Improved separation of complex polycyclic aromatic hydrocarbon mixtures using novel column combinations in GC × GC/ToF-MS

Complex mixtures of polycyclic aromatic hydrocarbons (PAHs) are difficult to resolve because of the high degree of overlap in compound vapor pressures, boiling points, and mass spectral fragmentation patterns. The objective of this research was to improve the separation of complex PAH mixtures (including 97 different parent, alkyl-, nitro-, oxy-, thio-, chloro-, bromo-, and high molecular weight PAHs) using GC × GC/ToF-MS by maximizing the orthogonality of different GC column combinations and improving the separation of PAHs from the sample matrix interferences, including unresolved complex mixtures (UCM). Four different combinations of nonpolar, polar, liquid crystal, and nanostationary phase columns were tested. Each column combination was optimized and evaluated for orthogonality using a method based on conditional entropy that considers the quantitative peak distribution in the entire 2D space. Finally, an atmospheric particulate matter with diameter <2.5 μm (PM(2.5)) sample from Beijing, China, a soil sample from St. Maries Creosote Superfund Site, and a sediment sample from the Portland Harbor Superfund Site were analyzed for complex mixtures of PAHs. The highest chromatographic resolution, lowest synentropy, highest orthogonality, and lowest interference from UCM were achieved using a 10 m × 0.15 mm × 0.10 μm LC-50 liquid crystal column in the first dimension and a 1.2 m × 0.10 mm × 0.10 μm NSP-35 nanostationary phase column in the second dimension. In addition, the use of this column combination in GC × GC/ToF-MS resulted in significantly shorter analysis times (176 min) for complex PAH mixtures compared to 1D GC/MS (257 min), as well as potentially reduced sample preparation time.     

Sorption of polycyclic aromatic hydrocarbons to oil contaminated sediment: unresolved complex?

Oil is ubiquitous in aquatic sediments and may affect partitioning and bioavailability of hydrophobic organic chemicals (HOCs). In contrast to other sedimentary hydrophobic carbon phases (natural organic matter, soot-like materials), oil residues have hardly received any attention as far as it concerns effects on HOC sorption. This paper describes experimental work dealing with such effects of oil on polycyclic aromatic hydrocarbon (PAH) sorption to sediments. Three different oils were spiked to a marine sediment in concentrations between 0 and 100 g/kg. Sediment-water distribution coefficients (Kd) for six deuterated PAHs were then determined either directly after spiking the oil or after a semi-natural weathering process in the lab (lasting for more than 2 yr). Resulting Kd values demonstrated sorption-reducing (competitive) effects at relatively low oil concentrations and sorption-enhancing effects at high oil concentrations. The latter effects only occurred above a certain threshold [i.e., ca. 15% (w/w) of oil on a sedimentary organic carbon basis] marking the oil concentration at which the hydrocarbon mixture presumably starts forming separate phases. Assuming a two-domain (organic carbon + oil) distribution model, oil-water distribution coefficients (K(oil)) for PAHs were estimated. For fresh oils, log K(oil) values appeared to be very similar for different types of oils, proportional to log K(OW) values and indistinguishable from log K(OC) values. For weathered oils, K(oil) values were also rather independent of the type of oil, but the affinity of low molecular weight PAHs for weathered oil residues appeared to be extremely high, even higher than values reported for most types of soot. Because affinities of high molecular weight PAHs for oils had not changed upon weathering, sorption of all PAHs studied (comprising a log K(OW) range of 4.6-6.9) to the weathered oil residues appeared to be more or less constant (averaged log K(oil) = 7.0 +/- 0.24). These results demonstrate that it is crucial to take the presence of oil and its weathering state into account when assessing the actual fate of PAHs in aquatic environments.     

Comparison of donor–acceptor and alumina columns for the clean-up of polycyclic aromatic hydrocarbons from edible oils

Two methods for clean-up and sample enrichment for the analysis of polycyclic aromatic hydrocarbons (PAHs) in edible oils are compared; a clean-up based on a donor–acceptor complex chromatography (DACC) column and a standardized method widely used in the food industry consisting in a low pressure column chromatography with alumina as stationary phase. Both methods are followed by a reversed-phase high-performance liquid chromatography with fluorescence detection for the separation and quantitation of each PAH. Certified materials were used in order to validate the methods. The limits of detection were lower than 1 ng/g and good selectivity was achieved in both cases. The DACC column clean-up is faster and better accuracies were obtained. The advantages and disadvantages of both methods are discussed.     

