Combining Cryogenic Fiber Optic Probes with Commercial Spectrofluorimeters for the Synchronous Fluorescence Shpol'skii Spectroscopy of High Molecular Weight Polycyclic Aromatic Hydrocarbons

Abstract

Cryogenic fiber optic probes are combined for the first time with a commercial spectrofluorometer for Shpol'skii spectroscopy measurements at liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures. Accurate and reproducible acquisition of fluorescence spectra and signal intensities is demonstrated with three well known Shpol'skii systems, namely, anthracene/heptane, pyrene/hexane, and benzo[a]pyrene/octane. The ability to adjust the excitation and emission bandpass of the spectrofluorimeter to reach both site-resolution and analytically valuable signal-to-noise ratios was illustrated with benzo[a]pyrene in n-octane. The analytical potential of 4.2 K synchronous fluorescence Shpol'skii spectroscopy for the analysis of high molecular weight–polycyclic aromatic hydrocarbons was then explored for the first time. The judicious optimization of wavelength offsets permitted the successful determination of dibenzo[ a,l]pyrene, dibenzo[ a,e]pyrene, dibenzo[ a,h]pyrene, dibenzo[ a,i]pyrene, and naphtho[2,3- a]pyrene without previous chromatographic separation from a soil extract with complex matrix composition. The simplicity of the experimental procedure, the competitive analytical figures of merit, and the selectivity of analysis turn 4.2 K synchronous fluorescence Shpol'skii spectroscopy into a valuable alternative for screening isomers of high molecular weight polycyclic aromatic hydrocarbons in environmental samples.