NEMI Method Summary

Method Summary Information

Method Number: 375.2 Media: WATER
Revision: Revision 2.0, August 1993
Method Source: U.S. EPA National Exposure Research Laboratory (NERL) [formerly EMSL]
Analytes in this method
Subcategory: INORGANIC
Official Name: Sulfate (Colorimetric, Automated, Methylthymol Blue, AA II)
Descriptive Name Sulfate by Colorimetry
Source Info: U.S.EPA National Exposure Research Laboratory (NERL)
Microbiological and Chemical Exposure Assessment Research Division (MCEARD)
[formerly the Environmental Monitoring Systems Laboratory (EMSL), Cincinnati, OH]
26 West Martin Luther King Drive
Cincinnati, Ohio 45268-0001
Fax: 513-569-7757
email: DWmethods.help@epa.gov
Citation: Methods for the Determination of Inorganic Substances in Environmental Samples (EPA/600/R-93/100)
312675 Byte file
Brief Method
Summary:
 A sample is first passed through a sodium form cation-exchange column to remove multivalent metal ions. The sample containing sulfate is then reacted with an alcohol solution of barium chloride and methylthymol blue (MTB) at an acidic pH to form barium sulfate. The combined solution is raised to a basic pH so that excess barium reacts with MTB. The uncomplexed MTB color is gray; if it is all chelated with barium, the color is blue. Initially, the barium and MTB are equimolar and equivalent to 300-mg SO4/L; thus the amount of uncomplexed MTB is equal to the sulfate present. The amount of sulfate in the sample is measured by measuring the absorbance of uncomplexed MTB using a spectrophotometer.
Scope And
Application:
 This method determines sulfate in drinking, ground and surface water; domestic and industrial wastes.
Applicable
Conc Range:
 3 - 300 mg/L and 0.5 - 30 mg/L (with minor modification)
Interferences:

(A) Ion exchange column breakdown: Run sulfate/Ca+2standard to ensure proper column operation.

(B) Turbidity: Filter or centrifuge turbid samples.

(C) Contamination: Reagents or glassware can be contaminated.
QC Requirements:

The minimum recommended quality control requirements include an initial demonstration of laboratory capability (determining the linear calibration range and method detection limit, and analyzing a quality control sample; LCR and MDL, and QCS), and the periodic analysis of a laboratory reagent blank.

Sample Handling:

Samples should be collected in thoroughly clean plastic or glass bottles and should be of sufficient volume to ensure a representative sample.

Samples must be preserved with H2SO4 to a pH < 2 and cooled to 4oC at the time of collection.
Max Holding Time:
 28 days (MCAWW, Table 1).
 
Relative Cost: Less than $50
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