Lowering of concentration of polycyclic aromatic hydrocarbons in liquid media by sorption into polyethylene terephtalate—a model study

Rapeseed oil and water were spiked with polycyclic aromatic hydrocarbon (PAH) solutions at the total levels of 955.1 and 711.4 g kg^–1, respectively, filled into polyethylene terephtalate (PET) cylindrical receptacles and the PAH concentrations in both liquid media followed for more than 90 h by HPLC. During this time, the PAH concentrations decreased by 315.1 in oil and 212.7 g kg^–1 in water due to an interaction of PAHs with PET. Using a modified kinetic equation, the diffusion coefficients for PAHs in both liquid media were determined. Values of the diffusion coefficients obtained indicate that the polarity of medium did not affect the rate of PAH removal. Calculation of the area occupied by a PAH molecule on the PET surface suggests that either the multilayer adsorption or the diffusion of PAHs into PET bulk came into account as the decisive factor bringing about the decrease of PAH concentrations in both media.     

Determination of polycyclic aromatic hydrocarbons in edible oils and barbecued food by HPLC/UV–Vis detection

Determination of nine polycyclic aromatic hydrocarbons in corn, sunflower, olive oils and barbecued meat and fish by HPLC/UV–Vis method is described. The extraction procedure included a saponification, liquid–liquid extraction and finally purification of PAHs through a house-made silica–alumina column. Chromatographic determination was based on separation of PAHs on ODS column and measurement at 254 nm. All polycyclic aromatic hydrocarbons were separated and analyzed in 12 min on reversed phase ODS column with acetonitrile/water mobile phase at 1.5 mL min⁻¹ flow rate. The detection limits of nine polycyclic aromatic hydrocarbons ranged from 0.26 to 1.15 μg L⁻¹ at a signal/noise ratio of 3. The linearity of the method was between 0.9951 and 0.9996. Oil samples contain different PAHs ranging from 0.44 to 98.92 μg L⁻¹. Barbecuing process increased the concentration (in the range of 2- to 8-fold) and caused the formation of PAHs in food samples.     

Propene poisoning on three typical Fe-zeolites for SCR of NOχ with NH₃: from mechanism study to coating modified architecture

Application of Fe-zeolites for urea-SCR of NO(x) in diesel engine is limited by catalyst deactivation with hydrocarbons (HCs). In this work, a series of Fe-zeolite catalysts (Fe-MOR, Fe-ZSM-5, and Fe-BEA) was prepared by ion exchange method, and their catalytic activity with or without propene for selective catalytic reduction of NO(x) with ammonia (NH(3)-SCR) was investigated. Results showed that these Fe-zeolites were relatively active without propene in the test temperature range (150-550 °C); however, all of the catalytic activity was suppressed in the presence of propene. Fe-MOR kept relatively higher activity with almost 80% NO(x) conversion even after propene coking at 350 °C, and 38% for Fe-BEA and 24% for Fe-ZSM-5 at 350 °C, respectively. It was found that the pore structures of Fe-zeolite catalysts were one of the main factors for coke formation. As compared to ZSM-5 and HBEA, MOR zeolite has a one-dimensional structure for propene diffusion, relatively lower acidity, and is not susceptible to deactivation. Nitrogenated organic compounds (e.g., isocyanate) were observed on the Fe-zeolite catalyst surface. The site blockage was mainly on Fe(3+) sites, on which NO was activated and oxidized. Furthermore, a novel fully formulated Fe-BEA monolith catalyst coating modified with MOR was designed and tested, the deactivation due to propene poisoning was clearly reduced, and the NO(x) conversion reached 90% after 700 ppm C(3)H(6) exposure at 500 °C.     

Effect of supplementation with vitamin D₃ on glucose production pathways in human subjects

Scope: Research reports suggest that vitamin D affects glucose and insulin metabolism; however, the exact mechanisms are unclear. ²H NMR analysis of monoacetone glucose (MAG) after tracer administration provides a non‐invasive method of profiling hepatic glucose metabolism. This study examined the effects of supplementation with vitamin D₃ on contribution of glycogenolysis to glucose production. Methods and results: Tracer administration and biofluid collections were performed with eight healthy females before and following a 4‐wk vitamin D₃ administration period. Following an overnight fast subjects ingested deuterated water and acetaminophen. Full void urine samples were collected after 4 h. ²H NMR spectra of urinary monoacetone glucose were acquired to determine the contribution of glycogenolysis to glucose production. The mean contribution of glycogenolysis to glucose production was 60±13%. Supplementation with vitamin D₃ had no effect on hepatic glucose production. Regression analysis revealed a significant relationship between carbohydrate intake and the contribution of glycogenolysis (β=0.914, p=0.004). Conclusion: In conclusion, we saw no changes in the percentage contribution of glycogenolysis following supplementation with vitamin D₃. The reproducibility of our results and the non‐invasive nature of the method highlight the potential for this method in assessing mechanistic modes of action in future nutritional interventions.     

