Handling and Preservation of Water Samples


HNU-WATERSS Laboratory

Waters are susceptible to change as a result of physical, chemical or biological reactions which may take place between the time of sampling and the analysis. If precautions are not taken, at the time of sampling, changes may occur rendering analytical data unrepresentative.

Changes may occur due to:

  • consumption of certain constituents by bacteria, algae etc.,
  • certain compounds being oxidised by the dissolved oxygen in the sample,
  • precipitation from the liquid, eg. calcium carbonate, aluminium hydroxide,
  • loss into the vapour phase,
  • absorption of carbon dioxide from the air, changing the pH value,
  • adsorption of metals and certain organic compounds on to the container's surface,
  • depolymerisation of polymerised products and vice versa.

These changes will be affected by the storage temperature, exposure to light, the nature of the container used and the time between sampling and analysis. In adverse conditions, changes can occur in just a few hours.

Fortunately, preservatives are available to prevent these changes. However, it must be borne in mind that methods of preservation are less effective with heavily contaminated samples than with those with light contamination.