Examination of dodecylpyridinium chloride as a potentially selective fluorescence quenching agent for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons

Fluorescence behavior is reported for 13 alternant and 12 nonalternant polycyclic aromatic hydrocarbons (PAHs) dissolved in aqueous micellar cetyltrimethylammonium chloride (CTAC)+dodecylpyridinium chloride (DDPC) and sodium dodecylsulfate (SDS)+DDPC mixed surfactant solvent media. Experimental measurements indicate that the dodecylpyridinium cation selectively quenches fluorescence emission of alternant PAHs. Emission intensities of nonalternant PAHs, with a few noted exceptions, essentially remain constant, irrespective of both DDPC concentration and cosurfactant headgroup charge.     

Spectrochemical investigations in molecularly organized solvent media: evaluation of pyridinium chloride as a selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in aqueous carboxylate-terminated poly(amido) amine dendrimers and anionic micelles

The ability of pyridinium chloride (PC) to selectively quench alternant as opposed to nonaltemant polycyclic aromatic hydrocarbons (PAHs) in organized media is examined. PC was previously shown to be a selective quenching agent of alternant PAHs in neat polar solvents. Carboxylate-terminated poly(amido) amine (PAMAM-CT) dendrimers and anionic surfactants--sodium dodecanoate (SD), sodium octanoate (SO), and sodium dodecylsulfate (SDS)--were chosen as the solubilizing media for this study. Selective quenching of alternant PAHs is observed in the presence of the SDS and SO micelles. However, the extent of PAH quenching in SO is significantly reduced compared to PAHs dissolved in either water or SDS micelles. In the case of the smaller generation 4.5 (G4.5) PAMAM-CT dendrimers, PC was prevented from quenching both alternant and nonalternant PAHs to any appreciable extent. The dendrimer is able to "protect" the PAHs from the PC quencher that resides at the dendrimer surface. Both, SD and G5.5 PAMAM-CT precipitated out of solution with the addition of PC. Differences between traditional micelles and "unimolecular micelle" dendrimers were also examined. These studies further confirm that the PAHs did not reside in the "analogous" palisade region of the dendrimers as they do in micelles. The PAHs must reside in the outermost branches of the dendrimer, but sufficiently far enough away from the charged surface groups, where PC associated, to prevent fluorescence quenching. This work further illustrates the differences between "unimolecular micelle" dendrimers and traditional micelles.     

Spectrochemical investigations in molecularly organized solvent media: evaluation of pyridinium chloride as a selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in aqueous carboxylate-terminated poly(amido) amine dendrimers and anionic micelles

The ability of pyridinium chloride (PC) to selectively quench alternant as opposed to nonalternant polycyclic aromatic hydrocarbons (PAHs) in organized media is examined. PC was previously shown to be a selective quenching agent of alternant PAHs in neat polar solvents. Carboxylate-terminated poly(amido) amine (PAMAM-CT) dendrimers and anionic surfactants – sodium dodecanoate (SD), sodium octanoate (SO), and sodium dodecylsulfate (SDS) – were chosen as the solubilizing media for this study. Selective quenching of alternant PAHs is observed in the presence of the SDS and SO micelles. However, the extent of PAH quenching in SO is significantly reduced compared to PAHs dissolved in either water or SDS micelles. In the case of the smaller generation 4.5 (G4.5) PAMAM-CT dendrimers, PC was prevented from quenching both alternant and nonalternant PAHs to any appreciable extent. The dendrimer is able to “protect” the PAHs from the PC quencher that resides at the dendrimer surface. Both, SD and G5.5 PAMAM-CT precipitated out of solution with the addition of PC. Differences between traditional micelles and “unimolecular micelle” dendrimers were also examined. These studies further confirm that the PAHs did not reside in the “analogous” palisade region of the dendrimers as they do in micelles. The PAHs must reside in the outermost branches of the dendrimer, but sufficiently far enough away from the charged surface groups, where PC associated, to prevent fluorescence quenching. This work further illustrates the differences between “unimolecular micelle” dendrimers and traditional micelles. Received: 27 July 2000 / Revised: 25 September 2000 / Accepted: 27 September 2000     

Characterization of polycyclic aromatic hydrocarbons in environmental samples by selective fluorescence quenching

Selective fluorescence quenching is used to profile polycyclic aromatic hydrocarbons (PAHs) in samples of environmental origin. After separation by high-efficiency capillary liquid chromatography, the PAHs are detected by laser-induced fluorescence spectroscopy. Nitromethane is added to selectively quench the fluorescence of alternant PAHs, whereas diisopropylamine is added to quench nonalternant PAHs. The chromatograms in the absence and presence of fluorescence quenching are evaluated by means of the product moment correlation method to quantify the statistical similarities and differences. This method is demonstrated by application to three samples: a standard mixture of 16 priority pollutants, a coal-derived fluid, and a contaminated soil. The correlation coefficients (r) are typically 0.99 or higher for samples that are identical in origin, 0.90-0.50 for closely related samples, and less than 0.50 for samples that are distinctly unrelated. This method can be used to confirm with high statistical confidence the cause or source of an event with environmental impact, such as an oil leak or spill, contamination or waste by-products from petroleum fuel production and processing, etc.     

