Encyclopedia of Environmental Science and Engineering, Volume I and II

1122 STACK SAMPLING

traps in series. Any condensate present is collected between

the two resin traps. The first trap contains approximately

1.6 grams of 2,6-diphenylene oxide polymer (Tenax). The

backup trap contains approximately 1 gram each of Tenax

and carbon. Both traps are cleaned by purging with a nitro-

gen while heating the traps to 190ºC. The method provides

detailed instruction for the preparation of the sorbent tubes.

The gases are dried before they are pumped by a vacuum

pump through a dry gas meter.

Because of the relatively short time that each pair of

tubes may collect samples, and the need to sample over at

least an hour, a total of three pairs of tubes must be analyzed

for each run. To account for the possibility of tube break-

age during transport and analysis, between 4 and 6 pairs are

actually collected. Each tube is analyzed by first heating the

trap to desorb the compounds that are then collected on a

smaller analytical trap. This tube is heated quickly and the

compounds separated by gas chromatography and quanti-

fied with a suitable detector. The back-up traps are analyzed

separately. When the traps are desorbed, the second, or

back-up, trap should contain less than 30% of each organic

compound. If this is not the case, there is a possibility of sig-

nificant breakthrough of that compound through the traps.

The condensate should be analyzed to show that there are no

organic compounds present. To increase the detection limit,

all three of each type of tube can be analyzed together.

This method requires extensive quality assurance and

quality control measures to insure that valid data is produced.

The majority of problems with this technique are usually from

contamination of the sorbent traps in the field or laboratory.

The analysis of audit gas provided by the Quality Assurance

Division at Research Triangle Park, NC is required in the

Method. This method should be performed only by personnel

familiar with the sampling method and the gas chromatography

necessary for the analysis.

Test Methods 204 et al.

EPA has published a number of Test Methods, Protocols,

Procedures, and Regulations all aimed at determining the

effectiveness of a control device to capture potential emis-

sions of volatile organic compounds (VOCs). As a prelude

to testing, most of the Procedures require the source to

construct and verify a total enclosure, either permanent or

temporary. Method 204 and Methods 204 A through F (pub-

lished in Appendix M of 40 CFR Part 51) are to be used for

measuring the VOC content in various process and emission

streams, and for verifying the total enclosure. Then, addi-

tional Procedures from Part 52 are used to determine the

actual Capture Efficiency.

DONALD G. WRIGHT

MARCUS E. KANTZ

U.S. Environmental Protection Agency

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