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Method 6C - SO2 - Instrumental

Text of Test Method 6C - SO2 - Instrumental PDF file
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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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