Coulometric total carbon dioxide analysis for marine studies: Automation and calibration

An automated instrument for the coulometric detection of total carbon dioxide (TCO₂) was developed from the manual prototype of Johnson et al. Pure CO₂ was used to calibrate the detector, the whole analytical procedure was controlled by a microcomputer, and the unit was compact enough for field and shipboard use. Some 67 samples from the Askö field station on the Baltic Sea (salinity = 6; TCO₂ ranging from 1224.3 to 1276.1 μmol l^?1 with a mean of 1245.6 μmol l^?1) and 31 samples from Swedish lakes (TCO₂ ranging from 19.5 to 252.3 μmol l^?1 with a mean of 72.9 μmol l^?1) were analyzed. The pooled standard deviation of these analyses was ± 1.0 μmol l^?1 (% CV of 0.08 and 1.3%, respectively). Precisions of < 0.1% were routine for waters exceeding 1000 μmol l^?1 TCO₂. At Askö on the Baltic Sea, the mean absolute difference between coulometric and pH-alkalinity determinations of TCO₂ on 22 parallel samples was 6.7 μmol kg^?1 or 0.5% of the mean. Community metabolism studies gave maximum rates of net production (TCO₂ uptake) and respiration (TCO₂ production) of 0.9-1.2 and 0.3-0.5 μmol l^?1 b^?1, respectively. The results of this study provide solutions to the problems observed with the earlier manual prototype.