Microplasma emission spectroscopy of stable isotope ratios in carbon dioxide

This study investigates the prospects of using emissions from the discharge of a stripline split-ring resonator microplasma source to measure the C-13/C-12 isotope ratio in CO2. The plasma source was used in a measurement scheme called microplasma emission spectroscopy, in which the visible emission spectrum of the CO2 discharge was investigated using a Charge- Coupled Device (CCD) spectrometer. The study revealed that the major isotope dependencies of the spectrum originated from the Angstrom system (B-1 Sigma(+) -> A(1)Pi) of CO molecules that had been converted from CO2 in the discharge. Although at least four of the bands of the Angstrom system showed clear isotopic dependences, the (0-3) band at 561 nm was concluded to show the most prospects for spectrometric applications because of a combination of wide isotopic shift and low background. A theoretical model of this band was constructed and used in a partial least squares fitting algorithm, to quantify the abundance of C-12 and C-13 in the sample. This signal processing method was shown to be robust and linear over the whole dynamic range of C-13/C-12 ratios (1%-100%) but required a ten-fold improvement in precision and accuracy at naturally occurring C-13 levels (1.07%-1.12%) to be useful in most scientific applications. However, several promising ways of achieving such an improvement have been presented, and the results demonstrate the potential of creating a simple, cost-effective, and highly miniaturized system for isotope ratio measurements, which could offer great advantages to scientists in many different fields, from environmental science to planetary exploration.