher in the modified silicas prepared by the homogeneous method. Figure