A newly developed macro flow planktometer is described for measuring plankton organisms with a size of 100-2,000 pm by the flow principle in timesaving and noncontact fashion. Based on the method of changes in electric resistance (Coulter principle), the device allows determination of the body volume of living organisms in their natural medium (fresh or seawater) at a measuring rate of up to 50 organisms per second. Simultaneous, laser-excited fluorescence measurement permits quantitative detection of fluorescent substances within the organisms. Controlled by the multiparametric measurement, video images of organisms of particular interest can be taken in the flow chamber using a stroboscopic imaging system. Valuable morphological information on the material under test is thus available in addition to the analytical measurement. Data acquisition and imaging, the total system control, and the fast data evaluation are performed with an IBM-AT compatible computer using an extensive software package. The easy-to-handle desktop unit can be used both in land laboratories and on ships. The modular structure of the system permits any desired combination of individual components to adapt it to various requirements. The operability of this new measuring system is demonstrated by several applications.

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