Laser-excited Time-resolved Shpol Research Articles

Chromatographic and spectroscopic analysis of Dibenzo[b,l]Fluoranthene and its determination in SRM 1597a by laser-excited time-resolved Shpol'skii spectroscopy

BackgroundPolycyclic aromatic hydrocarbons (PAHs) with molecular mass 302 Da are the most investigated PAHs within the high molecular weight PAHs class. This PAH class contributes to a significant portion of the mutagenic and/or carcinogenic response associated to the PAH fraction present in environmental and combustion-related samples. Several reasons prevent the routine analysis of 302 Da PAHs in environmental samples, including large number of possible isomers, limited number of commercially available reference standards, and low concentration levels. ResultsThese studies search for a newly synthetized dibenzo-fluoranthene of molecular mass 302 Da, namely dibenzo[b,l]fluoranthene, in a standard reference material (SRM 1597a) from the National Institute of Standards and Technology. The eluting behavior of dibenzo[b,l]fluoranthene is investigated under reversed-phase liquid chromatographic conditions for its determination via absorption and fluorescence detection. Vibrationally resolved spectra and fluorescence lifetimes recorded from octane matrices at 77 K and 4.2 K allow for its qualitative and quantitative analysis at the parts-per-trillion concentration levels. Its unambiguous determination is then reported for the first time in the SRM 1597a. Significance and noveltyOf the 89 possible 302 Da PAH isomers, only 23 isomers have been identified in SRMs and/or environmental samples. The determination of dibenzo[b,l]fluoranthene in the SRM 1597a takes a step forward to fulfilling this gap.

Instrumental improvements for the trace analysis of structural isomers of polycyclic aromatic hydrocarbons with molecular mass 302 Da

Polycyclic aromatic hydrocarbons (PAHs) are some of the most common environmental pollutants encountered worldwide. Eco-toxicological studies attribute a significant portion of the biological activity of PAH contaminated samples to the presence of high molecular weight PAHs (HMW-PAHs), i.e. PAHs with molecular mass (MM) greater than 300 Da. The research presented here focuses on the analysis of PAH isomers of MM 302 Da. This is not a trivial task. There are 23 isomers with MM 302 Da available to commercial and academic researchers. Many of them are difficult to separate in the chromatographic column and have virtually identical fragmentation patterns. The selectivity of HPLC absorption and fluorescence detectors is modest for resolving co-eluting isomers. Previous work in our lab demonstrated the potential of laser excited time-resolved Shpol’skii spectroscopy (LETRSS) for the analysis of 302 Da isomers in HPLC fractions. The main limitation of the technique was instrumental and due to the narrow range of excitation wavelengths of the tunable dye laser used for sample excitation. Herein, we remove this limitation with an optical parametric oscillator (OPO)-based wavelength tuning laser that covers the whole excitation range of 302 Da isomers. It is possible now to excite each isomer at its excitation wavelength for maximum fluorescence emission and reach limits of detection at the parts-per-trillion level (pg.mL−1). The excitation bandwidth of the OPO laser (0.2 nm) is a good match for the narrow excitation spectra of 302 Da isomers in n-octane. This feature, associated to unique vibrational fluorescence profiles and lifetime decays, allows for the unambiguous identification of co-eluting isomers in RPLC fractions. The same is true for their quantitative analysis in coal tar samples.

Determination of high-molecular weight polycyclic aromatic hydrocarbons in high performance liquid chromatography fractions of coal tar standard reference material 1597a via solid-phase nanoextraction and laser-excited time-resolved Shpol'skii spectroscopy

This article presents an alternative approach for the analysis of high molecular weight – polycyclic aromatic hydrocarbons (HMW-PAHs) with molecular mass 302Da in complex environmental samples. This is not a trivial task due to the large number of molecular mass 302Da isomers with very similar chromatographic elution times and similar, possibly even virtually identical, mass fragmentation patterns. The method presented here is based on 4.2K laser-excited time-resolved Shpol'skii spectroscopy, a high resolution spectroscopic technique with the appropriate selectivity for the unambiguous determination of PAHs with the same molecular mass. The potential of this approach is demonstrated here with the analysis of a coal tar standard reference material (SRM) 1597a. Liquid chromatography fractions were submitted to the spectroscopic analysis of five targeted isomers, namely dibenzo[a,l]pyrene, dibenzo[a,e]pyrene, dibenzo[a,i]pyrene, naphtho[2,3-a]pyrene and dibenzo[a,h]pyrene. Prior to analyte determination, the liquid chromatographic fractions were pre-concentrated with gold nanoparticles. Complete analysis was possible with microliters of chromatographic fractions and organic solvents. The limits of detection varied from 0.05 (dibenzo[a,l]pyrene) to 0.24µgL−1 (dibenzo[a,e]pyrene). The excellent analytical figures of merit associated to its non-destructive nature, which provides ample opportunity for further analysis with other instrumental methods, makes this approach an attractive alternative for the determination of PAH isomers in complex environmental samples.

