Microcystins are cyclic peptides specified in the Hygiene Testing Methods, and are readily retained on silica-based solid-phase discs (Empore Disk C18) and polymer-based Empore Disc SDB. If the sample contains large amounts of algae, such as lake water, it is recommended that the filtrate be extracted directly using a solid phase after filteration through a glass membrane filter, and that the algae on the filter be ultrasonically extracted with a 5 % acetic acid solution. In order to eliminate contaminants from the sample, it is recommended that it is cleaned-up with a silica-gel solid phase if necessary.