Selective detection of nitrated polycyclic aromatic hydrocarbons by electrospray ionization mass spectrometry and constant neutral loss scanning

The development of a method for selective detection of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) among other polycyclic aromatic compounds (PACs) is described. The method is based on electrospray ionization mass spectrometry (ESI-MS), performed with a triple quadrupole analyzer and constant neutral loss (CNL) scanning. When subjected to ESI conditions, nitro-PAHs give rise to M(-), [M - H](-) and [M - H + 16](-) ions, which in turn produce fragments by losing 30 u, most probably NO. Other PACs do not undergo such fragmentations, and these differences can be exploited for selective detection of nitro-PAHs among other PACs. Nitro-PAHs can therefore be monitored through the loss of 30 u occurring under negative ion mode ESI conditions. Toward the full development of a screening method for nitro-PAHs, this article first discusses some general aspects of the negative ion mode full-scan ESI mass spectra obtained for these compounds and other PAH derivatives. Because the extent of observation of the loss of 30 u is sensitive to the ESI conditions used, the effects of ionization parameters such as solvent used, declustering voltage, and solvent flow rate are evaluated and discussed. Setting these parameters is very important, especially when interfacing a high performance liquid chromatography (HPLC) system with the ESI source of a triple quadrupole mass spectrometer. Preliminary results of on-line microbore HPLC/ESI-MS separations of PAC standards are presented, and elution/ionization conditions discussed.     

Determination of trace amounts of polycyclic aromatic hydrocarbons in soil

A method for monitoring the contamination of soil with polycyclic aromatic hydrocarbons (PAHs) is introduced. Drying at elevated temperature is omitted to avoid losses of the more volatile constituents (primarily naphthalene). The soil sample, including its natural water content, is extracted with 2-methoxyethanol and cleaned up using a disposable C₈ cartridge and the PAHs are eluted with pentane, concentrated and measured by capillary gas chromatography with flame ionization detection. Determination limits between 15 and 35μg kg^?1 are obtained and the recovery is 80–90% measured at the 125 μg kg^?1 spike level, except for naphthalene (66%). Special attention is given to the design of the spiking technique, which simulates natural incorporation as far as possible, takes account of evaporation losses and therefore allows “real” recovery rates to be determined.     

Coupled LC-GC-MS for on-line clean-up,separation, and identification of chlorinated polycyclic aromatic hydrocarbons at picogram levels in urban air

Coupled liquid chromatography – gas chromatography – mass spectrometry (LC-GC-MS) has been applied for on-line clean up, separation, and identification of chlorinated polycyclic aromatic hydrocarbons (CI-PAHs). A loop-type interface was used to couple the liquid chromatograph on-line with the GC-MS, and concurrent solvent evaporation was used for sample transfer. A back-flush technique was used in conjunction with a two-dimensional column system for isolation of CI-PAHs and polycyclic aromatic hydrocarbons (PAHs). This fraction was transferred on-line to the GC and separated on a capillary column. Selective and sensitive detection of CI-PAHs in the GC eluate was obtained by negative ion chemical ionization (NICI) mass spectrometry and selected ion monitoring (SIM). The combined on-line system for isolation, separation, and identification showed high precision and accuracy, and demonstrated a linear response from 1 to 1000 pg for chlorinated PAHs. The estimated detection limit was 250 fg for 1-chloropyrene and 1,6-dichloropyrene. The technique was demonstrated by analysis of urban air samples. The low detection limit made it possible to use the technique for analysis of personally carried monitoring equipment for measurement of exposure to CI-PAHs in the work environment.     

Determination of nitrated-polyaromatic hydrocarbons (nitro-PAHs) in environmental samples by high resolution chromatographic techniques

An analytical procedure is described for the fractionation of organic compounds present in environmental samples and the determination of nitro polyaromatic hydrocarbons (nitro-PAHs). Both low and high resolution liquid chromatography are employed for the prefractionation of the soluble organic fraction (SOF) extracted from particulate matter or gaseous pollutants collected on adsorption traps. High resolution gas chromatography is used to analyze four fractions containing alkanes, PAHs, nitro-PAHs, and other polar PAHs. Nitrogen-containing species are separated by GC and detected specifically using an alkali flame (NPD) detector. Flame ionization (FID) detection, GC-MS of positive ions, and negative ion chemical ionization MS of the whole fraction is used for the identification and quantitation of the various components. The composition of SOF extracted from particulate matter emitted from diesel exhausts is elucidated and a large number of nitro-PAHs identified by the combination of the various techniques.     