Spectrochemical evaluation of pyridinium chloride as a possible selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in water and neat acetonitrile

Pyridinium chloride (PC) is examined as a selective, fluorescence quenching agent for alternant as opposed to nonalternant polycyclic aromatic hydrocarbons (PAHs) in two polar solvents - water and acetonitrile. Nine alternant and 13 nonalternant PAHs were dissolved in water and acetonitrile and a total of 0.2 M of pyridinium chloride was added. The resulting change in fluorescence intensity was observed and reported as the Stern-Volmer quenching constant. Results show that PC is a selective quencher in both polar solvents. It selectively quenches the fluorescence emission intensity of alternant PAHs while leaving the nonalternant PAH fluorescence emission virtually unchanged. These results agree with the selective quenching behavior seen for PC surfactant analogs, cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DDPC). Furthermore, these results illustrate that the presence of a surfactant or micelle is not a requirement for selective quenching. The selective quencher PC is applicable to situations where a surfactant is not desirable or soluble.     

High-performance liquid chromatographic separation of polycyclic aromatic hydrocarbons using pyridinium chloride as a selective fluorescence quencher to aid detection

Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in dicloromethane. These results were in accordance with the intrinsic viscosity values of the PSF-solvent systems. The variation of A values with the Arocy B10 concentration is strongly dependent upon the nature of the solvent.     

Micellar liquid chromatography of polycyclic aromatic hydrocarbons: Alkylpyridinium chloride as mobile phase modifier and selective fluorescence quencher

The dual role of alkylpyridinium chlorides, cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DDPC), as micellar mobile phase modifiers and selective fluorescence quenching agents of polycyclic aromatic hydrocarbons (PAHs), in micellar liquid chromatographic separation of PAHs is reported. The replacement of 0.037 M cetyltrimethylammonium chloride in the aqueous mobile phase with CPC/DDPC quencher greatly simplifies the observed fluorescence‐detected chromatograms, facilitating PAH identification. The resulting chromatograms are similar to those obtained from the conventional approach – pyridinium chloride quencher in an acetonitrile mobile phase. To quantify the quenching, the (F₀ /F – 1) values from the Stern‐Volmer equation are calculated from the chromatograms and compared. The feasibility of using CPC or DDPC as a dual reagent under isocratic and gradient conditions is shown.     

Orientation effects in fluorescence quenching for adsorbed aromatic hydrocarbons

Fluorescence quenching by a potential electron donor or acceptor has been examined for an aromatic hydrocarbon adsorbed on aerosil, for which unusual temperature effects have been observed, where the process is dependent on the nature of the quencher. These phenomena are examined in terms of reaction stereospecificity. By this is meant the resultant displacement from a series of jumps between localization positions. Surface Chemistry Institute, Ukrainian National Academy of Sciences, Prospekt Nauki 31, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 12–16, January–February, 1997.     

Admicelle-enhanced synchronous fluorescence spectrometry for the selective determination of polycyclic aromatic hydrocarbons in water

A simple and rapid method for the highly sensitive determination of polycyclic aromatic hydrocarbons (PAHs) in water was developed. Benzo[a]pyrene, benzo[k]fluoranthene, perylene, and pyrene in water were concentrated into sodium dodecyl sulfate (SDS)-alumina admicelles. The collection was performed by adding SDS and alumina particles into the sample solution at pH 2. After gentle mixing, the resulting suspension was passed through a membrane filter to collect the SDS admicelles containing highly concentrated PAHs. The filter was placed on a slide glass and then covered admicellar layer with a fused silica glass plate before setting in a fluorescence spectrometer. Benzo[a]pyrene, benzo[k]fluoranthene, perylene, and pyrene were selectively determined by the synchronous fluorescence scan (SFS) analysis with keeping wavelength intervals between excitation and emission to 98, 35, 29, and 45 nm, respectively. Because of the minimum spectral overlapping, 1-40 ng l⁻¹ of benzo[a]pyrene, benzo[k]fluoranthene, and perylene as well as 10-150 ng l⁻¹ of pyrene were selectively determined with eliminating the interferences of other 12 PAHs. The detection limits were 0.3 ng l⁻¹ for benzo[a]pyrene, benzo[k]fluoranthene, and perylene, and 1 ng l⁻¹ for pyrene. They were 2-3 orders of magnitude lower than the detection limits in normal aqueous micellar solutions. The application to water analysis was studied.     