Pre-concentration of water samples with BEA zeolite for the direct determination of polycyclic aromatic hydrocarbons with laser-excited time-resolved Shpol'skii spectroscopy

A unique method for screening fifteen US Environmental Protection Agency polycyclic aromatic hydrocarbons (EPA-PAHs) in drinking and lake water samples is reported. One milliliter volume of water sample is mixed and centrifuged with 2 mg of BEA zeolite. The precipitate is subsequently treated with equal volumes (100 μL) of a 70/30 methanol–water mixture and n-octane. Fifteen EPA-PAHs are directly determined (no chromatographic separation) in the layer of n-octane via 4.2 K laser-excited time-resolved Shpol'skii spectroscopy. A mathematical equation is derived to correlate the PAH concentration in the water sample to its concentration in the layer of Shpol'skii solvent (n-octane). Qualitative and quantitative analyses are based on the collection of wavelength–time matrices, i.e. data formats that carry with them spectral and lifetime information. With 1 mL of water, the limits of detection varied from 1.1 ng L − 1 (benzo[ a ]pyrene) to 194 ng L − 1 (naphthalene). The analytical recoveries of the new method are in good agreement with those obtained via high-performance liquid chromatography. The simplicity of the experimental procedure and the use of microliters of organic solvent make the new method a valuable and environmentally friendly alternative for the routine monitoring of EPA-PAHs in water samples. • Green methodology is presented for monitoring of polycyclic aromatic hydrocarbons. • Complete analysis is possible with 1 mL of water. • Sample analysis consumes 2 mg of zeolite and 170 μL of solvent. • Limits of detection are at the ng L − 1 to pg L − 1 concentration level.

Four-way modeling of 4.2 K time-resolved excitation emission fluorescence data for the quantitation of polycyclic aromatic hydrocarbons in soil samples

A screening method for the soil analysis of 15 Environmental Protection Agency-polycyclic aromatic hydrocarbons (EPA-PAHs) is reported. The new method is based on the collection of 4.2K fluorescence time-resolved excitation–emission cubes (TREECs) via laser-excited time-resolved Shpol'skii spectroscopy. 4.2K fluorescence TREECs result from the superposition of fluorescence time-resolved excitation emission matrices recorded at different time windows from the laser excitation pulse. Potential interference from unknown sample concomitants is handled by processing the four-way 4.2K fluorescence TREEC data arrays with either parallel factor analysis (PARAFAC) or unfolded partial least-squares/residual-trilinearization(U-PLS/RTL). The sensitivity of the two approaches makes possible to determine PAHs at the ngg−1 to pgg−1 concentration level with no need for sample pre-concentration. Its selectivity eliminates sample clean-up steps and chromatographic separation. These features reduce PAH loss, analysis time and cost. The method is environmentally friendly as the complete screening of the 15 EPA-PAHs takes only 250μL of organic solvent per sample.

Analysis of co-eluted isomers of high-molecular weight polycyclic aromatic hydrocarbons in high performance liquid chromatography fractions via solid-phase nanoextraction and time-resolved Shpol'skii spectroscopy

We present an accurate method for the determination of isomers of high-molecular weight polycyclic aromatic hydrocarbons co-eluted in HPLC fractions. The feasibility of this approach is demonstrated with two isomers of molecular weight 302 with identical mass fragmentation patterns, namely dibenzo[ a,i]pyrene and naphtho[2,3- a]pyrene. Qualitative and quantitative analysis is carried out via laser-excited time-resolved Shpol'skii spectroscopy at liquid helium temperature. Unambiguous identification of co-eluted isomers is based on their characteristic 4.2 K line-narrowed spectra in n-octane as well as their fluorescence lifetimes. Pre-concentration of HPLC fractions prior to spectroscopic analysis is performed with the aid of gold nanoparticles via an environmentally friendly procedure. In addition to the two co-eluted isomers, the analytical figures of merit of the entire procedure were evaluated with dibenzo[ a,l]pyrene, dibenzo[ a,h]pyrene and dibenzo[ a,e]pyrene. The analytical recoveries from drinking water samples varied between 98.2 ± 5.5 (dibenzo[ a,l]pyrene) and 102.7 ± 3.2% (dibenzo[ a,i]pyrene). The limits of detection ranged from 51.1 ng L −1 (naphtho[2,3- a]pyrene) to 154 ng L −1 (dibenzo[ a,e]pyrene). The excellent analytical figures of merit associated to its HPLC compatibility makes this approach an attractive alternative for the analysis of co-eluted isomers with identical mass spectra.

