Development of a near-IR laser based spectrometer for continuous measurement of stable carbon isotopes in CO 2

Abstract

A near-IR laser based spectrometer for continuous measurement of stable carbon isotopes in CO 2 has been developed. 12CO 2 and 13CO 2 are detected with wavelength modulation spectroscopy and a Herriott-type multi-pass cell with a optical path length of 29.9 m using a distributed feedback laser diode in the 2-μm wavelength region. To measure the isotope ratio precisely, the influence of pressure and temperature variation in δ 13C was evaluated. The limit of detection for 12CO 2 in our system was 16 ± 1 ppbv. The precision in the determination of δ 13C was 0.1%o for 120 seconds signal integration time at ambient concentration levels. We demonstrate that our system enables automated continuous measurements of δ 13C of CO 2 in ambient air without any complex operation by users. © 2012 The Japan Society of Mechanical Engineers.