Unified Procedure for the Determination of Polycyclic Aromatic Hydrocarbons and Their Nitro Derivatives by Low-Temperature Luminescence

A method was described for determining polycyclic aromatic hydrocarbons (PAHs) and their nitro derivatives (nitro-PAHs) in samples of complex composition using low-temperature luminescence. Fractionation by HPLC was used to separate compounds with similar spectral properties. At the chromatograph inlet, a test sample was purified from weakly retained components additionally preconcentrated on a concentrator cartridge, which was fixed in the injector in place of the sampling loop. Step gradient fractionation was considered, and a table of retention times for PAHs and nitro-PAHs was presented. The the fractional distribution of the analytes was studied. Phosphorescence spectra of some nitro-PAHs were described. The method proposed is comparable in sensitivity to HPLC with the fluorescence detection, but does not require derivatization for determining nitro-PAHs. A table of spectral parameters of analytes suffices for qualitative analysis, as in chromatography–mass spectrometry. However, in distinction to the latter technique, the method described is selective because of the specificity of excitation and emission spectra of each of the analytes.     

Electrospray ionization mass spectrometric detection of low polar compounds by adding NaAuCl4

Liquid chromatography electrospray ionization mass spectrometry (LC/ESI/MS) has been widely used for various analyses. However, it is difficult to use LC/ESI/MS for the analysis of low polar compounds, such as polycyclic aromatic hydrocarbons. It is well known that AuCl₄^? ion decomposes to AuCl₃ by heating, and AuCl₃ is a strong π‐electrophilic Lewis acid. Low polar compounds (pyrene, benzo[a]pyrene, perylene, benzo[ghi]perylene, dibenzothiophene and p‐dimethoxybenzene) were detected by ESI/MS in the positive ion mode by adding NaAuCl₄. The low polar compound interacts with AuCl₃ formed at the ESI interface, and undergoes electron transfer to AuCl₃. The radical cation of the low polar compound was then detected by MS. In addition, the LC/ESI/MS determination of polycyclic aromatic hydrocarbons by the post‐column addition of NaAuCl₄ was studied. © 2016 The Authors Journal of Mass Spectrometry Published by John Wiley & Sons Ltd     

Efficient analysis of non-polar environmental contaminants by MALDI-TOF MS with graphene as matrix

In this Application Note, we describe, for the first time, the rapid analysis of hydrophobic compounds present in environmental contaminants, which includes polycyclic aromatic hydrocarbons (PAHs) and estrogen, by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with the use of graphene as matrix. MALDI-TOF MS with conventional matrix has limitations in analyzing low-polarity compounds owing to their difficulty in ionization. We demonstrate that compared with conventional matrix, graphene displays higher desorption/ionization efficiencies for PAHs, and no fragment ions are observed. The method also holds potential in quantitative analysis. In addition, the ionization signal increases with the increasing number of benzene rings in the PAHs, suggesting that graphene binds to PAHs via π–π stacking interactions. Furthermore, graphene as adsorbent for solid-phase extraction of coronene from river water sample displays good performance with a detection limit of 10^–7 M. This work provides a novel and convenient method for analyzing low-polarity environmental contaminants by MALDI-TOF MS.     

Analysis of organic pollutants in water at trace levels using fully automated solid-phase extraction coupled to high-performance liquid chromatography

Summary A method has been developed for the determination of trace levels of 32 pesticides, 19 explosives and 16 polycyclic aromatic hydrocarbons (PAH) in water in three individual steps. Solid-phase enrichment (SPE) is coupled to high-performance liquid chromatography (HPLC) with a fully automated system. The organic pollutants are enriched on reusable cartridges packed with adsorbent materials: pesticides and explosives on a mixed bed of divinylbenzene-ethylvinylbenzene copolymers (LiChrolut EN^?) and perfluorinated polyethylene (PolyF^?), and polycyclic aromatic hydrocarbons on C₁₈-modified silica (Zorbax^? ODS1). Thermally assisted desorption (TAD) has been shown to increase the recovery of analytes significantly. As all enriched analytes are transferred to the detector, only fifty millilitres of sample is needed for each single on-line analysis, compared with at least a litre for conventional methods. The separation of the enriched organic analytes is performed on specialized HPLC columns based on reversed-phase materials. The limits of detection of the system employed were found to be below 100 ng L⁻¹. Use of fluorescence detection for the polycyclic aromatic hydrocarbons resulted in limits of detection in the upper pg L⁻¹ range. Thek values, number of theoretical plates, the recovery rates and the limits of detection of this method for fast screening of organic pollutants from three fifty-millilitre aqueous samples are described. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

