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Landfill gas - Total non-methane organics & NItrogen An evacuated stainless-steel canister is used to collect the sample. A sampling probe is punched into the landfill cap and a canister is attached to a sample line extending from the probe. The canister vacuum is exposed to the sample line to draw in gases emanating from the landfill. The canister is pressurized with helium in the laboratory prior to analysis.
The canister is attached to the analytical instrument and a sample loop is filled with the contents of the sample and then swept into a GC equipped with a flame ionization detector (FID) and thermal conductivity detector (TCD). Using a series of valves and columns, methane and carbon dioxide are allowed to elute from the column whereupon the remaining sample is diverted to another column to be detected by the FID as one chromatographic peak. Simultaneously, a portion of the sample is detected by the TCD for the quantification of nitrogen and oxygen. The concentration of the nitrogen found in the canister can determine if any leaks occurred during sample collection.
EPA Methods 25C and 3C dictate that the system be calibrated against propane, reported as parts per million as carbon, and then corrected for nitrogen and moisture. The quality control of EPA 25C includes triplicate analysis of each level of the calibration curve, triplicate analysis of the samples, analysis of a method blank, and analysis of a daily standard. The precision of EPA 3C duplicate analyses, that is both the QC samples and air samples, must be 5% or less. The Tables above list the routine analytes reported for these methods. |
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