Preparing your sample for algal identification and counting Soon after the sample is collected the bottles must be clearly labelled with a waterproof pen. It is best to examine samples as early as possible after collection, while the algae remain alive because many features helpful in identifying algae are more clearly seen in live specimens. If you have to wait a few hours after collection to examine a sample it would be desirable to keep the sample cold on ice or in a portable refrigerator. However, in some instances, particularly for counting purposes, it is necessary to stain them and preserve the algae. If possible, therefore, identify the phytoplankton in your sample first, before staining them for counting.
Lugols solution is the preferred preservative and staining reagent.
Lugols solution may be available from chemical suppliers or chemists. The Lugols solution can be added to water samples drop by drop, using a Pasteur pipette. Note that Lugols solution has a shelf life of about 6 months. When the column of water appears clear, gently siphon off the top 90 mL without disturbing the sediment at the base of the cylinder. This means the phytoplankton present in 100 mL of the water have now been concentrated into 10 mL, resulting in a concentration factor of 10.