PIGMENT CONTAMINANTS IN POLYCARBONATE FILTERS

Membrane filters are often used to size fractionate phytoplankton when measuring biomass-specific production. Polycarbonate filters are reputed to have the lowest extractables for membranes used for environmental analysis, however, we show that Nuclepore(R) polycarbonate filters contain a dye that co-extracts with algal pigments into methanol. The contaminating dye has characteristics similiar to those of pigments extracted from mixed populations of naturally occurring phytoplankton when measured spectrophotometrically. The dye can, however, be separated from the chlorophylls using high performance liquid chromatography. In addition, the dye does not fluoresce and hence does not interfere with fluorometric analysis of chlorophyll a. The purpose of this note is to alert investigators to the presence of the contaminating pigment in Nuclepore(R) polycarbonate filters which can be mistaken for algal pigments. Other brands, such as Poretics(R), do not contain the contaminant and could be used as an alternative.