Design and application of a multichannel laser-induced fluorescence system for environmental monitoring.

摘要

Laser induced fluorescence (LIF) spectroscopy is an analytical technique that provides superior sensitivity. It has been widely used in applications encompassing chemical, biological, physical, environmental, and pharmaceutical research. Combined with the use of cone penetrometer testing (CPT) technology and optical fibers, it has become a time- and cost-effective tool for environmental screening. By incorporating ten laser wavelengths simultaneously and collecting a full three-dimensional fingerprint (i.e. excitation-emission matrix, or EEM) of the soil sample, research conducted in our group has taken the technique one step further by providing improved specificity and better quantification of subsurface contaminants.; Our current multichannel LIF probe has been redesigned to provide improved rejection of scattered excitation light, and to reduce probe size and sampling area. This probe was assembled on a CPT rod, and the LIF-CPT system is capable of collecting EEMs at a rate of 1 EEM every 2 seconds. Two methods have been used to interpret the EEM data. First, total fluorescence was used to indicate the presence of total petroleum hydrocarbons (TPH). Second, and more importantly, individual target species were identified and their concentrations quantified approximately. This was achieved initially by analyzing the signal at the characteristic fluorescence peak wavelength of a compound, and later by analyzing the entire EEM using chemometrics methods.; The system has been field-demonstrated at Hanscom Air Force Base (AFB) and Otis Air National Guard Base (ANGB). In situ LIF measurements were used to map the contamination of the sites, achieving a vertical resolution of approximately 2 cm. In addition, core samples were taken and analyzed by both on-site LIF and off-site laboratory analyses with standard methods and their results are compared as a measure of validating the LIF-EEM-CPT technique. Qualitative and semi-quantitative agreement between these two sets of results were obtained.; In this work, the design of a newer version of the optical fiber probe, the integrated LIF-CPT instrument, the demonstration of the system, the EEM data analysis methods, and the analysis results obtained in the laboratory and in the field are described.