Differentiating Nylon Samples with Visually Indistinguishable Fluorescence Using Principal Component Analysis and Common Dimension Partial Least Squares Linear Discriminant Analysis with Synchronous Fluorescence Spectroscopy.

Fluorescence spectroscopy is an attractive candidate for analyzing samples of nylon. Impurities within the polymers formed during the synthesis and processing of nylons give rise to the observed fluorescence, allowing for nylons to be analyzed based on their impurities. Nylons from the same source are expected to display similar fluorescence profiles, and nylons with different fluorescence are expected to be from different sources. This paper investigates an important case where different nylons displayed similar fluorescence, preventing easy discrimination. Samples of Nylon 6 and Nylon 6/12 had visually indistinguishable excitation-emission matrices (EEM), excitation spectra, fluorescence spectra, and synchronous fluorescence spectra at larger Δλ. By collecting synchronous fluorescence spectra at smaller Δλ, additional features in the fluorescence profiles were identified that allowed for some discrimination between the two nylons. Combining the EEM and synchronous fluorescence data with chemometric algorithms provided a clearer differentiation between the two nylons. parallel factor analysis, principal component analysis, and common dimension partial least squares (ComDim-PLS) showed two distinct clusters in the data, with ComDim-PLS providing the greatest distinction between the clusters. The loadings revealed the variables of interest to the ComDim-PLS were the 400 nm and 335 nm bands for all synchronous fluorescence spectra, the 460 nm and 310 nm bands for the Δλ = 20 nm and Δλ = 30 nm synchronous fluorescence spectra, and the 440 nm band for the Δλ = 20 nm synchronous fluorescence spectra. The linear discriminant analysis performed with the PLS data yielded a classification accuracy of 95% with the EEM data and 100% with the synchronous fluorescence data, displaying the power of this technique to differentiate two different nylons with visually indistinguishable fluorescence spectra.

Sorption of Polycyclic Aromatic Sulfur Heterocycles (PASH) on Nylon Microplastics at Environmentally Relevant Concentrations.

Microplastics have garnered an infamous reputation as a sorbate for many concerning environmental pollutants and as a delivery vehicle for the aquatic food chain through the ingestion of these contaminated small particulates. While sorption mechanisms have been extensively studied for polycyclic aromatic hydrocarbons, polycyclic aromatic sulfur heterocycles (PASHs) have not been investigated, partly due to their low concentrations in aquatic ecosystems. Herein, an analytical methodology is presented for the analysis of dibenzothiophene, benzo[b]naphtho[1,2-b]thiophene, benzo[b]naphtho[2,1-b]thiophene, benzo[b]naphtho[2,3-b]thiophene, chryseno[4,5-bcd]thiophene and dinaphtho[1,2-b:1',2'-d]thiophene at relevant environmental concentrations based on solid phase extraction and high-performance liquid chromatography. The sorption uptake behavior and the sorption kinetics of the three benzo[b]napthothiophene isomers were then investigated on nylon microplastics to provide original information on their environmental fate and avoid human contamination through the food chain. The obtained information might also prove relevant to the development of successful remediation approaches for aquatic ecosystems.

Screening method for the analysis of Rhodamine B in chili powder.

Rhodamine B is a synthetic dye known to enhance the visual appearance of chili powder. Due to its toxicity and carcinogenicity, chromatographic methods have been developed to monitor its presence in adulterated chili powder, but their assays are laborious, time consuming and expensive for screening purposes. The present studies propose an alternative for screening Rhodamine B in chili powder samples. The method combines thin layer chromatography (TLC) to solid surface room-temperature fluorescence spectroscopy. The scrape-dissolution procedure common to the instrumental analysis of TLC procedures was replaced with a fiber optic probe coupled to a commercial spectrofluorometer. The determination of Rhodamine B on the chromatographic plate is based on its retardation factor and maximum excitation and emission wavelengths. The limit of detection (1.9 ng.mL-1) and the limit of quantitation (5.2 ng.mL-1) are well below the usual contamination of Rhodamine B in adulterated foods.

