VOC residuals, blanks and limits of detection using EPA Method-25 with sample recovery temperatures of 200{degrees}C and 500{degrees}C

Current protocol for recovery of volatile organic compounds (VOC) from Method-25 cryogenic traps call for heating the traps to 200{degrees} C while passing zero air through them. The effluent then passes through an oxidation catalyst where the VOC are converted to CO{sub 2}. When the CO{sub 2} concentration exiting the catalyst is <10 ppm, sample recovery is complete. This procedure leaves residual VOC in the trap due to the formation of high boiling compounds during the heating step. This material must be removed by heating the traps to higher temperatures. Quantitative measurement of these residuals and their effects on blank levels and the limit of detection of Method-25 shows that a higher recovery temperature is warranted. The need to clean the equipment at a higher temperature supplants the original intention of the 200{degrees} C recovery temperature of preserving the integrity of sampling equipment. A higher recovery temperature also dramatically decreases recovery times for many samples. Field blank levels for a 5L sample of {approximately}10 ppm as Carbon (ppmC) can be routinely achieved at sample recovery temperature of 500{degrees}C with little effect on the lifetime of sampling equipment. The limit of detection (LOD) for a 5L, sample volume recovered at 500{degrees}Cmore » was {approximately}20 ppmC, or {approximately}10 ppmC for a 10L sample volume.« less