Shpol'skii spectroscopy at the interface of two non-polar microenvironments: a novel approach for the analysis of polycylic aromatic compounds

Room-temperature excitation–emission phosphorescence matrices and second-order multivariate calibration for the simultaneous determination of pyrene and benzo[a]pyrene

The present article describes the simultaneous phosphorimetric determination of pyrene and benzo[a]pyrene, two highly toxic polycyclic aromatic hydrocarbons, through excitation-emission phosphorescence matrices (EEPMs) and second-order calibration. The developed approach enabled us to determine both compounds at microg L(-1) concentration levels without the necessity of applying separation steps, as well as significantly reducing the experimental time. An artificial neural network (ANN) approach was applied to optimize the chemical variables which have an influence on the room-temperature phosphorescence emission of the studied analytes. The present study was employed for the discussion of the scopes of the applied second-order chemometric tools: parallel factor analysis (PARAFAC) and partial least-squares with residual bilinearization (PLS/RBL). The superior capability of PLS/RBL to model the profiles of other potentially interferent polycyclic aromatic hydrocarbons (PAHs) was demonstrated. The quality of the proposed method was established with the determination of both pyrene and benzo[a]pyrene in artificial and real water samples.

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.

Solid-liquid extraction fluorescence line narrowing spectroscopy of fluoroquinolones in aqueous samples

We present a simple, selective, and sensitive method for the analysis of fluoroquinolones in water samples without previous separation. Octadecyl silica membranes are used with the dual purpose of sample preconcentration and solid substrate for fluorescence line narrowing spectroscopy. Measurements at liquid helium temperature (4.2 K) are easily made with the aid of a cryogenic fiber-optic probe. The entire procedure takes less than 15 minutes per sample and it consumes only 100 microL of organic solvent. Unambiguous fluoroquinolone determination is accomplished via wavelength-time matrices, which provide simultaneous information on spectral peak purity and fluorescence lifetime. We show that 10 mL of water sample are enough to detect analyte concentrations at parts-per-billion levels. The potential of this approach for the analysis of real world samples is demonstrated with the analysis of a synthetic mixture of seven fluoroquinolones spiked in a heavily contaminated water sample.

Instrumentation for Multidimensional Luminescence Spectroscopy and Its Application to Low-Temperature Analysis in Shpol'skii Matrixes and Optically Scattering Media

We present a single instrument with the capability to collect multidimensional data formats in both the fluorescence and the phosphorescence time domains. We also demonstrate the ability to perform luminescence measurements in highly scattering media by comparing the precision of measurements in Shpol'skii solvents to those obtained in "snowlike" matrixes and solid samples. For decades, conventional low-temperature methodology has been restricted to optically transparent media. This restriction has limited its application to organic solvents that freeze into a glass. We remove this limitation with the use of cryogenic fiber-optic probes.

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).