This chapter describes the design, construction and deployment of a shipborne facility intended to minimize trace metal contamination during the sampling and initial processing of open ocean water samples Results obtained to date confirm the overall success of the approach, both in absolute values for trace metal concentrations and in relation to the nutrient and other data obtained from the same samples.

HISTORICAL BACKGROUND

During the past 100 years the apparent concentrations of many trace elements in sea water have shown a considerable decrease, with current values, which are considered to be accurate, typically at nano- and picomole 1−1 levels Part of this decrease can be accounted for by improvements in analytical techniques, particularly the advent of graphite furnace atomic absorption spectrophotometry and electrochemical techniques (compare, for example, methods in refs 1 to 5) With these advances in analytical capability it has become increasingly obvious that contamination from reagents and containers used in analyses may be an important factor in data obtained and that the scrupulous use of clean techniques is required to ensure adequate precision, accuracy, and detection limits (refs 6 to 8).

As the improvements in analytical technique cited above took place, two further major sources of errors in data became apparent adventitious contamination from the use of inappropriate sampling materials and techniques, and loss of metals from samples by adsorption on to container walls The latter problem can generally be controlled, for filtered samples, by acidifying to pH < 2 prior to storage To avoid contamination sample collection has to be via a clean and metal-free system The use of plastic or rubber components containing metal fillers must be strictly avoided Teflon is potentially the cleanest constructional material; however, it is expensive and poses mechanical problems (ref 9) Generally acceptable substitutes include polyethylene, polypropylene and polymethylmethacrylate (Perspex) (ref 6).

Material from steel hydrowires, associated lubricants and surface slicks, often derived from the sampling ship, can contaminate sampling bottles On recovery of a representative water sample, its initial processing (e g filtration, transfer to storage containers, and preservation) on board a ship not specially prepared is carried out in an environment likely to be rich In potential s carried out A particularly appropriate and convenient solution is the use of a containerized clean laboratory.

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