Carbon isotope signature of polycyclic aromatic hydrocarbons (PAHs): evidence for different sources in tropical and temperate environments?

In tropical soils, naphthalene and, partly also, perylene occur at elevated concentrations while pyrolytic higher molecular weight PAHs are almost absent. We hypothesize that there are recent biological PAH sources in the tropical environment related with woody plants and termites. We used the C isotope signature of individual PAHs in temperate and tropical soils and in tropical wood and termite nests to distinguish different PAH sources. The mean delta13C values of the benzo[b+j+k]fluoranthenes and of benzo[a+e]pyrenes in temperate soils ranged between -24.6/1000 and -25.3/1000, being similar to values reported in the literature for PAHs with pyrolitic origin. The mean delta13C values of perylene decreased in the order temperate soils (-27.0/1000) > termite nests (-31.4/1000) > tropical soil (-32.4/1000), while those of naphthalene (-24.6/1000 to -26.2/1000) were similar among the tropical and temperate soils, tropical wood, and termite nests. Our results support the assumption that perylene in the tropical environment is recently biologically produced, as indicated by the depletion in 13C. The C isotope composition of naphthalene, however, cannot be used to distinguish different sources.     

Occurrence of 15 + 1 EU priority polycyclic aromatic hydrocarbons (PAH) in various types of tea (Camellia sinensis) and herbal infusions

For the analysis of 15 + 1 EU priority PAH in tea and herbal infusions, an online-SPE-LVI-GC-MS method was developed. This method includes sample extraction of the tea and herbal infusions with saponification followed by an automated SPE clean-up step. For brews a liquid–liquid extraction with cyclohexane was performed before an automated SPE clean-up. Gas chromatographic separation was done using an Agilent J&W Select PAH (15 m × 0.15 mm × 0.10 µm) column, which allows the separation of the three benzofluoranthenes as well as triphenylene from chrysene. Method performance criteria such as method linearity, limit of quantitation (LOQ) and repeatability were determined and demonstrated that the method was fit for purpose. The method was used to analyse 15 + 1 EU priority PAH in 91 tea and herbal infusion samples. The levels of PAHs ranged from below 0.5 (LOQ) to 460 µg kg^?1, with a median of 4.7 µg kg^?1 and a mean of 39 µg kg^?1 for BaP, and from below 1.0 (LOQ) to 2700 µg kg^?1, with a median of 39 µg kg^?1 and a mean of 250 µg kg^?1 for total PAH, which were in good agreement with other studies reported in the literature. For the brews prepared under normal house preparation (20 g material in 2 L boiling tap water for 10 min), no total 15 + 1 PAH could be detected above the LOQ. With an extended brewing time of 30 min, a transfer rate between 0.25% and 0.52% could be determined, which results in no exceeding of the maximum limits given by the European Union directive for drinking water (EU Council Directive 98/83/EC).     

Phase solubility studies of terpineol with β-cyclodextrins and stability of the freeze-dried inclusion complex

In present work, phase solubility analysis were conducted for studying the solubility of terpineol, a natural flavor compound with antifungal and disinfectant action, in 2-hydroxypropyl-β-cyclodextrin (HBCD) and in β-cyclodextrin (BCD) aqueous solutions and for calculating the thermodynamic parameters involved in the complex formation. Physical properties of the freeze-dried complexes were also evaluated as a function of water content and storage time. The solubility of terpineol increased linearly as the concentration of BCD or HBCD was increased, confirming the 1:1 stoichiometry of the complex. The negative value of the enthalpy and of the Gibbs energy demonstrated that the process is exothermic and spontaneous. Since complexation gives more ordered systems, the negative value obtained for the entropy change confirms the encapsulation of terpineol both in HBCD and BCD. The water adsorption data and glass transition values obtained revealed that complexation involves the displacement of water molecules from the cavity of the CDs by the guest compound that is being included.     

