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Alcohol

(See von Stosch, 1974)

Note. A drop of the cleaned sample in distilled water is left to dry on a coverslip (0.17 ± 0.02 mm thick) cleaned with alcohol. The medium is applied to the dry sample and left to dry. The cover slip is "picked up" by pressing a cleaned microscope slide gently toward it. Thereafter, the slide with the cover slip is heated to ca. 50-70°C for a few minutes to remove air bubbles and harden the medium. Rinsed but not cleaned material to be embedded in Pleurax has to first be brought into 100% alcohol. The sample is then concentrated to near dryness, mixed with Pleurax, and put onto a coverslip. The coverslip is placed face down on a microscope slide and left to dry at room temperature or gently heated on a hot plate till the solvent has evaporated. Addresses of manufacturers cited: G. T. Gurr Ltd/Baird and Tatlock Ltd, Freshwater Road, Chadwell Heath, Romford, Essex RM1 1HA, UK; Northern Biological Supplies, 31 Cheltenham Avenue, Ipswich, Suffolk IP1 4LN, UK.

Note. A drop of the cleaned sample in distilled water is left to dry on a coverslip (0.17 ± 0.02 mm thick) cleaned with alcohol. The medium is applied to the dry sample and left to dry. The cover slip is "picked up" by pressing a cleaned microscope slide gently toward it. Thereafter, the slide with the cover slip is heated to ca. 50-70°C for a few minutes to remove air bubbles and harden the medium. Rinsed but not cleaned material to be embedded in Pleurax has to first be brought into 100% alcohol. The sample is then concentrated to near dryness, mixed with Pleurax, and put onto a coverslip. The coverslip is placed face down on a microscope slide and left to dry at room temperature or gently heated on a hot plate till the solvent has evaporated. Addresses of manufacturers cited: G. T. Gurr Ltd/Baird and Tatlock Ltd, Freshwater Road, Chadwell Heath, Romford, Essex RM1 1HA, UK; Northern Biological Supplies, 31 Cheltenham Avenue, Ipswich, Suffolk IP1 4LN, UK.

this treatment, useful information, especially on the girdle, can be obtained. Freeze-drying (Williams, 1953) is an alternative, but the most reliable results are obtained with critical point drying (Cohen, 1974). The equipment and methods are developed for general use and not especially for diatoms. For diatoms particular vessels to contain the sample during the drying have to be constructed. The end product is usually a dry powder that subsequently may be further prepared for SEM or TEM.

On a routine basis acid-cleaned material prepared for LM is used for both TEM and SEM. For TEM, a drop of an aqueous suspension of cleaned material is put onto a formvar-coated copper grid (Sournia, 1978, p. 138). After air drying, it can be studied with TEM without further treatment. The same procedure can be followed for SEM, except that the sample suspension is put onto a small glass coverslip or other smooth material. After air drying, the material has to be coated with a metal (usually Au/Pd, Pt) film in an evaporating or sputter device.

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