Isotopic carbon analysis provides a valuable tool for studies of metabolic pathways and for tracing carbon transformations in the environment. This project will attempt to develop an optical technique for the convenient measurement of carbon isotopic (13C/12C) ratios. The instrument will utilize a linear photodiode array to image the spectra arising from plasma emission of the carbon-containing molecules. Spectral processing algorithms will be applied to remove spectral interferences and to correct for apparent isotopic ratio shifts due to variations in sample pressure and power coupling. In this Phase I study, the optimal bandheads for isotopic ratio determination using the CO molecule will be identified. The criteria will include a minimal contamination from other transitions of the 12C isotope. Different excitation sources and sample preparation techniques will be studied with the intent of coupling the instrument to an automated carbon-nitrogen analyzer in the Phase II work. The results of the Phase I effort are expected to result in the ability to determine the isotope ratio of carbon to a precision of 0.01% or 0.1 & unit which would make the method applicable to both natural abundance studies and tracer addition studies. The relative simplicity and low cost of this instrument compared to mass spectrometers will greatly expand the applications of isotopic abundance measurements. Aerodyne is a known positive performer and will provide excellent support for the work. The product, when available, should find considerable use in ecological studies requiring the processing of large numbers of carbon isotope ratio samples.
