Automated spectrophotometric determination of carbonate ion concentration in seawater using a portable syringe pump based analyzer

Highlights
• First fully automated determination of carbonate ion concentration in seawater

• A flow batch analyzer with laboratory-made hardware and software

• 13-day real-time underway determination of carbonate ion in the South China Sea

• High resolution field seawater analysis with rare maintenance

Abstract
Observations of seawater carbonate ion concentrations are critical to assess the ecological effects of ocean acidification. Nevertheless, currently available methods are labor intensive or too complex for field applications. Here, we report the design and performance of the first fully automated portable carbonate ion analyzer. Measurements are based on reaction of carbonate and chloride ions with Pb(II) followed by quantitative UV spectrophotometric detection of the PbCO30 complex. The core hardware is a syringe pump equipped with a multi-position valve that is controlled by software written in LabVIEW. Measurement precision is 1.1% (n = 13) with a measurement frequency of 12 h−1. The analyzer was used to continuously monitor carbonate ion concentration variations in a 2500 L coral reef tank for five days (test 1), and used for shipboard underway and vertical profile analysis during a 13-day cruise (test 2). The analyzer attained a combined standard uncertainty of 3.0%, which meets the Global Ocean Acidification Observing Network’s “weather level” goal. Through use of a syringe pump mechanism for mixing seawater and reagent solution, the analyzer is robust, functionally flexible, and quite suitable for continuous environmental monitoring under harsh conditions.

Shangguan Q., Shu H., Li P., Lin K., Byrne R. H., Li Q., Yuan D. & Ma J., in press. Automated spectrophotometric determination of carbonate ion concentration in seawater using a portable syringe pump based analyzer. Marine Chemistry. Article (subscription required).

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