Developing an optimal path fluorescence scanning method for identification of PAHs in mixtures

Fluorescence spectroscopy is among the most commonly used methods that for analytic studies. The quality of the measured fluorescence data is dependent on various technical parameters. Among them are the excitation intensity, the bandwidths of the slits, the sensitivity of the detector, and the number of scanned wavelengths where the analyte emits. The shortest scanning mode is a single point measurement, which is very short and has the lowest potential to inflict photodamage to the analyte. however, such method may be blind to measurements errors since it does not show the whole peak of the analyte. The most common scanning method is the emission scan, in which λEx is fixed and λEm is variable. A less common method is excitation scan in which λEx is variable and λEm is fixed. Both methods may be restricted by the light scattering of the lamp at wavelengths that are close to the excitation and its double value. A more advanced method is synchronous fluorescence in which λEx and λEm varies during the scan with a constant gap between them. This method is less restricted by the lamp scattering and also display narrower peaks. The most comprehensive scanning method is excitation-emission matrixes that measure the whole fluorescence map. However, while using a system with a photo-multiplier detector, the scan time may be relatively long and cause photodamage to the analyte. In this work, we demonstrate a new scanning method named optical path fluorescence in which the scanning path is conducted from the maxima of the peaks toward their shortest way down to the noise level. We show that upon addition of increasing artificial noise levels, the optimal path method can predict the concentrations of the 3-polyaromatic hydrocarbons in a mixture better than all other scanning methods.