| dc.description |
An autonomous, in-situ instrument was developed to detect dissolved
copper in seawater, suitable for deployment on time scales from weeks to months.
A commercially available in-situ nitrate analyzer (YSI 9600) was adapted to
measure copper (II) in seawater by chemiluminescence. Modifications included
construction of a photomultiplier (PMT) based detector and flow-cell, the use of
more chemically resistant plastics for parts in contact with the reagents, addition
of an in-line acidification step and optimization of the method and flow
parameters. Filtration to 0.45μm and acidification online (pH ~1.7) produces a
measurement of total dissolved Cu(II). Calibration is achieved by periodically
analyzing ligand-stabilized seawater standard and blank solutions stored at pH 8
and acidified online. Micro solenoid pumps take in sample and dispense reagent,
standard, and blank solutions, which are stored in 1L plastic bags. All waste is
collected in two 5L bags. In-situ, the instrument has an average detection limit of
0.8(3) nM, a sample precision of 7%, and an accuracy, assessed over all
deployments, of 17%. The instrument is capable of functioning autonomously for
25 days sampling every hour and calibrating every six hours, with reagent
consumption being the limiting factor. |
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