UNITED STATES ENVIRONMENT&PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711

OFFICE OF AIR QUALITY PLANNING AND STANDARDS MEMORANDUM;
SUBJECT: Minimum Detection Limit for EPA Method 5

. FROM: Michael K. Ciolek

Source Characterization droup B, (EMAD) MD-19
TO: Donald G. Wright

Raritan Depot (MS220)

In response to your memorandum originally sent to theAgency in August 1994,the Emission Measurement Center (EMC) requested contractor assistanceto determine the minimum particulate catch of EPA Method 5 (40 CFR Part 60, Appendix A). You were concerned that our current guidance stating Method 5 samples should have aminimum catch of 20 mg was too restrictive. You pointed out that some sources in your region might needto sample for 20 hours to collect 20 mg of particulate matter (PM). Finally, you askedthat we review our guidance to seeif we could reduce our recommended minimum catch.
The EMC’s guidance on minimum catch is basedon the minimum detection limit (MDL) of the sampling method. The MDL is the minimum concentration or amount of an analyte that can be determined with aspecified degreeof confidence to be different from zero. We have defined the minimum or target catch asa concentration or amount sufficiently larger than the MDL to ensurethat the results are reliable and repeatable. For Method 5, the particulate matter (PM) catch isthe product of the average PM concentration on amass per volume basis andthevolume of gascollected by the sample train. The tester can generally control thevolume of gascollected by increasing the sampling time or to a lesser extent by increasing the rate atwhich the sample is collected. If the tester has a reasonable estimate of the PM concentration from the source,the tester can ensurethat thetarget catch is collected by sampling the appropriate gasvolume. However, if the source has avery low PM concentration in the stack, thevolume of gas sampled may needto bevery large which leadsto undesirably long sampling times. When determining compliance with an emission limit, our guidance has beenthat the tester doesnot always haveto collect the target catch. Instead, in the past we have suggestedthat the tester sample enough stack gas,that if the source were exactly atthe level of the emission standard,the

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sample catch would equal the target catch. Thus, if atthe end of the test the catch were smaller than the target, we could still conclude that the source is in compliance though we might not know the exact emission level. This volume of gasbecomes atarget volume that can be translated into atarget sampling time by assuming an averagesampling rate. Becausethe MDL forms the basis for our guidance on target sampling times, we began asystematic laboratory study to define what is the MDL for Method 5. Attached is acopy of the final report of the “Minimum Detection Limit for Method 5” along with the quality assurance(QA) report. This study design was basedon guidelines published by the American Chemical Society’s Committee on Environmental Improvement (ACSCEM) in Analvtical Chemistrv in December 1980. Although some scientists have criticized these guidelines, the EPA has not agreed on an alternate policy for determining the MDL, andthe EMC has continued to follow them in the interim. A copy of the article is attached.
The EMC decided that the practical limit of quantitation (PLQ), which is the lowest level abovewhich quantitative results may be obtained with an acceptable degreeof confidence, was sufliciently abovethe MDL to bethe target catch. The attached ACSCEM Guidelines explain the relationship between thetwo terms. These guidelines formed the basisfor the procedure described in Method 301 for determining the PLQ. We usedthe data provided in the attached report andfollowed the procedure specified in section 9.2 of Method 301 to determine the PLQ.
We obtained the PLQ by repeatedly analyzing ablank sample andthen calculating the standard deviation (SD) of these results. The PLQ is equal to 10times the standard deviation. We usedthethree setsof Teflon baggie results (0-, 5-, and lo-mg particulate matter tests) andthe blank sample train results from the report to determine the standard deviation. Based onthe results of a Dixon Test, [Dixon W.J. “Processing Data Outliers,” Biometrics 9 (1): 74-89 (1953)], we discarded the SD from the 1 0-mg PM test as an outlier. We calculated the average SD from thethree remaining tests. Using the average SD, we calculated a PLQ of 3 mg of PM and an MDL of 1mg.
Based onthese results, the EMC has concluded that for Method 5the target catch must be no lessthan 3 mg. Those sample catches between 1mg and 3 mg arebetween the detection limit andthe limit of quantitation. If atester usesthe target catch to estimate atarget sampling time that results in sample catchesthat are lessthan 3 mg, you should not automatically reject the results. If thetester calculated the target sampling time asdescribed above by assuming that the sourcewas atthe level of the emission limit, the results would still be valid for determining that the sourcewas in compliance. For purposes other than determining compliance, results should bedivided into two categories - thosethat fall between 3 mg and 1mg andthose that arebelow 1mg. A sample catch between 1and 3 mg may beusedfor such purposes ascalculating emission rateswith the understanding that the resulting emission rates can have ahigh degreeof uncertainty. Results of lessthan 1mg should not be usedfor calculating emission ratesor pollutant concentrations.

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When collecting small catches such as3 mg, bias becomes an important issue. Source testers must use extreme caution to reach the PLQ of 3 mg by assuring that sampling probes are very clean (perhaps confirmed by low blank weights) before use in the field. They should also use low tare weight sample containers such asteflon baggies, and establish awell-controlled balance room to weigh the samples.
I hope that this information andthe attachments arehelpful for guidance in reducing the duration of particulate sampling. Please call me at (919) 54I-492 1,if you need additional information.
Attachments

cc: Roy Huntley (MD- 14) Bill Lamason (MD- 19) Gary McAlister (MD-l 9) Conniesue Oldham (MD-19) Robin Segall (MD-19) Roger Shigehara (Entropy) Peter Westlin (MD- 19)

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