Determination of polycyclic aromatic hydrocarbons with molecular weight 302 in water samples by solid-phase nano-extraction and laser excited time-resolved shpol'skii spectroscopy

Monitoring of high-molecular weight polycyclic aromatic hydrocarbons (HMW-PAH) via simple and cost effective methods still remains a challenge. In this article, we combine solid-phase nano-extraction (SPNE) and 4.2 K laser-excited time resolved Shpol'skii spectroscopy (LETRSS) into a valuable alternative for the water analysis of dibenzo[a,l]pyrene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene and naphtho[2,3-a]pyrene. In comparison to the original SPNE procedure, the present method improves PAH recoveries and reduces extraction time from 30 to 20 min per sample. Quantitative release of HMW-PAH into the Shpol'skii matrix (n-octane) is best accomplished with a mixture of 48 μL of methanol and 2 μL of 1-pentanethiol. Their migration into the 50 μL layer of n-octane provides highly resolved spectra with distinct fluorescence lifetimes for unambiguous isomer determination. Complete analysis takes less than 30 min per sample and consumes only 100 micro-liters of organic solvents. 500 μL of water are sufficient to obtain limits of detection ranging from 16 ng L(-1) (dibenzo[a,l]pyrene) to 55 ng L(-1) (dibenzo[a,i]pyrene), relative standard deviations better than 3% and analytical recoveries above 90%. Although a straightforward comparison to chromatographic methods is not possible because of the lack of analytical figures of merit on HMW-PAH, the excellent precision of measurements, limits of detection and overall recoveries makes SPNE-LETRSS an attractive approach to water analysis of HMW-PAH.

Direct determination of benzo[ a]pyrene in water samples by a gold nanoparticle-based solid phase extraction method and laser-excited time-resolved Shpol'skii spectrometry

The strong affinity between polycyclic aromatic hydrocarbons (PAH) and the surface of gold colloids is investigated to device an extraction method for water samples. Within the 20–100 nm particle diameter range, the 20 nm gold nanoparticles showed the best extraction efficiencies for all the studied analytes. The new approach is combined to laser-excited time-resolved Shpol'skii spectrometry for the direct analysis of benzo[ a]pyrene in drinking water samples. For a 500 μL sample volume, the analytical figures of merit demonstrate precise and accurate analysis at the parts-per-trillion level. The extraction efficiencies are statistically equivalent to 100% with relative standard deviations lower than 2%. The average recoveries were varied from 87.5% to 96.5% for different concentration of analytes. The simplicity of the experimental procedure, the low analysis cost, and the excellent analytical figures of merit demonstrate the potential of this approach for routine analysis of drinking water samples.

Solid-phase nano-extraction and laser-excited time-resolved Shpol’skii spectroscopy for the analysis of polycyclic aromatic hydrocarbons in drinking water samples

A unique method for screening polycyclic aromatic hydrocarbons in drinking water samples is reported. Water samples (500 μl) are mixed and centrifuged with 950 μl of a commercial solution of 20 nm gold nanoparticles for pollutants extraction. The precipitate is treated with 2 μl of 1-pentanethiol and 48 μl of n-octane, and the supernatant is then analyzed via laser-excited time-resolved Shpol’skii spectroscopy. Fifteen priority pollutants are directly determined at liquid helium temperature (4.2 K) with the aid of a cryogenic fiber-optic probe. Unambiguous pollutant determination is carried out via spectral and lifetime analysis. Limits of detection are at the parts-per-trillion level. Analytical recoveries are similar to those obtained via high-performance liquid chromatography. The simplicity of the experimental procedure, use of microliters of organic solvent, short analysis time, selectivity, and excellent analytical figures of merit demonstrate the advantages of this environmentally friendly approach for routine analysis of numerous samples.

