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 the Agency in August 1994, the 

Emission Measurement Center (EMC) requested contractor assistance to 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 a minimum catch of 20 mg was too 

restrictive. You pointed out that some sources in your region might need to sample for 20 hours 

to collect 20 mg of particulate matter (PM). Finally, you asked that we review our guidance to 

see if we could reduce our recommended minimum catch. 

The EMC’s guidance on minimum catch is based on 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 a specified degree of confidence to be different from zero. 

We have defined the minimum or target catch as a concentration or amount sufficiently larger 

than the MDL to ensure that the results are reliable and repeatable. For Method 5, the 

particulate matter (PM) catch is the product of the average PM concentration on a mass per 

volume basis and the volume of gas collected by the sample train. The tester can generally 

control the volume of gas collected by increasing the sampling time or to a lesser extent by 

increasing the rate at which the sample is collected. If the tester has a reasonable estimate of the 

PM concentration from the source, the tester can ensure that the target catch is collected by 

sampling the appropriate gas volume. 

However, if the source has a very low PM concentration in the stack, the volume of gas 

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 if the source were exactly at the level of the emission standard, the 

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sample catch would equal the target catch. Thus, if at the 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 gas becomes a target volume that can be 

translated into a target sampling time by assuming an average sampling rate. Because the MDL 

forms the basis for our guidance on target sampling times, we began a systematic laboratory 

study to define what is the MDL for Method 5. Attached is a copy of the final report of the 

“Minimum Detection Limit for Method 5” along with the quality assurance (QA) report. This 

study design was based on 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, and the 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 

above which quantitative results may be obtained with an acceptable degree of confidence, was 

sufliciently above the MDL to be the target catch. The attached ACSCEM Guidelines explain 

the relationship between the two terms. These guidelines formed the basis for the procedure 

described in Method 301 for determining the PLQ. We used the data provided in the attached 

report and followed the procedure specified in section 9.2 of Method 301 to determine the PLQ. 

We obtained the PLQ by repeatedly analyzing a blank sample and then calculating the 

standard deviation (SD) of these results. The PLQ is equal to 10 times the standard deviation. 

We used the three sets of Teflon baggie results (0-, 5-, and lo-mg particulate matter tests) and the 

blank sample train results from the report to determine the standard deviation. Based on the 

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 

the three remaining tests. Using the average SD, we calculated a PLQ of 3 mg of PM and an 

MDL of 1 mg. 

Based on these results, the EMC has concluded that for Method 5 the target catch must be 

no less than 3 mg. Those sample catches between 1 mg and 3 mg are between the detection limit 

and the limit of quantitation. If a 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. If the tester calculated the target sampling time as described above by assuming that the 

source was at the level of the emission limit, the results would still be valid for determining that 

the source was in compliance. For purposes other than determining compliance, results should 

be divided into two categories - those that fall between 3 mg and 1 mg and those that are below 

1 mg. A sample catch between 1 and 3 mg may be used for such purposes as calculating 

emission rates with the understanding that the resulting emission rates can have a high degree of 

uncertainty. Results of less than 1 mg should not be used for calculating emission rates or 

pollutant concentrations. 

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When collecting small catches such as 3 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 as teflon baggies, and establish a well-controlled 

balance room to weigh the samples. 

I hope that this information and the attachments are helpful for guidance in reducing the 

duration of particulate sampling. Please call me at (9 19) 54 I-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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