On-line technique for preparingand measuring stable carbon isotopeof total dissolved inorganic carbonin water samples ( d13CTDIC)

• Main Authors: S. Inguaggiato, F. Grassa, R. Favara, G. Capasso, L. Longo
• Format: Article
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2005-06-01
• Series: Annals of Geophysics
• Subjects: carbon isotope composition; Total Inorganic Carbon; Dissolved in water (TDIC); stable isotopes; continuous flow IRMS measurements; on-line extraction technique
• Online Access: http://www.annalsofgeophysics.eu/index.php/annals/article/view/3190

A fast and completely automated procedure is proposed for the preparation and determination of d13C of total
 inorganic carbon dissolved in water ( d13CTDIC). This method is based on the acidification of water samples transforming
 the whole dissolved inorganic carbon species into CO2. Water samples are directly injected by syringe
 into 5.9 ml vials with screw caps which have a pierciable rubber septum. An Analytical Precision «Carbonate
 Prep System» was used both to flush pure helium into the vials and to automatically dispense a fixed amount of
 H3PO4. Full-equilibrium conditions between produced CO2 and water are reached at a temperature of 70°C
 (± 0.1°C) in less than 24 h. Carbon isotope ratios (13C/ 12C) were measured on an AP 2003 continuous flow mass
 spectrometer, connected on-line with the injection system. The precision and reproducibility of the proposed
 method was tested both on aqueous standard solutions prepared using Na2CO3 with d13C=-10.78 per mil versus
 PDB (1 s= 0.08, n = 11), and at five different concentrations (2, 3, 4, 5 and 20 mmol/l) and on more than
 thirty natural samples. Mean d13CTDIC on standard solution samples is ?10.89 < per mil versus PDB (1 s= 0.18,
 n = 50), thus revealing both a good analytical precision and reproducibility. A comparison between average
 d13CTDIC values on a quadruplicate set of natural samples and those obtained following the chemical and physical
 stripping method highlights a good agreement between the two analytical methods.