Double molecular imprinting – a new sensor concept for improving selectivity in the detection of polycyclic aromatic hydrocarbons (PAHs) in water

It is now well recognised that the quality control (QC) of all types of analyses, including environmental analyses depends on the appropriate use of reference materials. One of the ways to check the accuracy of methods is based on the use of Certified Reference Materials (CRMs), whereas other types of (not certified) Reference Materials (RMs) are used for routine quality control (establishment of control charts) and interlaboratory testing (e.g. proficiency testing). The perception of these materials, in particular with respect to their production and use, differs widely according to various perspectives (e.g. RM producers, routine laboratories, researchers). This review discusses some critical aspects of RM use and production for the QC of environmental analyses and describes the new approach followed by the Measurements & Testing Generic Activity (European Commission) to tackle new research and production needs.     

Determination of selected polycyclic aromatic hydrocarbons and oxygenated polycyclic aromatic hydrocarbons in aerosol samples by high-performance liquid chromatography and liquid chromatography–tandem mass spectrometry

Fine and ultrafine particles are probably responsible for numerous health effects, but it is still unclear whether and to what extent the particle itself or organic compounds adsorbed or condensed on the particle are responsible for the effects observed. One important class of particle-bound substances are the polycyclic aromatic hydrocarbons (PAH) and their oxygenated derivatives. To improve the tools used for chemical characterization of particulate matter analytical methods for the determination of PAH and oxygenated PAH in aerosol samples of different origin have been developed and optimized. PAH on high-volume filters and on soot aerosols were analyzed by using accelerated solvent extraction for extraction and high-performance liquid chromatography with fluorescence detection for separation and quantification. Total PAH concentrations were in the range 0.3–9.3 ng m^–3. For analysis of selected oxygenated PAH on high-volume filters a liquid chromatography–tandem mass spectrometric method was developed and optimized. Preliminary investigations showed that oxygenated PAH at pg m^–3 concentrations can be determined.     

Molecules-in-molecule estimation of the extent of localization of Kekuléan substructures in polycyclic aromatic hydrocarbons

This article first revises graph-theoretical (local aromaticity and overall molecular) indices, introduced by M. Randi? in 1975, for benzenoid hydrocarbons and somewhat improves them for computer enumeration. This goes beyond total Kekulé structure enumeration, yielding an index calculation useful for the quantitative estimation of localization of different Kekuléan substructures (including ethylene-, benzene-, annulene-, and radialene-units). This may be viewed as a "molecules-in molecule" approach to polycyclic aromatic hydrocarbons within the context of graph theoretical partitioning.     

Implementation of comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry for the simultaneous determination of halogenated contaminants and polycyclic aromatic hydrocarbons in fish

In the presented study, comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC?×?GC-TOFMS) was shown to be a powerful tool for the simultaneous determination of various groups of contaminants including 18 polychlorinated biphenyls (PCBs), seven polybrominated diphenyl ethers (PBDEs), and 16 polycyclic aromatic hydrocarbons (PAHs). Since different groups of analytes (traditionally analyzed separately) were included into one instrumental method, significant time savings were achieved. Following the development of an integrated sample preparation procedure for an effective and rapid isolation of several groups of contaminants from fish tissue, the GC?×?GC-TOFMS instrumental method was optimized to obtain the best chromatographic resolution and low quantification limits (LOQs) of all target analytes in a complex mixture. Using large-volume programmable temperature vaporization, the following LOQs were achieved-PCBs, 0.01-0.25 μg/kg; PBDEs, 0.025-5 μg/kg; PAHs 0.025-0.5 μg/kg. Furthermore, several capillary column combinations (BPX5, BPX50, and Rxi-17Sil-ms in the first dimension and BPX5, BPX50, Rt-LC35, and HT8 in the second dimension) were tested during the experiments, and the optimal separation of all target analytes even of critical groups of PAHs (group (a): benz[a]anthracene, cyclopenta[cd]pyrene and chrysene; group (b): benzo[b]fluoranthene, benzo[j]fluoranthene and benzo[k]fluoranthene; group (c): dibenz[ah]anthracene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene) was observed on BPX5?×?BPX50 column setup. Moreover, since the determination of target analytes was performed using TOFMS detector, further identification of other non-target compounds in real life samples was also feasible.     

