The samples are combusted in a pure oxygen environment, the gases mixed and separated by frontal chromatography. The separated gases are determined stepwise by a thermal conductivity detector. Precautions Care must be taken to ensure that contamination with PC and PN is avoided. Samples should, therefore, be kept away from paper, wood, food or other carbon-containing compounds. The filtration system that is set up to collect these samples is constructed of plastic.
Plastic contains carbon and, therefore, is a potential source of contamination.
The carboys and tubing used in this system must be kept clean and free of abrading surfaces. Sampling, Filtration and Storage 3.1. The samples are transferred via Tygon tubing which incorporates an in-line 202 um Nitex screen prefilter to remove zooplankton or any other rare particles which might otherwise affect the precision of the estimate. Once the rosette sampler is on deck, the vent valve of each Niskin bottle is opened and one end of the drawing tube is attached to the outflow spigot of the sampling bottle and the other end to the tubing connector on the cap of the filtration bottle. The filtration bottle valve is opened and 100-200 ml is run through the transfer tube and valve assembly to rinse the sampling bottle.