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Sample preparation
Water samples (l00ml approx) are concentrated onto 25 mm diameter Nuclepore filters
(0.4 JLm) by filtration at low vacuum pressure. Particles collected on the filter are transferred
onto a gelatin-coated microscope slide. The filter is removed and the transferred sample is
covered with few drops of a 30% glycerol aqueous solution and a cover slip. Samples are kept
frozen at -20°C until analysis. The absorption and fluorescence properties of cells remain
unaltered when samples are stored frozen at -20°C indefinitely and do not change their
properties when brought back to room temperature for analysis.
ABSORPfION
The technique has a spectral resolution comparable to traditional spectrophotometric
measurements allowing the simultaneous determination of particle type, cross-sectional area
(G), and the absorption efficiency factor (Q.(A» for a single particle. The application of
microphotometry to field samples enables variations of absorption properties within the
particulate assemblage to be directly assessed, allowing discrimination of major absorption
bands corresponding to the algal pigments: chlorophyll a at 435 and 675 nm, chlorophyll b
at 470 and 650 nm, chlorophyll cat 465 and 630 nm, and fucoxanthin and peridinin from
470 nm to 550 nm. The spectra may be used to fingerprint taxonomic differences between
algal cells or characterize detrital particulates (Fig. 2).
Microphotometric detenninations
Measurements of the spectral transmittance of individual particles are determined by focusing
on the targeted particle and selecting an appropriate optical slit so that a representative
cross-sectional area of the particle is sampled. The minimum practical target area that can be
sampled by the present system is in the range of 3 JLm diameter.
The spectral transmittance of individual particles is determined by focusing on the targeted
particle. An adjacent particle-free area is used as the blank transmittance. Measurements of
Sample preparation
Water samples (l00ml approx) are concentrated onto 25 mm diameter Nuclepore filters
(0.4 JLm) by filtration at low vacuum pressure. Particles collected on the filter are transferred
onto a gelatin-coated microscope slide. The filter is removed and the transferred sample is
covered with few drops of a 30% glycerol aqueous solution and a cover slip. Samples are kept
frozen at -20°C until analysis. The absorption and fluorescence properties of cells remain
unaltered when samples are stored frozen at -20°C indefinitely and do not change their
properties when brought back to room temperature for analysis.
ABSORPfION
The technique has a spectral resolution comparable to traditional spectrophotometric
measurements allowing the simultaneous determination of particle type, cross-sectional area
(G), and the absorption efficiency factor (Q.(A» for a single particle. The application of
microphotometry to field samples enables variations of absorption properties within the
particulate assemblage to be directly assessed, allowing discrimination of major absorption
bands corresponding to the algal pigments: chlorophyll a at 435 and 675 nm, chlorophyll b
at 470 and 650 nm, chlorophyll cat 465 and 630 nm, and fucoxanthin and peridinin from
470 nm to 550 nm. The spectra may be used to fingerprint taxonomic differences between
algal cells or characterize detrital particulates (Fig. 2).
Microphotometric detenninations
Measurements of the spectral transmittance of individual particles are determined by focusing
on the targeted particle and selecting an appropriate optical slit so that a representative
cross-sectional area of the particle is sampled. The minimum practical target area that can be
sampled by the present system is in the range of 3 JLm diameter.
The spectral transmittance of individual particles is determined by focusing on the targeted
particle. An adjacent particle-free area is used as the blank transmittance. Measurements of