In-source fragmentation of partially oxidized mono- and polycyclic aromatic hydrocarbons in atmospheric pressure chemical ionization mass spectrometry coupled to liquid chromatography

Partially oxidized derivatives of polycyclic aromatic hydrocarbons (PAHs) are known to be important environmental pollutants. For the identification of these substances in complex mixtures, e.g. atmospheric aerosol samples, liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization (LC/APCI-MS) has been found to be a suitable analytical technique. In this study 31 derivatives of mono- and polycyclic aromatic hydrocarbons with up to five condensed aromatic rings carrying different functional groups (carboxyl, dicarboxylic anhydride, lactone, hydroxyl, and carbonyl) were characterized by LC/APCI-MS. Each substance was measured in positive and negative ion detection mode at four different fragmentor voltages (90 to 190 V). For the first time, the results show that characteristic and well-interpretable fragmentation patterns can be obtained for these classes of compounds by in-source collision-induced dissociation in a single quadrupole LC/APCI-MS system. For each class of compounds typical spectral features and optimum measurement conditions are reported, and fragmentation pathways are proposed. The study demonstrates the applicability of LC/APCI-MS for the determination of most of the investigated compounds at trace levels, and it provides a database for the identification of unknown partially oxidized aromatic hydrocarbons. Copyright 1999 John Wiley & Sons, Ltd.     

Determination of selected oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) in diesel and air particulate matter standard reference materials (SRMs)

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) have recently received much attention in discussions regarding the negative impacts of particulate matter (PM) on human health and the environment. The National Institute of Standards and Technology provides several environmental matrix standard reference materials (SRMs) with certified and reference values for polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs. In this study, the concentrations of oxygenated PAHs are determined in three air PM SRMs (1649b, 1648a, and 2786) and three diesel PM SRMs (1650b, 2975, and 1975) using two independent gas chromatography–mass spectrometry methods. Concentrations of oxy-PAHs were at the milligrams per kilogram level with higher overall concentrations in diesel PM (up to 50 mg/kg for 9,10-anthraquinone). One of the highest oxy-PAH concentrations (up to 5 mg/kg) measured in the air particulate SRMs was for 7,12-benz[a]anthracenquinone. These results suggest that oxygenated PAHs should not be neglected in the analysis of PM as their concentrations can be as high as those of some PAHs and are one to two orders of magnitude higher than those for nitro-PAHs.     

Gas chromatography–tandem mass spectrometry analysis of 52 monohydroxylated metabolites of polycyclic aromatic hydrocarbons in hairs of rats after controlled exposure

A method based on gas chromatography–tandem mass spectrometry after derivatization with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide was developed for the analysis of monohydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in hair. The method focused on 52 target compounds corresponding to two- to six-ring monohydroxylated metabolites of polycyclic aromatic hydrocarbons (PAHs). The limits of quantification ranged from 0.2 to 50 pg mg^?1. The method was then applied to the analysis of hair samples collected from rats exposed to 12 PAHs at 0.01, 0.1, and 1 mg kg^?1, by intraperitoneal injection, for 28 days. The results of this study confirm that these metabolites can be incorporated in hair after intraperitoneal administration of the corresponding parent compound. Only 20 of the 52 metabolites were actually detected in hair samples and corresponded to nine parent PAHs. The mean concentrations of OH-PAHs in rat hair samples exposed to PAHs at 1 mg kg^?1 ranged from 0.6?±?0.2 pg mg^?1 for 8-hydroxybenzo[b]fluoranthene to 6.7?±?1.0 pg mg^?1 for 1-hydroxypyrene. The results also demonstrated that hair pigmentation has no influence on the concentration of most OH-PAHs. This animal experiment confirmed the incorporation of PAH metabolites in hair and demonstrated that the method was sufficiently sensitive to detect low levels of exposure to PAHs. These results confirmed the usefulness of hair analysis in the biomonitoring of human exposure to PAHs.