Four-Way Data Coupled to Parallel Factor Model Applied to Environmental Analysis: Determination of 2,3,7,8-Tetrachloro-dibenzo-para-dioxin in Highly Contaminated Waters by Solid−Liquid Extraction Laser-Excited Time-Resolved Shpol'skii Spectroscopy

This article reports the first application of parallel factor analysis to high-order instrumental data generated from Shpol'skii matrixes at liquid helium temperature. Third-order data arrays-consisting of excitation modulated wavelength time matrixes-are collected with the aid of a cryogenic fiber-optic probe, a tunable dye laser, and a multichannel system for phosphorescence detection. The multidimensional data formats are applied to the analysis of 2,3,7,8-tetrachloro-dibenzo-para-dioxin in water samples. The experimental procedure is rapid and environmentally friendly. Complete sample analysis is accomplished in less than 15 min with only 100 muL of organic solvent (n-heptane). The feasibility to directly determine parts-per-trillion concentration levels of the target compound is demonstrated with heavily contaminated samples of unknown composition. The limits of detection, estimated from calibrations based on the univariate method and parallel factor analysis, are 0.060 and 0.092 ng.mL(-1), respectively; both referred to a 100 mL water sample.

Direct Determination of Dibenzo[a,l]pyrene and Its Four Dibenzopyrene Isomers in Water Samples by Solid−Liquid Extraction and Laser-Excited Time-Resolved Shpol'skii Spectrometry

Dibenzo[a,l]pyrene is considered the most potent carcinogen of all polycyclic aromatic hydrocarbons ever tested. Its four isomers, which include dibenzo[a,e]pyrene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, and dibenzo[e,l]pyrene, are also carcinogenic and, therefore, a potential threat to humans. The method presented here provides a direct way for their determination in water samples. The entire procedure--from water extraction to LETRSS analysis--takes less than 15 min/sample and it consumes only 100 microL of organic solvent. This fact makes our approach environmentally friendly and cost-effective. Unambiguous isomer determination is accomplished via multidimensional data formats, namely, wavelength time matrixes, excitation-emission matrixes, and time-resolved excitation-emission matrixes. The analytical figures of merit demonstrate precise and accurate analysis at the sub-parts-per-billion level. Limits of detection are at the parts-per-trillion level. The potential of this approach for real-world analysis is illustrated with a heavily contaminated water samples.

Laser-Excited Time-Resolved Shpol'skii Spectroscopy for the Direct Analysis of Dibenzopyrene Isomers in Liquid Chromatography Fractions

We present a unique method for the unambiguous determination of dibenzo[a,l]pyrene, dibenzo[a,e]pyrene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, and dibenzo[e,l]pyrene in high-performance liquid chromatography (HPLC) fractions. Chemical analysis is performed via laser-excited time-resolved Shpol'skii spectroscopy with the aid of a cryogenic fiber-optic probe, pulsed tunable dye laser, spectrograph, and intensified charge-coupled device. Unambiguous identification is accomplished via wavelength time matrix formats, which give simultaneous access to spectral and lifetime information. Prior to spectroscopic analysis, HPLC fractions are pre-treated with liquid-liquid extraction or solid-liquid extraction at the tip of the fiber-optic probe. Solid-liquid extraction gives the best limits of detection, which vary from 40 pg mL(-1) (dibenzo[a,l]pyrene) to 0.2 ng mL(-1)(dibenzo[e,l]pyrene).

Analysis of polycyclic aromatic hydrocarbons in HPLC fractions by laser-excited time-resolved Shpol'skii spectrometry with cryogenic fiber-optic probes

Laser-excited time-resolved Shpol'skii spectrometry at liquid helium temperature (4.2 K) is presented for the analysis of polycyclic aromatic hydrocarbons in high-performance liquid chromatography fractions. Fluorescence measurements are rapidly done with the aid of a fiber-optic probe, pulsed tunable dye laser, spectrograph, and intensified charge-coupled device. Analyte identification and peak-purity checking are made through wavelength–time matrix formats, which give simultaneous access to spectral and lifetime information. Sample preparation is rapid and simple. It involves liquid–liquid extraction or solid–liquid extraction of chromatographic fractions at the tip of the fiber-optic probe. The potential of both approaches is demonstrated with the semi-quantitative analysis of priority pollutants in heavily contaminated water samples.

A novel approach for solid–liquid extraction laser-excited time-resolved Shpol'skii spectrometry

A new procedure is presented for the analysis of polycyclic aromatic hydrocarbons by solid–liquid extraction (SLE) and laser-excited time-resolved Shpol'skii spectrometry (LETRSS). Microliters of Shpol'skii solvent are spiked on the surface of the extraction membrane and LETRSS is directly performed on the organic layer above the surface of the solid substrate. Fluorescence measurements are easily performed with a fiber-optic cell specifically designed for cryogenic measurements at 77 and 4.2 K. In comparison to the SLE–LETRSS procedure previously reported (Environ. Sci. Technol. 35 (2001) 2566), the spiking procedure eliminates the eluting step, reduces solvent consumption and improves limits of detection for at least one order of magnitude.