A FIELD AND LABORATORY PROCEDURE TO COLLECT, PROCESS, AND PRESERVE FRESH-WATER SAMPLES FOR DISSOLVED ORGANIC-CARBON ANALYSIS

I tested each step required to prepare freshwater samples for dissolve d organic C (DOC) analysis, including collection, filtration, preserva tion, and storage. I placed particular emphasis on finding a protocol that was amenable for use at remote field sites as well as in the labo ratory. A portable and manual syringe-type sample collection and filtr ation system was free of artifacts and yielded filter blanks of <5 mug C liter-1. Analysis of 5 yr of streamwater DOC data showed an average relative precision of 2% for the total procedure from sample collecti on through analysis by persulfate oxidation. Sample volumes of 100 lit ers or more were processed with a cartridge filtration system that gav e results equivalent to syringe filtration. It is possible to store sa mples preserved with acids or biocides at room temperature for 2 weeks to 1.5 yr with only a 1-11% reduction in accuracy.