Simultaneous 13 C/ 12 C and 18 O/ 16 O isotope ratio measurements on CO 2 based on off-axis integrated cavity output spectroscopy

Authors: Jost, Hans-Jürg¹; Castrillo, Antonio²; Wilson, H. William³

Source: Isotopes in Environmental Health Studies, Volume 42, Number 1, Number 1/March 2006 , pp. 37-45(9)

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Abstract:

A prototype off-axis integrated cavity output spectrometer (OA-ICOS) utilizing two identical cavities together with a near-infrared (1.63 µm) external cavity tunable diode laser is described. The two-cavity design—one for a reference gas and one for a sample gas—takes advantage of classical double-beam infrared spectrometer characteristics in reducing uncertainties due to laser scan or power instabilities and major temperature variations by a factor of three or better compared with a single-cavity scheme. This is the first OA-ICOS instrument designed to determine 13 C/ 12 C and 18 O/ 16 O ratios from CO 2 rotation/vibration fine structure in three different combination bands. Preliminary results indicate that at 0.8 Hz a precision of 3.3 and 2.8 permil is obtained for d 13 C and d 18 O, respectively, over a period of 10 h and a pure CO 2 gas sample at 26 hPa. By averaging 100 spectra over a subset of the data, we achieved a precision of 1.6 and 0.8 permil for d 13 C and d 18 O, respectively.

Keywords: Carbon-13; Carbon dioxide; IR spectroscopy; Laser; Measurement; Oxygen-18

Document Type: Research article

DOI: http://dx.doi.org/10.1080/10256010500503163

Affiliations: 1: Bay Area Environmental Research Institute, 560 Third Street W., Sonoma, CA, 95476, USA 2: Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Via Vivaldi 45, 81100, Caserta, Italy 3: Department of Chemistry, Western Washington University, 516 High Street, Bellingham, WA, 98225, USA

Publication date: 2006-03-01