Ultra-Violet Fluorescence (UVF) Screening Tool For On-Site Testing
Ultra-violet fluorescence (UVF) is used as a field screening tool in the on-site detection of a variety of compounds in soil and water, including PHCs, PCBs and PAHs. These are broad terms used to classify a number of compounds that are similar in structure. Petroleum products contain different types and amounts of hydrocarbons, which fluoresce differently.
Aromatic hydrocarbons, which include ringed shaped compounds such as benzene, both excite and emit energy at specific wavelengths. The analyser contains a mercury vapour lamp which also emits ultraviolet (UV) light. An excitation optical filter selects the optimal wavelength needed to energize the selected molecule of interest.
Once the molecules are in an excited state, they emit light as fluorescence when the molecule returns to its ground state. This fluorescence light goes through an emission optical filter which reduces the emitted light that comes in contact with the photomultiplier detector to those wavelengths specific to the molecule of interest. The fluorometer’s response to each sample is measured by the instrument on a linear, multi-point calibration curve.
UVF is used as a field screening tool, particularly useful in delineation of hydrocarbons during remediation. A typical sample can be prepared and tested in minutes, and the analyzer can be operated by a battery pack. This means that UVF is a valuable on-site testing technology and can be used on a wide range of sites, saving the client time and money – less time waiting for traditional lab results, and saves money by reducing the number of samples sent to the lab. In addition, it offers the environmental scientist and field engineers more information and a clear determination of the areas of impact.
While UVF can detect certain classes of compounds (E.g. diesel range hydrocarbons, gasoline range hydrocarbons), they are non-selective, in that all hydrocarbons of a certain range are detected, and cannot be separated out in the field. Laboratory analysis is required to determine concentrations of individual compounds.
Remedial activities can be directed on the basis of this field screening, and only confirmatory samples need to be sent to the lab, upon completion of the remedial activities.