Spectroscopic properties of polycyclic aromatic compounds Part 6. The nitromethane selective quenching rule visited in aqueous micellar zwitterionic surfactant solvent media

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 58 representative PAH solutes dissolved in micellar N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and in micellar N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate solvent media. Results of measurements show that zwitterionic surfactants can be considered, for the most part, as providing a polar solubilizing media as far as the nitromethane selective quenching rule is concerned. Nonalternant PAHs that contain electron donating methoxy- and hydroxy-functional groups (and methyl-groups to a much lesser extent) are noted exceptions.     

Characterization of polycyclic aromatic hydrocarbons and hydroaromatics in a distillable coal-derived solvent by chromatographic and corrected fluorescence methods

Polycyclic aromatic hydrocarbons and hydroaromatics were separated from a coal-derived distillate by dry-column chromatography and high-performance liquid chromatography. Individual components in the isolated fractions were characterized by corrected excitation fluorescence spectrometry. With the chromatographic data and the fluorescence data, compound identification was possible in some cases.     

Ultrasound-assisted pressurized solvent extraction for aliphatic and polycyclic aromatic hydrocarbons from soils

In the present work the efficiency of extraction of aliphatic diesel range organics (DROs) and polycyclic aromatic hydrocarbons (PAHs) from soil was assessed by using dynamic modes of pressurized solvent extraction (PSE), and ultrasound-assisted pressurized solvent extraction (US-PSE). Optimization studies were carried out using a blank soil (Non-Polluted Soil#1, CLN-1, RTC) and a real soil which was previously spiked with the analyte mixture and aged for 90 days. A laboratory-made manifold with controlled temperature and pressure was used to carry out the leaching processes. The extraction cell was inserted into an oven for PSE and into an ultrasound bath for US-PSE. The following variables were studied in each case, keeping the pressure at about 1800 psi: extraction temperature, time of static and dynamic extraction and solvent flow rate. In addition, the time of ultrasound application was also studied in US-PSE. For PSE with dichloromethane (DCM) the recoveries were about 90-95% for both the families of analytes, using extraction times of 20 min. Analyte extraction was quantitative by using US-PSE with DCM for 10 min. In all cases, after the extraction process, the analytes were determined by GC-MS. Application of the method to a natural contaminated sample suggests that either the extraction time used in US-PSE should be increased to 20 min or the solvent (DCM) should be replaced by a mixture of DCM:acetone (1:1), to reach comparability with Soxhlet extraction.     

Quantitative analysis for polycyclic aromatic hydrocarbons by spectral decomposition of molecular fluorescence

Analysis of the molecular fluorescence spectra of several polycyclic aromatic hydrocarbons (PAH) by the technique of spectral decomposition is discussed. Peak characterization parameters obtained by this technique are utilized to obtain quantitative measurement of a mixture containing benzidiae and dibenzochrysene in solution. Application of the technique to a large number of reference compounds is discussed as an aid to routine identification of suspected carcinogens and other compounds containing fluorophores.     

Combination of micellar extraction of polycyclic aromatic hydrocarbons from aqueous media with detection by synchronous fluorescence

Summary The application of different non-ionic surfactants for the micellar extraction and enrichment of PAHs from aqueous media was tested. Recoveries were up to 100%. A spectroscopic method for the simultaneous detection of PAH-mixtures by synchronous fluorescence in the micellar phase was developed, with detection limits of 6.8 and 2.6 ng/l for benzo(k)fluoranthene and benzo(a)pyrene, respectively. The method was applied to the extraction and detection of benzo(k)fluoranthene/benzo(a)pyrene mixtures from aqueous solutions and soil suspensions. Genapol X-80 was found to suppress PAH-adsorption on bentonite at surfactant concentrations above 0.1%.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthday.     

