Examination of petroleum products of high relative molecular mass for forensic purposes by synchronous fluorescence spectroscopy. Part I. Appraisal of experimental factors

Abstract

The luminescence of petroleum derivatives is discussed with reference to a standard technique for their differentiation based on synchronous fluorescence spectroscopy. The spectra are highly sensitive to quenching by oxygen and by halogenated compounds; for general-purpose use, solutions of samples (in hydrocarbon solvents) must be deoxygenated. Although the quantum yield of the fluorescence is of the order of 0.15, the fluorescence is distributed over a wide wavelength range and, at the sample concentrations usually required in order to obtain satisfactory spectra, significant inner filter effects are often present and corrections must be made for these. Various spectral features that differ between samples are defined. After correction for instrumental and inner filter effects, the features are expressed numerically for evaluation and use in the pattern recognition study that will be described elsewhere in Part II. Examples of other types of spectra are considered in relation to the standard technique. These are synchronous and conventional fluorescence contour diagrams, synchronous derivative spectra, low-temperature synchronous fluorescence spectra and phosphorescence spectra.