A New Audit Method for EPA Reference Method 6

Abstract

A simple, inexpensive, and accurate method for evaluating and/or auditing sampling and analytical phases of the EPA Source Reference Method 6 was developed. The method uses a known amount of a chemical compound in the form of a tablet or pill (or placed in a capsule) to generate sulfur dioxide quantitatively by reaction with an acid. The reaction takes place in a compact glass impinger system that can be taken to the field. The S0₂ generated in test runs was collected and analyzed using the Method 6 procedure. The SO₂ generation was quantitative and recoveries were found to be 94 ± 5 %. The time to complete the reaction was less than 15 min at a flow rate of 1 L/min, but the recommended sampling time was 45 min. The tablets prepared gravimetrically were found to be stable over a sixmonth period. The interlaboratory results obtained showed close agreement with the expected concentrations based on calculations from the stoichiometric reaction. The estimates of repeatability (or within-laboratory precision) were ±5.0 mg 95% of the time for the two concentration levels tested. The reproducibility (or betweenlaboratory precision estimate) was within ±5.9 mg at the low range and ±23.8 mg at the high range about 95% of the time. The maximum bias observed for the method was 0.5%.