Application of Ultraviolet Spectroscopy for Monitoring Oil in Water
Defence Research Establishment Atlantic Dartmouth, Nova Scotia Canada
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This paper will discuss the usefulness of ultraviolet spectroscopy for determination of low levels of oil in water. The presentation will include the findings of a laboratory study and relate this work to the use of ultraviolet spectroscopy in the detection of oil in water from oil rig discharges, tanker discharges and oil spills at sea. The test program was essentially a matrix test where different types of oil diesel, naval distillate, lubricating oil and hydraulic oil were mixed at concentrations from 0 to100 ppm and detected using various wavelengths for ultraviolet absorbance and ultraviolet fluorescence. Limits of detection, linearity, interference, and phase effects i.e. dissolved versus particulate oil were assessed. The results indicated that both ultraviolet absorbance and fluorescence could detect oil in water at 1 ppm, though experience indicated that fluorescence was about one order of magnitude more sensitive. The linearity of response was acceptable for both detection methods over the range 0 to 25 ppm. Beyond this range both methods tended to significantly under report the oil present. Interference from bilge cleaners, solids and other chemicals were very pronounced for ultraviolet absorbance, but were almost nonexistent for ultraviolet fluorescence. These interference results were consistent with previous site experiences testing Oil Detection Monitors on various oil tankers and in other similar applications. The major problem with all Oil Detection Monitors with regard to calibration was reconfirmed for these detection formats. The response of the detector varies depending on the type of oil present. Thus the calibration of a unit to produce accurate readout of part per million oil in water is very problematic. Experience in the field with existing oil tanker or rig discharges show that where a variety of oils may be present the Oil Detection Monitors are often inaccurate, and generally under report significantly.