Gas chromatographic determination of polycyclic aromatic compounds with fluorinated analogues as internal standards

Regiospecifically Fluorinated Polycyclic Aromatic Hydrocarbons via Julia-Kocienski Olefination and Oxidative Photocyclization. Effect of Fluorine Atom Substitution on Molecular Shape

A modular synthesis of regiospecifically fluorinated polycyclic aromatic hydrocarbons (PAHs) is described. 1,2-Diarylfluoroalkenes, synthesized via Julia-Kocienski olefination (70-99% yields), were converted to isomeric 5- and 6-fluorobenzo[c]phenanthrene, 5-and 6-fluorochrysene, and 9- and 10-benzo[g]chrysene (66-83% yields) by oxidative photocyclization. Photocyclization to 6-fluorochrysene proceeded more slowly than conversion of 1-styrylnaphthalene to chrysene. Higher fluoroalkene dilution led to a more rapid cyclization. Therefore, photocyclizations were performed at higher dilutions. To evaluate the effect of fluorine atom on molecular shapes, X-ray data for 5- and 6-fluorobenzo[c]phenanthrene, 6-fluorochrysene, 9- and 10-fluorobenzo[g]chrysene, and unfluorinated chrysene as well as benzo[g]chrysene were obtained and compared. The fluorine atom caused a small deviation from planarity in the chrysene series and decreased nonplanarity in the benzo[c]phenanthrene derivatives, but its influence was most pronounced in the benzo[g]chrysene series. A remarkable flattening of the molecule was observed in 9-fluorobenzo[g]chrysene, where the short 2.055 Å interatomic distance between bay-region F-9 and H-8, downfield shift of H-8, and a 26.1 Hz coupling between F-9 and C-8 indicate a possible F-9···H-8 hydrogen bond. In addition, in 9-fluorobenzo[g]chrysene, the stacking distance is short at 3.365 Å and there is an additional interaction between the C-11-H and C-10a of a nearby molecule that is almost perpendicular.

Analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples: a critical review of gas chromatographic (GC) methods

Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC), is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS), and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption, fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate the vigor and robustness GC continues to achieve in the analytical sciences.

Simple and sensitive determination of o-phenylphenol in citrus fruits using gas chromatography with atomic emission or mass spectrometric detection

In this work, a simple and sensitive method for the analysis of the pesticide o-phenylphenol (OPP) on citrus fruits was developed. OPP is extracted with dichloromethane by ultrasonication and derivatized with ferrocenecarboxylic acid chloride. Using ferrocene as a label, residues of OPP are determined by gas chromatography with atomic emission detection in the iron selective mode or with mass spectrometric detection. Sample cleanup is simple and rapid and merely involves a removal of excess reagent on an alumina minicolumn. The method detection limit is 2 ng of OPP/g of fruit, and recoveries from lemon samples fortified at levels of 35 and 140 ng/g are 101 and 106%, respectively. The citrus fruits analyzed (oranges, grapefruits, lemons) contained between 60 ng/g and 0.37 microg/g OPP (RSD = 8-13%), and the results were in good agreement with results obtained when OPP was analyzed using an established HPLC-FLD method. Several alcohols could also be identified in the fruit peel.

Characterization of monofluorinated polycyclic aromatic compounds by 1H, 13C and 19F NMR spectroscopy

Monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) have attracted much attention in analytical, environmental, toxicological and mechanistic studies because of their physico-chemical properties, which are closely similar to those of the parent PAHs. Because of this, full NMR characterization has become of interest. Complete 1H, 13C and 19F NMR chemical shifts, and also 1J(H,C), (n)J(C,F), (n)J(H,F) and (n)J(H,H) coupling constants, have been assigned for the F-PAHs 1-fluoronaphthalene, 2-fluorofluorene, 5-fluoroacenaphthylene, 2-fluorophenanthrene, 3-fluorophenanthrene, 3-fluorofluoranthene, 1-fluoropyrene, 1-fluorochrysene, 2-fluorochrysene, 3-fluorochrysene and 9-fluorobenzo[k]fluoranthene. To allow comparison with the corresponding parent PAHs, the 1H and 13C chemical shifts of acenaphthylene, phenanthrene, fluoranthene, pyrene and benzo[k]fluoranthene were determined. Chemical shift increments and the effects on the coupling constants from the fluorine substitution are discussed.

Monofluorinated polycyclic aromatic hydrocarbons as internal standards to monitor trace enrichment and desorption of their parent compounds during solid-phase extraction

Solid-phase extraction (SPE) is an established sample-preparation technique for clean-up procedures of polycyclic aromatic hydrocarbons (PAHs). The suitability of monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) as a novel set of internal standards, was tested for two widely used SPE sorbents, octyl-bonded silica and styrene-divinylbenzene copolymer. The elution profiles of eight F-PAHs and their parent PAHs, taken from the priority pollutant list of the US-Environmental Protection Agency, were compared for demineralized water and waste water. In both instances, the match of the elution profiles was exceptionally close. The eight F-PAHs and the corresponding PAHs were determined by reversed-phase liquid chromatography using acetonitrile-water gradient elution with UV detection at 254 nm. The UV spectra of the F-PAHs show a small bathochromic shift compared with the parent PAHs.

Determination of coal tar and creosote constituents in the aquatic environment

Creosote and its parent material, coal tar, are complex mixtures. Upon release their components fractionate into the air, water, soil/sediment and biota; as a function of their physical and chemical properties. Therefore, assessment of their fate and concentrations in the environment must consider a wide variety of both compounds and matrices. Analyses are typically complicated, consisting of sample extraction, purification and chromatography-based final characterization steps. Several new techniques have been introduced to reduce or simplify the number of steps, solvent and time required. Recently developed extraction methods include supercritical fluid, accelerated solvent, microwave and solid-phase microextraction. On-line purification and coupling of extraction and chromatography have also emerged. HPLC and GC remain the major tools for performing the final separations. Application of mass spectrometry has increased as more reliable, versatile and less expensive units have become available, such as the ion trap and mass selective detectors. Fluorescence and diode array UV, in concert with HPLC, and C-, S- and N-selective gas chromatographic detectors are also being applied.

Determination of 1-benzo[b]thien-2-ylethanone and related impurities by high performance liquid chromatography

1-Benzo[b]thien-2-ylethanone (2-acetylbenzothiophene, 2-ABT) and related impurities were determined using a reverse-phase high performance liquid chromatography system and UV detection at 254 nm. Separation was achieved isocratically on a 4.6 mm x 25 cm, 5 microns Zorbax Rx-C8 column using an eluent which is 0.2% perchloric acid/THF in a ratio of 60:40 (v/v). The chromatographic system resolved 2-ABT and known impurities in less than 45 min with near baseline resolution. Known impurities were quantitated versus 2-ABT with corrections made for differences in detector response at the specified wavelength. Linearity for 2-ABT was demonstrated with a correlation coefficient > 0.9999. Assay precision (RSD values) for impurities at 0.5% ranged from +/- 1.8% to +/- 14%, while precision (RSD values) for the 2-ABT determination ranged from +/- 0.81% to +/- 1.1%. A variety of different chromatographic columns and conditions are discussed for the application.