A Methods Manual for the Collection, Preparation and Analysis of ...

1.2 Pre-preparation examination of freshly sampled materialA quick examination of unpreserved fresh diatom material should be performed on return tothe laboratory to assess whether the diatom assemblage consists of predominantly of live cells(It should be noted dead cells will also form part of the bio-film and are not necessarilywashed away under natural conditions).If the majority of the diatoms in the freshly collected material are registered as dead cells(empty frustules with no chloroplasts) the sample should be discarded, as further analysis willnot give a true reflection of recent water quality at the particular sampling site.1.3 Cleaning techniques with rationaleAny method of preparation of diatoms for microscopy is acceptable, as long as the cleanedmaterial meets the following criteria: Concentrations of cells in the cleaned sample should match as closely as possible theconcentration of cells collected in the original sample. The organic matter in the sample should be completely removed. Foreign matter should either be absent or insufficient to cause problems during theenumeration or identification of the specimens.1.3.1 DecalcificationDecalcification is ONLY necessary if samples are to be later treated with nitric or sulphuricacid, as these acids combine with calcium causing the formation of an insoluble precipitate.This stage can be omitted if you are sure that the sample does not come from a site with anycalcareous rock in the catchment or if using the Hot HCl and KMnO 4 method(recommended technique)HEALTH AND SAFETYHydrochloric acid is CORROSIVE and OXIDATIVE. Do not perform anyanalysis using this chemical outside of a fume cabinet.When handling HCl wear acid resistant gloves, goggles and a lab coat.29