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

BACKGROUND: Polycyclic 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. RESULTS: These 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 NOVELTY: Of 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.

Investigation of the Effects of Dioctyl Sulfosuccinate on the Photodegradation of Benzo[a]Pyrene in Aqueous Solutions under Various Wavelength Regimes.

Due to the relatively high concentrations of polycyclic aromatic hydrocarbons (PAHs) in oil samples, oil spills in aquatic ecosystems release significant amounts of PAHs. Although remediation efforts often take place during or immediately after an oil spill incident, a portion of the released PAHs remains in the body of water. A natural phenomenon resulting from the direct exposure of PAHs to sunlight is photodegradation. This article investigates the effect of dioctyl sulfosuccinate (DOSS) on the photodegradation of benzo[a]pyrene (BaP), the most toxic PAH in the priority pollutants list of the US Environmental Protection Agency (EPA). DOSS is a surfactant typically used in the remediation of oil spills. Three lamps with maximum emission wavelengths at 350 nm, 419 nm, and 575 nm were individually and simultaneously used to irradiate aqueous solutions of BaP in the absence and the presence of DOSS. When irradiated with the 419 nm lamp or the 575 lamp, BaP showed no photodegradation. Upon irradiation with the 350 nm lamp and with the simultaneous use of the three lamps, the photodegradation of BaP followed first-order kinetics. Independent of the irradiation wavelength, the presence of DOSS increased the half-life of BaP in the aqueous solution. In the case of the 350 nm lamp, the rate constant of photodegradation in the absence and the presence of DOSS varied from (3.79 ± 0.97) × 10-3 min-1 to (1.10 ± 0.13) × 10-3 min-1, respectively. Under simultaneous irradiation with the lamps, the rate constant of photodegradation varied from (1.12 ± 0.35) × 10-3 min (no DOSS) to (3.30 ± 0.87) × 10-4 (with DOSS). Since the largest rate constants of photodegradation were observed in the absence of DOSS, the longer half-lives of BaP in the presence of surfactant were attributed to the incorporation of PAH molecules into the DOSS micelles.

Biomonitoring of polycyclic aromatic hydrocarbons in Brazilian pregnant women: Urinary levels and health risk assessment.

Over the years, humans have been continuously exposed to several compounds directly generated by industrial processes and/or present in consumed products. Polycyclic aromatic hydrocarbons (PAHs) are legacy pollutants ubiquitous in the environment and represent the main chemical pollutants in urban areas. Worldwide, studies that aim to understand the impacts of exposure to these chemicals have gained increasing prominence due to their potential toxicity profile, mainly concerning genotoxicity and carcinogenicity. Human biomonitoring (HB) is an analytical approach to monitoring population exposure to chemicals; however, these studies are still limited in Brazil. Thus, this work aimed to evaluate the exposure of Brazilian pregnant women to PAHs through HB studies. Besides, the risk characterization of this exposure was performed. For this purpose, urine samples from 358 Brazilian pregnant women were used to evaluate 11 hydroxylated metabolites of PAHs employing gas chromatography coupled to mass spectrometry. The 1OH-naphthol and 2OH-naphthol were detected in 100% of the samples and showed high levels, corresponding to 16.99 and 3.62 µg/g of creatinine, respectively. 2OH-fluorene (8.12 µg/g of creatinine) and 9OH-fluorene (1.26 µg/g of creatinine) were detected in 91% and 66% of the samples, respectively. Benzo(a)pyrene (BaP) metabolites were detected in more than 50% of the samples (0.58-1.26 µg/g of creatinine). A hazard index of 1.4 and a carcinogenic risk above 10-4 were found for BaP metabolites in the risk characterization. Therefore, our findings may indicate that exposure to PAHs poses a potential risk to pregnant women's health and a high probability of carcinogenic risk due to their exposure to BaP. Finally, this work shows the need for more in-depth studies to determine the sources of exposure and the implementation of health protection measures regarding the exposure of the Brazilian population to PAHs.