Homogeneous liquid–liquid microextraction via flotation assistance for rapid and efficient determination of polycyclic aromatic hydrocarbons in water samples

In this work, a rapid, simple and efficient homogeneous liquid–liquid microextraction via flotation assistance (HLLME-FA) method was developed based on applying low density organic solvents without no centrifugation. For the first time, a special extraction cell was designed to facilitate collection of the low-density solvent extraction in the determination of four polycyclic aromatic hydrocarbons (PAHs) in water samples followed by gas chromatography-flame ionization detector (GC-FID). The effect of different variables on the extraction efficiency was studied simultaneously using experimental design. The variables of interest in the HLLME-FA were selected as extraction and homogeneous solvent volumes, ionic strength and extraction time. Response surface methodology (RSM) was applied to investigate the optimum conditions of all the variables. Using optimized variables in the extraction process, for all target PAHs, the detection limits, the precisions and the linearity of the method were found in the range of 14–41 μg L⁻¹, 3.7–10.3% (RSD, n = 3) and 50–1000 μg L⁻¹, respectively. The proposed method has been successfully applied to the analysis of four target PAHs in the water samples, and satisfactory results were obtained.     

Exploration of the π-electronic structure of singlet, triplet, and quintet states of fulvenes and fulvalenes using the electron localization function

The singlet ground states and lowest triplet states of penta- and heptafulvene, their benzannulated derivatives, as well as the lowest quintet states of pentaheptafulvalenes, either the parent compound or compounds in which the two rings are intercepted by either an alkynyl or a phenyl segment, were investigated at the (U)OLYP/6-311G(d,p) density functional theory level. The influence of (anti)aromaticity was analyzed by the structure-based aromaticity index HOMA, the harmonic oscillator model of aromaticity. The extent of (anti)aromatic character was also evaluated in terms of the π-electron (de)localization as measured by the π component of the electron localization function (ELF(π)). The natural atomic orbital (NAO) occupancies were calculated in order to evaluate the degree of π-electron shift caused by the opposing electron-counting rules for aromaticity in the electronic ground state (S(0); Hückel's rule) and the first ππ* excited triplet state (T(1); Baird's rule). Pentaheptafulvalene (5) shows a shift of 0.5 π electrons from the 5-ring to the 7-ring when going from the S(0) state to the lowest quintet state (Qu(1)). The pentaheptafulvalene 5 and [5.6.7]quinarene 7 were also investigated in their 90° twisted conformations. From our study it is apparent that excitation localization in fulvalenes, but not in fulvenes, to a substantial degree is determined by aromaticity localization to triplet biradical 4n π-electron cycles. Isolated benzene rings in these compounds tend to remain as closed-shell 6π-electron cycles.     

Development of an ionic liquid based dispersive liquid–liquid microextraction method for the analysis of polycyclic aromatic hydrocarbons in water samples

A simple, rapid and efficient method, ionic liquid based dispersive liquid–liquid microextraction (IL-DLLME), has been developed for the first time for the determination of 18 polycyclic aromatic hydrocarbons (PAHs) in water samples. The chemical affinity between the ionic liquid (1-octyl-3-methylimidazolium hexafluorophosphate) and the analytes permits the extraction of the PAHs from the sample matrix also allowing their preconcentration. Thus, this technique combines extraction and concentration of the analytes into one step and avoids using toxic chlorinated solvents. The factors affecting the extraction efficiency, such as the type and volume of ionic liquid, type and volume of disperser solvent, extraction time, dispersion stage, centrifuging time and ionic strength, were optimised. Analysis of extracts was performed by high performance liquid chromatography (HPLC) coupled with fluorescence detection (Flu). The optimised method exhibited a good precision level with relative standard deviation values between 1.2% and 5.7%. Quantification limits obtained for all of these considered compounds (between 0.1 and 7 ng L⁻¹) were well below the limits recommended in the EU. The extraction yields for the different compounds obtained by IL-DLLME, ranged from 90.3% to 103.8%. Furthermore, high enrichment factors (301–346) were also achieved. The extraction efficiency of the optimised method is compared with that achieved by liquid–liquid extraction. Finally, the proposed method was successfully applied to the analysis of PAHs in real water samples (tap, bottled, fountain, well, river, rainwater, treated and raw wastewater).     

