High temperature combustion UV-fluorescence
This technique is widely used for diesel blending operations due to its good precision and involves fluorescence spectroscopy. High temperature combustion UV-fluorescence resembles dry colorimetry as both imply combustion of the hydrocarbon stream in the sample and produce CO2, H2O and SO2. After the combustion, carbon dioxide and water are removed. The difference between the two methods is that this technique measures SO2 by ultraviolet fluorescence. As SO2 enters the reaction cell, it is exposed to ultraviolet radiation. As a result, SO2 absorbs some of this energy and goes to an excited state. When this molecule returns to its ground state, light is emitted at a particular wavelength. A photomultiplier tube measures the intensity of this light that is directly proportional to the concentration of SO2 present in the sample. Although this technique measures SO2 concentrations at low detection levels (PPB), this technique still requires a reference detector because it suffers from U.V. lamp intensity deterioration.