Analysis of nitrated polycyclic aromatic hydrocarbons by glass capillary gas chromatography using different detectors

Glass capillary gas chromatography has been investigated as a method for the analysis of nitrated polycyclic aromatic hydrocarbons (nitro-PAH) using both splitless and on-column injection techniques. The nitro-PAH showed good chromatographic performance and thermal stability under the GC conditions used. Retention times and response factors of several nitro-PAH were compared to those of conventional PAH. Simultaneous flame ionization and thermionic nitrogen selective detection was used to facilitate identification of nitro-PAH in complex samples. The feasibility of the method is demonstrated on two samples of commercial carbon black. Besides 1-nitropyrene several isomeric dinitropyrenes have been identified.     

Polyaniline-coated magnetite nanoparticles incorporated in alginate beads for the extraction and enrichment of polycyclic aromatic hydrocarbons in water samples

A magnetic solid-phase extraction sorbent consisting of polyaniline-coated magnetite nanoparticles entrapped in alginate beads (PANI/alginate/Fe₃O₄) was successfully synthesised and applied for the extraction and preconcentration of polycyclic aromatic hydrocarbons (PAHs) in water samples. The magnetite nanoparticles helped to provide an easy and rapid isolation of the sorbent from the sample solution using an external magnet. The alginate beads helped to increase the surface area for polyaniline coating. The polyaniline-coated alginate/magnetite composite helped to increase the extraction efficiency due to the π–π interactions between the polyaniline and the PAHs. Various parameters that affected the extraction efficiencies were optimised including the polymerisation time, the amount of sorbent, sample pH, extraction time, ionic strength, and desorption conditions. Under the optimal conditions, a linear response was achieved in the concentration range of 0.040–50.0 µg L^?1, and the limit of detection was 0.010 µg L^?1. This simple, convenient, cost-effective, and environmentally friendly method was successfully applied for the extraction and enrichment of PAHs in water samples. The recoveries ranged from 86.0% to 97.8% with a relative standard deviation <10 %.     

Identification of oxygenated polycyclic aromatic hydrocarbons in diesel particulate matter by capillary gas chromatography and capillary gas chromatography/mass spectrometry

Summary Using a two-step liquid chromatographic separation on normalphase cartridges, crude extracts of diesel particulate matter can be separated without time-consuming sample handling into special fractions which mainly contain slightly-polar oxygenated polycyclic aromatic hydrocarbons (oxy-PAH) and nitrated polycyclic aromatic hydrocarbons (nitro-PAH). Subsequent analysis was by fused-silica capillary gas chromatography on a SE54 column along with flame-ionisation (GC/FID) and positive-ion electron-impact mass spectrometric detection (GC/MS) respectively. A number of individual oxy-PAH belonging to four different chemical classes (ketones, quinones, anhydrides and aldehydes) and several individual nitro-PAH were characterized by their retention times and mass spectra. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

GC�CMS Determination of PAHs in Fish Samples Following Salting-out-Assisted Solvent Extraction-Gel Permeation Chromatography

A fast and effective sample cleanup procedure for the quantification of polycyclic aromatic hydrocarbons (PAHs) in fish samples is presented. The procedure involved extraction of fish samples using acetonitrile and cleanup by an automated gel-permeation chromatography (GPC) following liquid?Cliquid partition into n-hexane. The extracted samples were analyzed by gas chromatography-mass spectrometry (GC?CMS). Electron ionization was employed in a single analysis for the determination of PAHs in the selected ion monitoring mode. Three different solvents were studied for the extraction step: acetonitrile/n-hexane, methanol/n-hexane and acetone/n-hexane. The best solvent was found to be acetonitrile/n-hexane. The cleanup technique resulted in a good separation of analytes from co-extractive matrix compounds.     