The acid—base equilibria of dimethylphenols in the ground and the first excited singlet states

Measurements of the acidity constants in the ground (pK_a(S₀)) and the lowest excited singlet (pK_a(S₁)) states for 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dimethylphenols in aqueous solution have been carried out spectrophotometrically at 25°C. The pK_a values in S₀ have been derived from the absorption spectra and the pK_a values in S₁ were estimated by means of the Forster cycle. It is found that the hydroxy group is more acidic in the first excited singlet than in the ground state.     

Application of an automatic thermal desorption–gas chromatography–mass spectrometry system for the analysis of polycyclic aromatic hydrocarbons in airborne particulate matter

The application of the thermal desorption (TD) method coupled with gas chromatography–mass spectrometry (GC–MS) to the analysis of aerosol organics has been the focus of many studies in recent years. This technique overcomes the main drawbacks of the solvent extraction approach such as the use of large amounts of toxic organic solvents and long and laborious extraction processes. In this work, the application of an automatic TD–GC–MS instrument for the determination of particle-bound polycyclic aromatic hydrocarbons (PAHs) is evaluated. This device offers the advantage of allowing the analysis of either gaseous or particulate organics without any modification. Once the thermal desorption conditions for PAH extraction were optimised, the method was verified on NIST standard reference material (SRM) 1649a urban dust, showing good linearity, reproducibility and accuracy for all target PAHs. The method has been applied to PM10 and PM2.5 samples collected on quartz fibre filters with low volume samplers, demonstrating its capability to quantify PAHs when only a small amount of sample is available.     

A headspace solid-phase microextraction procedure coupled with gas chromatography–mass spectrometry for the analysis of volatile polycyclic aromatic hydrocarbons in milk samples

A sensitive and solvent-free method for the determination of ten polycyclic aromatic hydrocarbons, namely, naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene and chrysene, with up to four aromatic rings, in milk samples using headspace solid-phase microextraction and gas chromatography–mass spectrometry detection has been developed. A polydimethylsiloxane–divinylbenzene fiber was chosen and used at 75°C for 60 min. Detection limits ranging from 0.2 to 5 ng L⁻¹ were attained at a signal-to-noise ratio of 3, depending on the compound and the milk sample under analysis. The proposed method was applied to ten different milk samples and the presence of six of the analytes studied in a skimmed milk with vegetal fiber sample was confirmed. The reliability of the procedure was verified by analyzing two different certified reference materials and by recovery studies. Figure Milk is safe, healthy food     

Ultrasonication extraction and gel permeation chromatography clean-up for the determination of polycyclic aromatic hydrocarbons in edible oil by an isotope dilution gas chromatography–mass spectrometry

An analytical method for the determination of US EPA priority pollutant 16 polycyclic aromatic hydrocarbons (PAHs) in edible oil was developed by an isotope dilution gas chromatography–mass spectrometry (GC–MS). Extraction was performed with ultrasonication mode using acetonitrile as solvent, and subsequent clean-up was applied using narrow gel permeation chromatographic column. Three deuterated PAHs surrogate standards were used as internal standards for quantification and analytical quality control. The limits of quantification (LOQs) were globally below 0.5 ng/g, the recoveries were in the range of 81–96%, and the relative standard deviations (RSDs) were lower than 20%. Further trueness assessment of the method was also verified through participation in international cocoa butter proficiency test (T0638) organised by the FAPAS with excellent results in 2008. The results obtained with the described method were satisfying (z ≤ 2). The method has been applied to determine PAH in real edible oil samples.     