Risk characterization of human exposure to polycyclic aromatic hydrocarbons in vulnerable groups.

Nowadays, anthropogenic activities are a significant source of environmental pollutants at an alarming rate. Polycyclic aromatic hydrocarbons (PAHs) are widely spread and well-known mutagenic and carcinogenic legacy pollutants of public health concern. In underdeveloped countries like Brazil, limited data are available in the scientific literature on the risk assessment of exposure to PAHs, leading to a risk underestimation, especially in the vulnerable groups of the population. In the current investigation, we have measured seven PAH metabolites in healthy vulnerable groups (n = 400), including pregnant and lactating women, newborns, and children. Besides, according to the United States Environmental Protection Agency (US.EPA) guidelines, the risk characterization of this exposure was performed by calculating estimated daily intake, hazard quotient, hazard index, and cancer risk. The highest levels and detection rates for all metabolites were found in pregnant women, with 15.71 ng/mL for the ∑OH-PAHs, presumably due to the increased metabolic rate related to pregnancy. The lowest ∑OH-PAHs were detected in infants, with 2.33 ng/mL due to unmatured metabolism. When analyzing the health hazards, the non-carcinogenic risk - as a sum of all PAH metabolites, we observed a health risk (in all groups) above the limit that the US.EPA considers without significant potential health risk. Regarding cancer risks, benzo[a]pyrene levels in all the groups indicated a potential risk. In general, higher levels of potential cancer risk were observed for lactating women, which implies risks to them and their infants. Low molecular weight PAHs (naphthalene, fluorene, and phenanthrene) are associated with acute toxic effects. Their high detection rate (i.e., naphthalene: 100 %) demonstrates their extensive exposure, making these PAHs a priority for human biomonitoring. Besides, benzo[a]pyrene is carcinogenic to humans, being also important to monitor its levels since our risk assessment showed a high cancer risk to this PAH.

The influence of the co-exposure to polycyclic aromatic hydrocarbons and toxic metals on DNA damage in brazilian lactating women and their infants: A cross-sectional study using machine learning approaches.

Polycyclic aromatic hydrocarbons (PAHs) and toxic metals are widely spread pollutants of public health concern. The co-contamination of these chemicals in the environment is frequent, but relatively little is known about their combined toxicities. In this context, this study aimed to evaluate the influence of the co-exposure to PAHs and toxic metals on DNA damage in Brazilian lactating women and their infants using machine learning approaches. Data were collected from an observational, cross-sectional study with 96 lactating women and 96 infants living in two cities. The exposure to these pollutants was estimated by determining urinary levels of seven mono-hydroxylated PAH metabolites and the free form of three toxic metals. 8-Hydroxydeoxyguanosine (8-OHdG) levels in the urine were used as the oxidative stress biomarker and set as the outcome. Individual sociodemographic factors were also collected using questionnaires. Sixteen machine learning algorithms were trained using 10-fold cross-validation to investigate the associations of urinary OH-PAHs and metals with 8-OHdG levels. This approach was also compared with models attained by multiple linear regression. The results showed that the urinary concentration of OH-PAHs was highly correlated between the mothers and their infants. Multiple linear regression did not show a statistically significant association between the contaminants and urinary 8OHdG levels. Machine learning models indicated that all investigated variables did not present predictive performance on 8-OHdG concentrations. In conclusion, PAHs and toxic metals were not associated with 8-OHdG levels in Brazilian lactating women and their infants. These novelty and originality results were achieved even after applying sophisticated statistical models to capture non-linear relationships. However, these findings should be interpreted cautiously because the exposure to the studied contaminants was considerably low, which may not reflect other populations at risk.

On the co-elution of benzo[a]pyrene and dibenzo[a,l]pyrene in chromatographic fractions and their unambiguous determination in tobacco extracts via laser-excited time resolved Shpol'skii spectroscopy.

