ASTM-D4148 Historical Revision Information
Standard Test Method for Analysis of Phytoplankton in Surface Water by the Sedgwick-Rafter Method

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Standard Test Method for Analysis of Phytoplankton in Surface Water by the Sedgwick-Rafter Method (Withdrawn 2020)


1.1 This test method covers determining the density and taxonomic classification of phytoplankton. It is applicable both to relatively sparse or dense phytoplankton concentrations, provided the suspended-sediment concentration is low. The Sedgwick Rafter (S-R) method requires less costly apparatus than does the inverted microscope method but gives less accurate results. The inherent inaccuracy in the Sedgwick-Rafter method is due to the design of the counting chamber and cannot be circumvented by a different choice of optics. For this reason, the S-R method is limited to the use of objective lenses having a working distance of approximately 1.6 mm or more. With 10X oculars the maximum overall magnification is approximately 250X. High concentrations of suspended sediment can obscure the algal cells, and thus cause interference.

1.2 This test method is applicable to both freshwater and marine samples.

1.3 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. For specific precautionary information see Section 8.


Microscopic examination-water; Phytoplankton; Sampling-phytoplankton; Sedgwick-Rafter method; analysis of phytoplankton in surface water, by Sedgwick-Rafter method

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Document Number


Revision Level

1982 R98 EDITION



Modification Type


Publication Date

June 25, 1982

Document Type

Test Method

Page Count

3 pages

Committee Number