A simple automated continuous-flow-equilibration method for measuring carbon monoxide in seawater

A simple, robust, low-maintenance method using air-segmented continuous-flow equilibration was developed and automated to measure carbon monoxide (CO) in natural waters precisely and accurately. Finely regulated flows of CO-free air and of seawater or standard water were pumped into a glass coil, forming discrete gas/liquid segments. The partially CO-equilibrated gas effluent was injected into a Trace Analytical reduction analyzer for CO detection. A semiempirical mass-balance model was established for predicting and optimizing the performance of the CO extractor. The optimized gas and water flow rates were ∼1.2 and ∼14 mL min^-1, respectively, giving a response time of less than 15 min and a CO-extraction yield of∼80%. The analytical blank, precision, and accuracy were, respectively, 0.02 nM, ± 2.5% (at the ∼1 nM level), and better than 5%. Two extractors can be interfaced to one detector at 4-6 samples per hour for each extractor. Coupled with a continuous surface-water sampler, the system was successfully applied to monitoring the diurnal variation of CO concentration in Sargasso Sea surface waters.