Method 6A

Determination of Sulfur Dioxide and Carbon Dioxide From Fossil Fuel Combustion Sources

This method is used for the determination of gaseous sulfur dioxide, carbon dioxide and moisture content from fossil fuel combustion sources. A gas sample is extracted from the stack and collected using a midget impinger sampling train. Sulfur dioxide (SO2) and sulfur trioxide (SO3), including these fractions in any sulfuric acid mist, are separated in the train.  Sulfur dioxide is then measured by the barium-thorin titration method.  Carbon dioxide (CO2) and moisture content are determined gravimetrically.

A modified Method 6 train consisting of a heated probe, midget bubbler, a series of midget impingers, another midget bubbler and a CO2 absorber is used for collection.  A midget bubbler is filled with 15mL of 80% isopropanol.  Two midget impingers are filled with 15mL of 3% hydrogen peroxide (H2O2) followed by another bubbler filled with 25mL of Drierite.  TheCO2 aborber follows and is filled with Ascarite II.  A second smaller CO2  absorber can be used to determine breakthrough.  The second desorber is placed downstream of the first absorber.  Ascarite II turns white when CO2  is absorbed.  If the Ascarite II in the second CO2  absorber turns white, there is breakthrough.

All impingers and the CO2 absorber are weighed to determine the moisture content.  Once the weighing has been completed, the contents of midget bubblers and CO2 absorber can be discarded.  The contents of the midget impingers are combined in a polyethylene bottle.  The impingers and connecting glassware are rinsed with deionzied water and the rinse is combined with the impinger contents.

An aliquot is taken from the sample, a thorin indicator added and the sample is titrated with a barium standard.  A separate aliquot is taken and the titration repeated.  The average value is reported and the replicates must agree within 1% or 0.2mL whichever is greater. 

If the data are to be used for compliance with source emission regulations then the method requires the analysis of an audit sample along with the collected field samples.  In order for the audit to pass, the method cites an agreement within 5% from the value determined in the analysis to the accepted true concentration of the audit sample.

(EPA 40CFR Part 60 Appendix A)


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Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:   None specified in method.
Preservatives:   None specified in method.
Required Preps:   None specified in method.
Collection Method:   Method 6 train following Method 6A procedures.
Analytical Methodology:   Barium-thorium Titration
Documentation:   M6A

Analyte List*

Analyte Formula CAS Number Detection Limit
Sulfur dioxide

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.