Selective fluorescence quenching of polycyclic aromatic hydrocarbons by nitromethane within room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Recently discovered room temperature ionic liquids (RTILs) show tremendous promise to replace volatile organic compounds (VOCs). Investigation of these RTILs as solvents is in the very early stages. Before the full potential of these RTILs is realized, much more information about them as solvent systems must be obtained. The applicability of one such RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF₆), as a solvent toward analysis for polycyclic aromatic hydrocarbons (PAHs) is explored. The steady-state emission behavior of six PAHs along with the fluorescence quenching by nitromethane within BMIM PF₆ is investigated. The steady-state emission of six PAHs showed a bathochromic shift in BMIM PF₆ compared to acetonitrile, indicating possibly a more dipolar environment. Further, the nitromethane quenching of PAH emission strongly suggests a selective nature as the emission from alternant PAHs are quenched while that from nonalternant PAHs is not. The PAH-nitromethane quenching behavior within BMIM PF₆ is compared with that observed in the polar aprotic solvent acetonitrile, and a polar and similar viscosity (to BMIM PF₆) solvent system, 90 wt.% glycerol in water. It is observed that the PAH-nitromethane quenching within BMIM PF₆ and 90 wt.% glycerol in water is less efficient than in acetonitrile. This observation is suggested to arise from solvent viscosity.     

Screening method for polycyclic aromatic hydrocarbons in soil using hollow fiber membrane solvent microextraction

A fast, inexpensive screening method for polycyclic aromatic hydrocarbons in soil has been developed. Using hollow fiber membrane solvent microextraction, 8 microl of octane extraction solvent was placed inside a porous, polypropylene fiber. Following an 8 min analyte preconcentration step, 4 microl of extract was injected into a gas chromatograph. Separation was achieved in less than 10 min with a detection limit of 0.13 mg/kg for 2-methylnaphthalene. Results of both spiked and real soil samples are presented.     

Acridine dyes in the triplet state as reagents for the selective luminescence determination of polycyclic aromatic hydrocarbons

The possibility of the selective determination of several polycyclic aromatic hydrocarbons (PAH) by sensitized room-temperature phosphorescence (SRTP) in sodium dodecylsulfate (SDS) micelles was studied. Acridine dyes (trypaflavine, acridine yellow, and acridine orange) were used as triplet-energy donors. It was found that the presence of external heavy atoms of thallium(I) is a prerequisite to SRTP in the system of an acridine dye (donor) and a PAH (acceptor). The linear concentration ranges, detection limits, and selectivity factors for the determination of pyrene, anthracene, and 1,2-benzanthracene by fluorimetry, room-temperature phosphorescence (RTP), and proposed SRTP were compared.     

Spectroscopic investigations in molecularly organized solvent media. Part 5. Fluorescence behavior of polycyclic aromatic hydrocarbons dissolved in cetylpyridinium chloride+zwitterionic and cetyltrimethylammonium chloride+zwitterionic mixed surfactant systems

Applicability of the cetylpyridinium (CPy(+)) cation as a selective fluorescence quenching agent for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 25 representative solutes dissolved in two aqueous micellar cetylpyridinium chloride (CPC)+zwitterionic surfactant solvent media. Experimental results show that the CPy(+) cation effectively quenched fluorescence emission of all 10 alternant PAHs studied despite the presence of strong intramicellar coulombic interactions. Emission intensities of the 15 nonalternant PAHs also decreased upon addition of CPC to the zwitterionic surfactant solutions. Reduction in emission intensities for the nonalternant PAHs is rationalized in terms of changes in micellar structure caused by the coulombic interactions, rather than from loss of quenching selectivity by the CPy(+) cation.     

New procedure for selective extraction of polycyclic aromatic hydrocarbons in plants for gas chromatographic-mass spectrometric analysis

A new solid-phase extraction method for the clean-up and the quantitation by GC-MS of regulated polycyclic aromatic hydrocarbons (PAHs) from lettuce was developed and the experimental conditions were optimized. After ultrasonic extraction using toluene and saponification of samples, a clean-up of extracts through solid-phase extraction was performed. Samples were finally analyzed by gas chromatography-mass spectrometry (GC-MS) using an internal deuterated standard. Saponification by KOH in methanol-water (80:20) was successful allowing a good elimination of the interfering chlorophylls from the extracts containing the PAHs. The average recovery of the 16 regulated PAHs was 70, 74, 79 and 89%, respectively, for naphthalene, acenaphthylene, acenaphthene and chrysene and higher than 94% for the others.     

超高效液相色谱荧光检测器测定土壤中多环芳烃

建立了超高效液相色谱系统(UPLC)荧光检测土壤中15种美国环境保护署(USEPA)优控的多环芳烃(PAHs),简化了土壤样品中PAHs的前处理过程。UPLC对15种PAHs分离时间为17 min,流速为0.4 mL/min。荧光检测器对15种PAHs的检出限为0.03~1.53μg/L,6次重复测定的峰面积相对标准偏差为0.12%~0.99%。除了萘和苊外,土样加标的平均回收率为82.9%~103.4%。由于色谱柱的较高分辨率以及荧光检测器的较高选择性,在定性和定量研究土壤样品中的PAHs时,提取物的硅胶柱净化步骤可以省略。