Effect of NO₂ concentration on dimethylnitronaphthalene yields and isomer distribution patterns from the gas-phase OH radical-initiated reactions of selected dimethylnaphthalenes

Dimethylnitronaphthalene (DMNN) formation yields from the reactions of 1,7- and 2,7- dimethylnaphthalene (DMN) with OH radicals were measured over the NO(2) concentration range 0.04-1.4 ppmv. The measured DMNN formation yields under conditions that the OH-DMN adducts reacted solely with NO(2) were 0.252 ± 0.094% for Σ1,7-DMNNs and 0.010 ± 0.005% for Σ2,7-DMNNs. 1,7-DM-5-NN was the major isomer formed, with a limiting high-NO(2) concentration yield of 0.212 ± 0.080% and with equal reactions of the adduct with NO(2) and O(2) occurring in air at 60 ± 39 ppbv of NO(2). The reactions of the OH-DMN adducts with NO(2) must therefore result in products other than DMNNs. Although the yields of the DMNNs are low, ≤0.3%, the DMNN (and ethylnitronaphthalene) profiles from chamber experiments match well with those observed in polluted urban areas under conditions where OH radical-initiated chemistry is dominant. Daytime OH radical and nighttime NO(3) radical reactions appear to account for the alkylnitronaphthalenes formed and their observed profiles under most urban atmospheric conditions, with profiles reflecting daytime OH chemistry modified by contributions from isomers formed by any NO(3) radical chemistry that had occurred. Since the formation yields and NO(2) dependencies for the formation of a number of alkylnitronaphthalenes have now been measured, the effect of NO(x) emissions control strategies on their atmospheric formation can be quantitatively assessed, and the decrease in formation of these genotoxic species may provide a previously unrecognized health benefit of NO(x) control.     

Influence of collagen and natural casings on the polycyclic aromatic hydrocarbons in traditional dry fermented sausage (Petrovská klobása) from Serbia

The aim of this study was to determine the content of polycyclic aromatic hydrocarbons—PAHs (acenaphthylene, anthracene, fluorene, phenanthrene, pyrene, benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, chrysene, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene, and benzo[ghi]perylene)—from Environmental Protection Agency list (United States Environmental Protection Agency) in traditional dry fermented sausage (Petrovská klobása) stuffed in collagen (C) and natural casings (N). Benzo[a]pyrene as well as PAH4 (benz[a]anthracene, benzo[b]fluoranthene, benzo[a]pyrene, and chrysene) were not detected in all examined samples. Results obtained in this study indicated that at the end of drying, as well as at the end of storage period, total content of 13 US-EPA PAH was significantly (P < 0.05) lower in sausages with collagen casing (56.2 and 73.6 μg/kg, respectively) than in sausages with natural casing (137.1 and 206.2 μg/kg, respectively).     

Substrate specificity of glutamyl endopeptidase (GE): Hydrolysis studies with a bovine α-casein preparation

Glutamyl endopeptidase (GE) from Alcalase™ 2.4 L was purified using hydrophobic interaction (HIC) and ion-exchange (IEX) chromatography. The yield of GE obtained was approximately 42%. Bovine α-casein (containing α_s1- and α_s2-casein) was digested with GE at 37 and 50 °C for 4 h. Samples were withdrawn at various time intervals and the peptides generated were analysed using mass spectrometry. GE activity was highly specific and hydrolysed the peptide bond predominantly on the carboxy side of Glu residues while hydrolysis on the carboxyl side of Asp residues was also observed. Hydrolysis did not occur when Pro was at the P₁′ position. In Glu-Glu-X (X = Arg, Asn, Ile and Ser) and Glu-Glu-Glu-Lys sequences, hydrolysis of Glu-X and Glu-Lys was preferred. The results are relevant to our understanding of the hydrolytic specificity of Alcalase, a food-grade proteolytic preparation containing GE activity which is used in the generation of casein hydrolysates.     

