|Text of Test Method 6C - SO2 - Instrumental - Posting Date: 11/6/2008
|Electronic Reporting Tool
FREQUENTLY ASKED QUESTIONS (FAQS) for Method 6C
The current version of Method 6C does not address the quenching effects that may occur with fluorescence analyzers.
Older versions of the method required that calibration gases contain oxygen and carbon dioxide within 1 percent
of the concentrations of the source if other preventive measures are not used. Is there still a concern for this
type of interference with fluorescence analyzers?
Fluorescence analyzers should still be evaluated for quenching effects unless a dilution system and ambient-level
analyzer is used. This evaluation and verification should take place in the interference test. The requirement
in older versions of Method 6C to prepare the calibration gas to contain within 1 percent of the absolute oxygen
and carbon dioxide content of the measured gas were dropped in a recent update of the instrumental test methods
since other means of handling the interference were available (such as preparing the SO2 gas in air and using vendor
nomographs or by using a gas dilution system and ambient level analyzer). However, in cases where these or other
acceptable techniques are not used, the tester should still match the calibration gas oxygen and carbon dioxide
concentrations within 1 percent of the source. This requirement will be added back to Method 6C in a future rulemaking
to add clarity.
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