EPA Method 206.4

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EPA Method 206.4:
Arsenic by Spectrophotometry. Official Name: Arsenic (Spectrophotometric-SDDC)

Arsenic in the sample is reduced to arsine (arsenic trihydride) in acid solution in a hydrogen generator. The arsine is passed through a scrubber to remove sulfide and is absorbed in a solution of silver diethyldithiocarbamate dissolved in pyridine. The absorbance of the red complex that forms is proportional to arsenic concentration and is measured with a spectrophotometer.

This method determines inorganic arsenic in drinking water and most fresh and saline waters in the absence of high concentrations of chromium, cobalt, copper, mercury, molybdenum, nickel, and silver. Industrial wastes may be analyzed after digestion by EPA Method 206.5.

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

(A) Odor: If pyridine odor is objectionable, 1-Ephedrine in chloroform can be use as a solvent for silver diethyldithiocarbamate.(B) Nitric acid: Nitric acid can produce a negative interference. Use sulfuric acid as a preservative if only inorganic arsenic is being measured.For additional interferences see EPA Methods 200.0 and 206.5.

QC Requirements:
Spike industrial waste samples with a known amount of arsenic to establish adequate recovery. QC requirements for drinking water procedures are provided in method 200.0.

Maximum Holding Time:
6 months (MCAWW, Table 1).



Above 10 ug/L.

Sample Prep:
200.0, 206.5

Precision and accuracy values were determined using data from analyses of synthetic samples containing arsenic (and other metals) at 46 laboratories. See Standard Method 404A, 14th Edition (1975) for additional information.


Revision Number:
Issued 1971; Editorial Revision 1974