Natural chlorate in the environment: application of a new IC-ESI/MS/MS method with a Cl¹⁸O₃-internal standard

A new ion chromatography electrospray tandem mass spectrometry (IC-ESI/MS/MS) method has been developed for quantification and confirmation of chlorate (ClO??) in environmental samples. The method involves the electrochemical generation of isotopically labeled chlorate internal standard (Cl1?O??) using 1?O water (H?1?O) he standard was added to all samples prior to analysis thereby minimizing the matrix effects that are associated with common ions without the need for expensive sample pretreatments. The method detection limit (MDL) for ClO?? was 2 ng L?1 for a 1 mL volume sample injection. The proposed method was successfully applied to analyze ClO?? in difficult environmental samples including soil and plant leachates. The IC-ESI/MS/MS method described here was also compared to established EPA method 317.0 for ClO?? analysis. Samples collected from a variety of environments previously shown to contain natural perchlorate (ClO??) occurrence were analyzed using the proposed method and ClO?? was found to co-occur with ClO?? at concentrations ranging from < 2 ng L?1 in precipitation from Texas and Puerto Rico to >500 mg kg?1 in caliche salt deposits from the Atacama Desert in Chile. Relatively low concentrations of ClO?? in some natural groundwater samples (0.1 μg L?1) analyzed in this work may indicate lower stability when compared to ClO?? in the subsurface. The high concentrations ClO?? in caliches and soils (3-6 orders of magnitude greater) as compared to precipitation samples indicate that ClO??, like ClO??, may be atmospherically produced and deposited, then concentrated in dry soils, and is possibly a minor component in the biogeochemical cycle of chlorine.     

Efficient hydrolytic reaction of an acetate ester with fungal lipase in a liquid-liquid interface bioreactor (L-L IBR) using CaCO₃-coated ballooned microsphere

In a liquid-liquid interface bioreactor using a CaCO?-coated ballooned microsphere, 2-ethylhexyl acetate was efficiently hydrolyzed to 2-ethyl-1-hexanol with Absidia coerulea NBRC 4423 compared with using talc-coated or non-coated ballooned microsphere. It was assumed that CaCO? brought about stabilization of lipase by Ca2? and maintenance of medium pH.     

Nicotine determination in mushrooms by LC–MS/MS with preliminary studies on the impact of drying on nicotine formation

A problem concerning significant amounts of nicotine in dried wild mushrooms (mainly Boletus edulis from China) has been reported to the European Commission. As a consequence, the European Food Safety Authority (EFSA) proposed temporary maximum residue levels (MRLs) of 0.036 mg kg^?1 for fresh wild mushrooms and 1.17 mg kg^?1 for dried wild mushrooms (2.3 mg kg^?1 for dried ceps only). The EFSA also highlighted the necessity for a monitoring and testing programme to be launched by food business operators at the start of the 2009 harvest season. In the present study, a quick and sensitive analytical method for routine analysis of nicotine in fresh and dried mushrooms was developed and validated by a single-laboratory procedure. The method, which employs an LC–MS/MS system and (±)-nicotine-d ₄ as internal standard, has a limit of quantification of 6 and 60 µg kg^?1 for fresh and dried product, respectively. Analyses of samples spiked with different levels of nicotine showed recoveries ranging from 107 to 122%, with relative standard deviations of 2.9–10.1% depending on the spiking level. The combined uncertainties, calculated at a low level for frozen (0.015 mg kg^?1) and a high level for the dried (2 mg kg^?1) matrix, were 13 and 10%, respectively. Application of the method to real samples of mushrooms purchased on the market or obtained from local producers showed nicotine levels ranging 0.01–0.04 and 0.1–4.5 mg kg^?1 in fresh/frozen and dried matrices, respectively. To establish reasons for the unexpectedly high levels of the nicotine in dried matrices, preliminary laboratory experiments involving drying mushrooms were performed under various conditions.     

Rheological and textural studies of fresh and freeze-thawed native sago starch–sugar gels. II. Comparisons with other starch sources and reheating effects

The viscoelastic and textural properties of freshly prepared and freeze-thawed sago starch–sugar gels were studied in comparison with other native starches from corn, wheat, tapioca, and potato. The gelatinisation and retrogradation properties of starches were studied using a DSC while the pasting properties of starch–sugar mixtures during the cooking period were studied using a starch pasting cell. The freeze-thaw stability of gels was evaluated by gravimetric measurements of the water of syneresis. The different starches gave properties which varied following to their botanical sources. High-amylose cereal starches (wheat and corn) produced harder gels, while low-amylose root starch (tapioca) produced softer gels. Sago and potato gels showed close similarities in their viscoelastic and textural characteristics. Although the freeze-thaw cycle greatly increased the viscoelasticity and hardness of these two gels, reheating at high temperature significantly reduced these negative effects and resulted in partial recovery of the gel structures. Sago starch produced gels with very low syneresis and high cohesiveness, implying its potential use as a gelling agent in the frozen food industries.