QUANTITATIVE-DETERMINATION OF PARTICLE CONCENTRATIONS IN EXPERIMENTALAND MARINE ENVIRONMENTAL-SAMPLES

As the application of flow cytometry increases across the environmenta l sciences, there is a need to expand instrument flexibility. In parti cular, some of the major applications within aquatic research demand a n ability to quantify the particles under investigation, expressing th em as numbers per unit of sample volume. Two of the principal areas of flow cytometric investigations are the characterisation of naturally occurring particulate assemblages in the oceans and investigations int o the feeding behaviour of ''filter feeding'' organisms on the mixture s of such particles. In both cases some of the most useful data derive d from flow cytometry require that analyses be determined in terms of particle concentrations. Therefore, a simple and practical modificatio n is described, which allows known sample volumes to be analysed on fl ow cytometers. The method has a high degree of flexibility in sample v olume and is cost effective and reliable. It involves introducing a st andard chromatography ''loop injection valve'' into the sample-handlin g fluidics system. Use of fluorescent beads shows that a range of part icle sizes and concentrations can be used with this system. Tests, als o using fluorescent beads and an algal culture, show that replicate 10 0 mu l sample volumes can be analysed and counted with a coefficient o f variation of less than 3%. (C) 1994 Wiley-Liss, Inc.