UNITED STATES**ENVIRONMENT~PROTECTION** AGENCY RESEARCH TRIANGLE PARK. NC 2771 1

OFFICE OF AlA QUALITY PLANNING AND STANDARDS 

### MEMORANDUM;
SUBJECT: Minimum Detection Limit for EPA Method 5 

### FROM: Michael K. 

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# cAL Source Characterization Group B, (EMAD) MD-19
TO: Donald O. Wright Raritan Depot (MS220)

In response to your memorandum originally sent to the Agency in August 1994, the Emission Measurement Center (EMC) requested contractor assistance to determine the minimum particulate catch ofEPA Method 5 (40 CFR Part 60, Appendix A). You were concerned that our current guidance stating Method 5 samples should have a minimum catch of20 mg was too restrictive. You pointed out that some sources in yourregion might need to sample for 20 hours to collect 20 mg ofparticulate matter (PM). Finally, you asked that we review our guidance to see ifwe could reduce our recommended minimum catch.
The EMC's guidance on minimum catch is based on the minimum detection limit (MDL) ofthe sampling method. The MDL is the minimum concentration or amount ofan analyte that can be determined with 

### a specified degree ofconfidence to be different from zero. We have defined the minimum ortarget catch as a concentration or amount sufficiently larger than the MDL to ensure thatthe results are reliable and repeatable. For Method 5, the particulate matter (PM) catch is the product ofthe average PM concentration on amass per volume basis and the volume ofgas collected by the sample train. The tester can generally control the volume ofgas collected by increasing the sampling time orto a lesser extent by increasing the rate at which the sample is collected. Ifthe tester has a reasonable estimate ofthe PM concentration from the source, the tester can ensure that the target catch is collected by sampling the appropriate gas volume. However, ifthe source has a very low PM concentration in the stack, the volume ofgas sampled may need to be very large which leads to undesirably long sampling times. When determining compliance with an emission limit, our guidance has been that the tester does not always have to collect the target catch. Instead, in the past we have suggested that the tester sample enough stack gas, that ifthe source were exactly at the level ofthe emission standard, the

### 2 sample catch would equal the target catch. Thus, ifatthe end ofthe test the catch were smaller thanthe target, we could still conclude that the source is in compliance though we might not knowthe exact emission level. This volume ofgas becomes a targetvolume that canbe translated into a target samplingtime by assuming an average sampling rate. Becausethe MDL forms the basis for ourguidance ontarget samplingtimes, we began a systematic laboratory study to define whatis the MDL for Method 5. Attached is a copy ofthe fmal report ofthe "Minimum Detection Limit for Method 5" along withthe quality assurance (QA) report. This study design was based on guidelines publishedby the American Chemical Society's Committee onEnvironmental Improvement (ACSCEM) in Analytical Chemistry inDecember 1980. Although some scientists have criticized these guidelines, the EPAhas not agreed on an alternate policy for determining the MOL, and the EMC has continued to follow them 

### inthe interim. A copy ofthe article is attached.
The EMC decided thatthe practical limit ofquantitation (PLQ), which is the lowest level above which quantitative results may be obtained with an acceptable degree ofconfidence, was sufficiently above the MDL to be the target catch. The attached ACSCEM Guidelines explain the relationship betweenthe two terms. These guidelines formed the basis for the procedure described inMethod 301 for determining the PLQ. We used the dataprovided inthe attached report and followed the procedure specified in section 9.2 ofMethod 301 to determine the PLQ.
We obtained the PLQ by repeatedly analyzing a blank sample and then calculating the standard deviation (SO) ofthese results. The PLQ is equal to 10 times the standard deviation. We usedthe three sets ofTeflon baggie results (0-, 5-, and IO-mg particulate mattertests) and the blank sample trainresults from the reportto determine the standard deviation. Based onthe results ofa Dixon Test, [Dixon W.J. "Processing Data Outliers,"Biometrics 9 (1): 74-89 (1953)], we discarded the SD from the 10-mg PM test as an outlier. We calculated the average SD from the three remaining tests. Using the average SO, we calculated a PLQ of3 mg ofPM and an MOL ofl mg. Based onthese results, the EMC has concluded that for Method 5 the target catch must be no less than 3 mg. Those sample catches between 1mg and 3 mg are betweenthe detection limit andthe limit ofquantitation. Ifa tester uses the target catch to estimate a target sampling time that results in sample catches that are less than 3 mg, you should not automatically reject the results. Ifthe tester calculated the target samplingtime as described above by assuming that the source was atthe level ofthe emission limit, the results would still be valid for determining that the source was in compliance. Forpurposes otherthan determining compliance, results should be divided into two categories

- those that fall between 3 mg and 1mg and those that are below 1mg. A sample catch between 1 and 3 mg may be used for such purposes as calculating emissionrates with the understanding that the**r~sulting** emission rates can have a high degree of uncertainty. Results ofless than 1mg should notbe used for calculating emissionrates or pollutant concentrations.

### 3 Whencollecting small catches suchas 3 mg, bias becomes an important issue. Source testers mustuse extreme cautionto reach the PLQ of3 mgby assuring that samplingprobes are very clean (perhaps confmned by low blank weights) before use in the field. They should also use lowtare weight sample containers such as teflon baggies, and establish a well-controlled balance room to weigh the samples.
I hope thatthis information andthe attachments are helpful for guidance inreducing the duration ofparticulate sampling. Please call me at (919) 541-4921, ifyou need additional infonnation.
Attachments

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