Ultrasound-assisted extraction and on-line LC–GC–MS for determination of polycyclic aromatic hydrocarbons (PAH) in urban dust and diesel particulate matter

A method has been developed for determination of polycyclic aromatic hydrocarbons (PAH) in particulate matter from ambient air and diesel exhaust emissions. It is reproducible and accurate and, compared with similar methods for analysis of individual PAH components in complex matrices, it is relatively fast and simple. Single PAH components can be determined in samples of particulate matter from ambient air and diesel exhaust emissions with LOD of approximately 1 pg/sample. Further, sample throughput is high, because more than 20 samples can be extracted and prepared for analysis in one working (8-h) day. The particulate matter is subjected to ultrasound-assisted extraction, a technique that is shown to extract PAH from particulate material with efficiencies fully comparable with those of Soxhlet extraction. An aliphatic/PAH-enriched fraction is obtained by solid-phase extraction before isolation, separation, and identification/quantification of PAH by on-line liquid chromatography–gas chromatography–mass spectrometry. The method was validated by analysis of US National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) 1649a, Urban Dust, and 2975, Diesel Particulate Matter. Results from the method are in good agreement with the NIST-certified PAH concentrations and with NIST reference PAH concentrations.     

What accounts for the difference between singlet phenylphosphinidene and singlet phenylnitrene in reactivity toward ring expansion?

(8/8)CASSCF and (8/8)CASPT2 calculations have been performed in order to investigate the potential surface for the ring expansion of the (1)A(2) state of phenylphosphinidene (1c) to 1-phospha-1,2,4,6-cycloheptatetraene (3c). Unlike the comparable ring expansion of the (1)A(2) state of phenylnitrene (1b) to 1-aza-1,2,4,6-cycloheptatetraene (3b), ring expansion of 1c to 3c is computed to be quite endothermic. Nevertheless, cyclization of 1c, to form the bicyclic intermediate 2c in the ring expansion reaction, is computed to be only slightly more endothermic than the comparable cyclization reaction of 1b to 2b. The origins of these differences between the ring expansion reactions of 1b and 1c have been elucidated through the calculation of the energies of relevant isodesmic reactions.     

Chemometrics-assisted excitation–emission fluorescence spectroscopy on nylon-attached rotating disks. Simultaneous determination of polycyclic aromatic hydrocarbons in the presence of interferences

This work presents a green and very simple approach which enables the accurate and simultaneous determination of benzo[a]pyrene, dibenz[a,h]anthracene, benz[a]anthracene, and chrysene, concerned and potentially carcinogenic heavy-polycyclic aromatic hydrocarbons (PAHs) in interfering samples. The compounds are extracted from water samples onto a device composed of a small rotating Teflon disk, with a nylon membrane attached to one of its surfaces. After extraction, the nylon membrane containing the concentrated analytes is separated from the Teflon disk, and fluorescence excitation–emission matrices are directly measured on the nylon surface, and processed by applying parallel factor analysis (PARAFAC), without the necessity of a desorption step. Under optimum conditions and for a sample volume of 25 mL, the PAHs extraction was carried out in 20 min. Detection limits based on the IUPAC recommended criterion and relative errors of prediction were in the ranges 20–100 ng L⁻¹ and 5–7%, respectively. Thanks to the combination of the ability of nylon to strongly retain PAHs, the easy rotating disk extraction approach, and the selectivity of second-order calibration, which greatly simplifies sample treatment avoiding the use of toxic solvents, the developed method follows most green analytical chemistry principles.     

Transport method for determining the association constants of complexes formed between aromatic hydrocarbons andα- andβ-cyclodextrin in water

The association constants of 1 : 1 complexes formed in water between six aromatic hydrocarbons (o-,m-, andp-xylene, naphthalene, anthracene, and pyrene) and- and-cyclodextrin were determined by the transport method. The values are in good agreement with those determined by other methods.     