Determination of Polycyclic Aromatic Hydrocarbons in Tobacco Smoke by Ionic Liquid Enrichment and Gas Chromatography – Mass Spectrometry

A rapid, efficient and environmentally friendly method based on the ionic liquid (IL) 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in mainstream tobacco smoke. This technique combined ionic liquid (IL) enrichment with solvent reverse extraction for the replacement of solid phase extraction and rotary evaporation in the traditional method and enriched PAHs in the organic solvent. Several parameters, including the type of ionic liquid, volume of ionic liquid and water, extraction time, vortex time and reverse extraction time, were optimized. After pretreatment, the analytes were analyzed by gas chromatography-mass spectrometry (GC-MS) using selective ion monitoring (SIM). Satisfactory results were achieved when this method was applied to determine PAHs in mainstream tobacco smoke. The calibration curves were linear with correlation coefficients ranging from 0.9955 to 0.9999 at concentration levels of 10–800?µg?L^?1, and the relative standard deviations of the optimized method were between 0.7% and 5.3%. The limits of detection were 0.01–0.6?ng cig^?1, and the recoveries of the compounds were 80.2–118%. A comparison of this protocol with literature methods demonstrated that the proposed procedure provides accurate and reliable sample-treatment for the determination of PAHs in tobacco samples.     

Development of novel magnetic solid-phase extraction sorbent based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/carbon nanosphere/polypyrrole composite and their application to the enrichment of polycyclic aromatic hydrocarbons from water samples prior to GC–FID analysis

We describe a magnetic nanocomposite that consists of Fe₃O₄/carbon nanosphere/polypyrrole (Fe₃O₄/CNS/PPy). The synthesized nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The nanocomposite was successfully applied to extract of the polycyclic aromatic hydrocarbons (PAHs) from water samples. Compared to Fe₃O₄/PPy, the Fe₃O₄/CNS/PPy nanocomposite exhibits improved properties in terms of extraction. The amount of adsorbent, salt effect, extraction time, desorption time, type, and the volume of desorption solvent were optimized. Following the desorption of the extracted analytes, the PAHs (i.e., naphthalene, 2-methylnaphthalene, 2-bromonaphthalene, fluorene, and anthracene) were quantified by gas chromatography–flame ionization detector. The PAHs can be determined in 0.05–100.00 ng mL^?1 concentration range, with limits of detection (at an S/N ratio of 3) ranging from 0.01 to 0.05 ng mL^?1. The repeatability of the method was investigated with relative standard deviations of lower than 9.9% (n = 5). Also, the recoveries from spiked real water samples were in the range of 88.9–99.0%. The results indicate that the novel material can be successfully applied for the extraction and analysis of PAHs from water samples.     

Sensitive method for the determination of nitrated polycyclic aromatic hydrocarbons in the human diet

The presence of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) as contaminants in foods is nowadays a legitimate cause of concern, as they are reported to be strong direct-acting mutagens and carcinogens that may pose a risk to human health. Nevertheless, their concentrations in foods are in the ultra-trace region. In this study, we present a very sensitive analytical method for the determination of this compound class in complex food matrices. Special emphasis was put on sample extraction and clean up. Recoveries of 75% could be obtained for 1- and 2-nitronaphthalene; for all other compounds investigated the recoveries were >/=94%. The determination of the compounds was performed by gas chromatography-mass spectrometry. The results show that the use of negative chemical ionization (NCI) increases the sensitivity by one order of magnitude in comparison to electron impact ionization (EI) (limits of detection 0.07-0.25 micro g kg(-1) for EI and 0.01-0.02 micro g kg(-1) for NCI). The influence of the sample matrix on the sensitivity of the method is demonstrated with extracts of a sample from a duplicate diet study. Due to the lack of a certified reference material the suitability of the method is demonstrated with pumpkin seed oil that was spiked with nitro-PAHs at two different concentration levels.     

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.     

Atmospheric levels of polycyclic aromatic hydrocarbons in gas and particulate phases from Tarragona Region (NE Spain)

The atmospheric levels of polycyclic aromatic hydrocarbons (PAHs) in atmospheric samples taken at two urban sites and two sites near industrial areas of the Tarragona region (Catalonia, Spain), where one of the most important petrochemical complexes in the south of Europe is located, were determined. Gas and particulate phase of air were separately sampled and analysed. Concentrations of 16 PAHs studied ranged from 4.2 to 22.5 ng m^?3, with predominant levels of PAHs appearing in gas phase (～90% of total PAHs). In all samples, the most abundant compounds were phenanthrene, with a contribution to total PAHs between 32 and 44%, followed by naphthalene, fluorene and fluoranthene (contribution range: 10–22%). The levels of total PAHs, expressed as benzo[a]pyrene toxic equivalent factors (BaP_TEF), were lower than 0.06 ng m^?3.