USGS


Water Resources--Office of Water Quality

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smallbeakersNational Field Manual


FILTERED SAMPLES   5.2

By D.B. Radtke, A.J. Horowitz, and M.W. Sandstrom

Filtration is the physical process used to separate the particulate and aqueous fractions of a water sample. Samples are filtered for several purposes; for example, to remove microorganisms in order to help preserve ambient analyte concentrations, to remove suspended materials that interfere with specified analytical procedures, and to determine chemical speciation and fractionation of trace elements for geochemical studies.

Study objectives and the analytes targeted for study dictate the filtration method and equipment to be used. Ambient concentrations of filtered analytes typically can be near the limit of detection; therefore, field personnel must pay strict attention to possible sources of contamination from sampling and processing equipment, construction material of the chamber frame and of the filtration equipment, and the way the equipment is handled. (Equipment and supplies used to filter water samples are described in detail in NFM 2.)

Check the composition and pore size of the filter medium and the effective filtration area of the filter; these can affect the quality and accuracy of the data and can compromise data-quality requirements.
To minimize airborne contamination,
  -- Filter samples within a processing chamber.
  -- Add chemical treatments to samples within a separate preservation chamber.

 

Filter samples during or immediately after sample collection.

 

 

 


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