Flow injection solid-phase extraction using multi-walled carbon nanotubes packed micro-column for the determination of polycyclic aromatic hydrocarbons in water by gas chromatography–mass spectrometry

A flow injection solid-phase extraction preconcentration system using a multi-walled carbon nanotubes (MWCNTs) packed micro-column was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in water by gas chromatography–mass spectrometry (GC–MS). The preconcentration of PAHs on the MWCNTs was carried out based on the adsorption retention of analytes by on-line introducing the sample into the micro-column system. Methanol was introduced to elute the retained analytes for GC–MS analysis using selected ion monitoring (SIM) mode. Important influence factors were studied in detail, such as sample acidity, sample flow rate, eluent flow rate and volume, dimensions of MWCNTs and amounts of packing material. Limits of detection of 16 PAHs for an extraction of 50 mL water sample were in the range of 0.001–0.15 μg L⁻¹, and the precisions (RSD) were in the range of 4–14%. The optimized method was successfully applied to the determination of 16 PAHs in surface waters, with recoveries in the range of 72–93% for real spiked sample.     

Detection of the singlet and triplet MM δδ* states in quadruply bonded dimetal tetracarboxylates (M = Mo, W) by time-resolved infrared spectroscopy

The compounds M(2)(O(2)C(t)Bu)(4) and M(2)(O(2)CC(6)H(5))(4), where M = Mo or W, have been examined by femtosecond time-resolved IR (fs-TRIR) spectroscopy in tetrahydrofuran with excitation into the singlet metal-to-ligand charge-transfer ((1)MLCT) band. In the region from 1500 to 1600 cm(-1), a long-lived excited state (>2 ns) has been detected for the compounds M(2)(O(2)C(t)Bu)(4) and Mo(2)(O(2)C-C(6)H(5))(4) with an IR absorption at ~1540 cm(-1) assignable to the asymmetric CO(2) stretch, ν(as)(CO(2)), of the triplet metal-metal δ-δ star ((3)MM δδ*) state. The fs-TRIR spectra of W(2)(O(2)C-C(6)H(5))(4) are notably different and are assigned to decay of the MLCT states. In (3)MM δδ*, the removal of an electron from the δ orbital reduces MM δ to CO(2) π* back-bonding and causes a shift of ν(as)(CO(2)) to higher energy by ~30-60 cm(-1), depending on the metal. TRIR spectroscopy also provides evidence for M(2)(O(2)C(t)Bu)(4), where M = Mo or W, having MM δδ* S(1) states with ν(as)(CO(2)) distinct from those of the (3)MM δδ* states.     

Determination of hydroxylated metabolites of polycyclic aromatic hydrocarbons in sediment samples by combining subcritical water extraction and dispersive liquid–liquid microextraction with derivatization

A sample preparation method for the determination of hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in sediment samples was developed using gas chromatography–mass spectrometry (GC–MS). Dispersive liquid–liquid microextraction (DLLME) with derivatization was performed following the subcritical water extraction (SWE) that provided which was provided by accelerated solvent extraction (ASE). Several important parameters that affected both SWE extraction and DLLME, such as the selection of organic modifier, its volume, extraction temperature, extraction pressure and extraction time were also investigated. High sensitivity of the hydroxylated PAHs derivatives by N-(tert-butyldimethylsilyl)-N-methyl-trifluoroacetamide (MTBSTFA) could be achieved with the limits of detection (LODs) ranging from 0.0139 (2-OH-nap) to 0.2334 μg kg⁻¹ (3-OH-fluo) and the relative standard deviations (RSDs) between 2.81% (2-OH-phe) and 11.07% (1-OH-pyr). Moreover, the proposed method was compared with SWE coupled with solid phase extraction (SPE), and the results showed that ASE–DLLME was more promising with recoveries ranging from 57.63% to 91.07%. The proposed method was then applied to determine the hydroxylated metabolites of phenanthrene in contaminated sediments produced during the degradation by two PAH-degraders isolated from mangrove sediments.