Validation of an Audit Material for EPA Method 6B

Abstract

A simple audit material for EPA Method 6B was developed in a compressed gas cylinder and validated at three different laboratories. The audit mixture of CO₂ (10 percent) and SO₂ (250 ppm) in a balance gas of nitrogen prepared in aluminum cylinders was found to be stable over a 1-year period. The interlaboratory results obtained for the audit mixture using EPA Method 6B procedures showed reasonable agreement (SO₂ and CO₂ are within 7.5 percent and 5.3 percent, respectively) with EPA-measured concentrations except in one case, which was probably due to some contamination in the laboratory. A second audit material which uses chemical reactions to generate SO₂ and CO₂ was also developed. However, this approach was discontinued because it was difficult to simultaneously generate ppm levels of SO₂ and percent levels of CO₂ by chemical reactions in the field.