High performance liquid chromatography is widely used for the analysis of polycyclic aromatic hydrocarbons in a wide variety of samples. Of particular concern are benzo[a]pyrene and dibenzo[a,l]pyrene, two of the most toxic polycyclic aromatic hydrocarbons ever tested. Under EPA method 610, these two compounds co-elute with almost identical retention times. Our studies demonstrate the feasibility of directly determining them in a chromatographic fraction without further separation. Their unambiguous determination is based on spectral and lifetime information with a two-step experimental procedure consisting of the evaporation of the chromatographic fraction followed by the dissolution of the residue with microliters of n-octane. With the aid of a 77 K fiber optic probe, limits of detection at the parts-per-billion concentration level (ng mL-1) are obtained from the microliter sample via laser excited time resolved Shpol'skii spectroscopy. This approach is then applied to the analysis of benzo[a]pyrene and dibenzo[a,l]pyrene in tobacco extracts.

Polycyclic aromatic hydrocarbons (PAHs): Updated aspects of their determination, kinetics in the human body, and toxicity.

Polycyclic aromatic hydrocarbons (PAHs) are legacy pollutants of considerable public health concern. Polycyclic aromatic hydrocarbons arise from natural and anthropogenic sources and are ubiquitously present in the environment. Several PAHs are highly toxic to humans with associated carcinogenic and mutagenic properties. Further, more severe harmful effects on human- and environmental health have been attributed to the presence of high molecular weight (HMW) PAHs, that is PAHs with molecular mass greater than 300 Da. However, more research has been conducted using low molecular weight (LMW) PAHs). In addition, no HMW PAHs are on the priority pollutants list of the United States Environmental Protection Agency (US EPA), which is limited to only 16 PAHs. However, limited analytical methodologies for separating and determining HMW PAHs and their potential isomers and lack of readily available commercial standards make research with these compounds challenging. Since most of the PAH kinetic data originate from animal studies, our understanding of the effects of PAHs on humans is still minimal. In addition, current knowledge of toxic effects after exposure to PAHs may be underrepresented since most investigations focused on exposure to a single PAH. Currently, information on PAH mixtures is limited. Thus, this review aims to critically assess the current knowledge of PAH chemical properties, their kinetic disposition, and toxicity to humans. Further, future research needs to improve and provide the missing information and minimize PAH exposure to humans.

Advances in Chemical Analysis of Oil Spills Since the Deepwater Horizon Disaster.

Analytical techniques for chemical analysis of oil, oil photochemical and biological transformation products, and dispersants and their biodegradation products benefited significantly from research following the 2010 Deepwater Horizon (DWH) disaster. Crude oil and weathered-oil matrix reference materials were developed based on the Macondo well oil and characterized for polycyclic aromatic hydrocarbons, hopanes, and steranes for use to assure and improve the quality of analytical measurements in oil spill research. Advanced gas chromatography (GC) techniques such as comprehensive two-dimensional GC (GC × GC), pyrolysis GC with mass spectrometry (MS), and GC with tandem MS (GC-MS/MS) provide a greater understanding at the molecular level of composition and complexity of oil and weathering changes. The capabilities of high-resolution MS (HRMS) were utilized to extend the analytical characterization window beyond conventional GC-based methods to include polar and high molecular mass components (>400 Da) and to provide new opportunities for discovery, characterization, and investigation of photooxidation and biotransformation products. Novel separation approaches to reduce the complexity of the oil and weathered oil prior to high-resolution MS and advanced fluorescence spectrometry have increased the information available on spilled oil and transformation products. HRMS methods were developed to achieve the required precision and sensitivity for detection of dispersants and to provide molecular-level characterization of the complex surfactants. Overall, research funding following the DWH oil spill significantly advanced and expanded the use of analytical techniques for chemical analysis to support petroleum and dispersant characterization and investigations of fate and effects of not only the DWH oil spill but future spills.

Nondestructive Forensic Comparison of Nylon Trace Evidence Using Room-Temperature Fluorescence Spectroscopy.

