Sub-Sampling Technique for the Determination of Particulate-Phase Organic Carbon in Water

Abstract A procedure for determining particulate-phase organic carbon (POC) in water was developed and applied to the analysis of samples from the Laurentian Great Lakes of North America. Water samples were filtered through 0.7 μM pore-size glass fiber filters which were sub-sampled to introduce measurable quantities of paniculate matter into a Carlo Erba EA-1108 elemental analyzer. The sub-sampling technique allowed quick filtration of water samples, typically 1 to 4 liters for open-lake locations, using 47 mm diameter filters while meeting the small size requirement of the combustion chamber. The detection limit of the instantaneous combustion procedure was 2.9 μg of carbon per sub-sample, which translates to 28 μg/L POC for a sample volume of 1 liter. The precision of the sub-samples averaged 6.2% coefficient of variation (CV), which was comparable to the precision of replicate water samples (6.6% CV).