Microplasma emission spectroscopy of stable isotope ratios in carbon dioxide

Abstract

This study investigates the prospects of using emissions from the discharge of a stripline split-ring resonator microplasma source to measure the 13C/12C 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 Ångström system (B 1Σ+ → A 1Π) of CO molecules that had been converted from CO2 in the discharge. Although at least four of the bands of the Ångström 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 12C and 13C in the sample. This signal processing method was shown to be robust and linear over the whole dynamic range of 13C/12C ratios (1%–100%) but required a ten-fold improvement in precision and accuracy at naturally occurring 13C 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.