The increasing accessibility of 3D printers makes their use for criminal activity more likely. Current forensic analysis of trace evidence left by 3D-printed materials focuses on identifying the general type of plastic, which includes acrylonitrile butadiene styrene, polylactic acid, nylon, polycarbonate, polyethylene terephthalate, and chlorinated polyethylene. Herein, we present a nondestructive approach capable of differentiating among different types of nylons. The new approach is based on room-temperature fluorescence spectroscopy. Excitation-emission matrices, excitation and emission spectra, and synchronous fluorescence spectra are directly recorded from single microplastics with the aid of a fiber-optic probe coupled to a commercial spectrofluorometer. The comparison of spectral features demonstrates the capability to differentiate microparticles originating from Nylon 11, Nylon 12, Nylon 6/6, and Nylon 6/12. The observed differences are attributed to the presence of fluorescent impurities embedded in the polymer during its fabrication. The outstanding matching of excitation-emission matrices, excitation and emission spectra, and synchronous fluorescence spectra demonstrates the potential of this approach to link trace evidence to a specific source beyond its general plastic type.

Urinary levels of monohydroxylated polycyclic aromatic hydrocarbons in Brazilian children and health risk assessment: a human biomonitoring-based study.

Monitoring human exposure to polycyclic aromatic hydrocarbons (PAHs) is a public health concern. Children are a vulnerable subgroup of the population with limited human biomonitoring data worldwide. Thus, this study aimed to measure the levels of seven PAH metabolites in urine from Brazilian children and provide risk assessment values for this exposure. Our data show naphthalene was the major contributor to children's exposure to PAHs, with a 100% detection rate. Children in urban regions presented higher exposure to PAHs, with higher concentrations of 2-naphthol in the southeast (1.09 ng/mL, p < 0.05). Furthermore, the highest concentration of 2-naphthol was found in older children (p = 0.02), suggesting a possible difference in dietary habits. Exposure to the carbaryl insecticide is suggested based on the high concentrations of 1-naphthol (1.29 ng/mL) and considering the ratio 1-naphthol/2-naphthol (1.78). Moreover, the positive correlation between the metabolites of fluorine and pyrene also suggests exposure to PAHs by petrol combustion. The risk assessment of the PAH exposure was evaluated using the estimated daily intake (EDI) for two naphthalene metabolites in the study with a 100% detection rate. The EDI was 14.47 ng/kg BW/day. The risk assessment to the PAH exposure revealed a non-carcinogenic risk profile, with a hazard quotient of 0.71. To the best of our knowledge, this study is the first to provide levels of PAHs in Brazilian children.

A fast-multiclass method for the determination of 21 endocrine disruptors in human urine by using vortex-assisted dispersive liquid-liquid microextraction (VADLLME) and LC-MS/MS.

Simplicity, speed, and reduced cost are essential demands for routine analysis in human biomonitoring studies. Moreover, the availability of higher volumes of human specimens is becoming more restrictive due to ethical controls and to the costs associated with sample transportation and storage. Thus, analytical methods requiring much lower sample volumes associated with simultaneous detection capability (multiclass analysis) are with a very high claim. In this sense, the present approach aimed at the development of a method for preconcentration and simultaneous determination of four classes of endocrine disruptors (seven bisphenols, seven parabens, five benzophenones, and two antimicrobials) in the urine. The approach is based on vortex-assisted dispersive liquid-liquid microextraction (VADLLME) and high-performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). After optimization of the significant parameters of VADLLME extraction, the proposed procedure showed to be simple, fast, sensitive, requiring only 1.0 mL of urine, 400 µL of organic solvents with a total stirring time of 20 s. Moreover, a variation of inter-day and between-day runs were lower than 10.0% and 11.0%, respectively. Finally, the proposed method was successfully applied to the analysis of 50 urine samples of Brazilian pregnant women to establish reference ranges.

Shpol'skii spectroscopy of metabolites of polycyclic aromatic hydrocarbons in primary alcohols at 77 K and 4.2 K.

