ASTM D4137-82(2004)

1.1 This practice describes the proper procedure for preserving phytoplankton samples with either formaldehyde or Lugol's solution

1.2 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Formaldehyde solution can be used as a permanent preservative of algae. Lugol’solution can be used to preserve algae for up to one year. Lugol’is a more suitable preservative for delicate algae such as naked flagellates.