EPA Method 425.1

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EPA Method 425.1:
Surfactants by Colorimetry. Official Name: Methylene Blue Active Substances (MBAS) (Colorimetric)

Summary:
Methylene blue reacts with anionic-type surface active materials to form a blue colored sample. The salt is extracted with chloroform and intensity of the color in the extract is proportional to the concentration of methylene blue active substances (surfactants).

Scope:
This method determines methylene blue active substances (surfactants) in drinking water, surface water; domestic and industrial wastes. The method is not applicable to saline waters.

Citation:
Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)

Interferences:
Compounds: Many compounds other than surfactants can react with methylene blue, including organically bound sulfates, sulfonates, carboxylates, phosphates, phenols, cyanates, thiocyanates, and some inorganic ion such as nitrates and chlorides. However, the occurrence of these compounds is usually rare (with the exception of chlorides).

QC Requirements:
None.

Maximum Holding Time:
48 Hours (MCAWW, Table 1).

Media:
WATER

Subcategory:
Organic

Concentration:
0.025 to 100 mg/L linear alkyl sulfonate.

Sample Prep:
None.

Precision:
Precision and accuracy values were determined using analyses of fortified distilled water by 110 analysts. Additional data are available in the method.

Detection:
None.

Revision Number:
Issued 1971

Test Description:
Surfacants Methylene

Report Number:
600/4-79-020

Instrument used for this test:
UV-VIS