We present for the first time experimental evidence on the line-narrowing effect caused by primary alcohols on the spectral features of metabolites of polycyclic aromatic hydrocarbons at 77 K and 4.2 K. The investigated metabolites include 1-hydroxypyrene, 2-hydroxyfluorene, 9-hydroxyphenanthrene, 3-hydroxybenzo[a]pyrene, 4-hydroxybenzo[a]pyrene, 5-hydroxybenzo[a]pyrene, B[a]P-trans-7,8-dihydrodiol (±), B[a]P-trans-9,10-dihydrodiol (±), B[a]P-r-7,t-8-dihydrodiol-c-9,10-epoxide (±) and B[a]P-r-7,t-8-dihydrodiol-t-9,10-epoxide(±). The narrowest spectra and highest fluorescence enhancements were observed by matching the length of the alcohol to the length of the n-alkane that best fits the molecular dimensions of the parent polycyclic aromatic hydrocarbons. The analytical figures of merit show potential for the qualitative and quantitative analysis of PAH metabolites via Shpol'skii Spectroscopy.

Characterization of a Bio-sourced, Fluorescent, Ratiometric pH Indicator with Alkaline pKa.

Utilizing organisms as sources of fluorophores relieves the demand for petroleum feedstock in organic synthesis of fluorescent products, and endophytic fungi provide a promising vein for natural fluorescent products. We report the characterization of a pH-responsive fluorophore from an endophytic fungus isolated from sand pine. The endogenous fluorescence of the live organism was measured using fluorescence microscopy. Computational interpretation of the spectra was accomplished with time-dependent density functional theory methods. The combined use of experimental and theoretically predicted spectra revealed the pH equilibria and photoexcited tautomerization of the natural product, 5-methylmellein. This product shows promise both as a stand-alone pH-indicating fluorophore, with alkaline pKa , and as "green" feedstock for synthesis of custom fluorophores.

Low-temperature time-resolved phosphorescence excitation emission matrices for the analysis of phenanthro-thiophenes in chromatographic fractions of complex environmental extracts.

The present study investigates the analytical potential of low-temperature photoluminescence spectroscopy for the analysis of seven phenanthrothiophenes with molecular mass 234 g mol-1. The studied PASHs include Phenanthro [1,2-b]thiophene, Phenanthro [2,1-b]thiophene, Phenanthro [2,3-b]thiophene, Phenanthro [3,2-b]thiophene, Phenanthro [3,4-b]thiophene, Phenanthro [4,3-b]thiophene and Phenanthro [9,10-b]thiophene. Excitation and emission spectra recorded from n-alkane solutions at room temperature, 77 K and 4.2 K show phosphorescence emission from all the studied isomers at cryogenic temperatures. The analytical figures of merit obtained under steady state (fluorescence) and time-resolved (phosphorescence) conditions provide limits of detection at the parts-per-billion (ng mL-1) concentration levels. Processing 77 K and 4.2 K phosphorescence data with parallel factor analysis showed to be a robust approach to the determination of phenanthro-thiophenes in complex fluorophore mixtures.

A critical viewpoint on current issues, limitations, and future research needs on micro- and nanoplastic studies: From the detection to the toxicological assessment.

Increasing scientific attention on the presence of micro- and nanoplastics (MNPs) in the environments and their potential toxic effects on humans and the ecosystems is evident. Accordingly, the number of publications on this topic has increased substantially from only 5 in 2010 to more than 850 in 2019. Thus, this critical review aimed at providing state-of-the-art information on the existing methods for characterization and detection of MNPs in various matrices, as well as the reported toxic effects of MNPs in both in vivo and in vitro systems, anticipating challenges and providing future needs to improve the current scientific knowledge. We performed a systematic search of recent literature on available methodologies for the characterization/detection of MNPs in different samples, and the summary of such protocols is provided. Also, the existing procedures for in vitro and in vivo toxicity evaluation of MNPs were critically described. The results of our search revealed that quite a great deal of effort had been made to detect, characterize, and quantify the fate and effect of MNPs. However, we are still far from a complete understanding of behaviors of MNPs in the environments and biological systems. Thus, there is a need to advance the existing protocols to improve data accuracy. Besides, more studies that focus on uptake kinetics, accumulation, and biodistribution of MNPs in biological systems are required.

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.