EPA Method 18 - Direct / Dilution Interface
- The sample is withdrawn directly from the source through heated line to the GC
- Analysis is semi-continuous with a snapshot every 5-20 minutes
- Method 18 requires a minimum of five injection per test run
- Sample degradation issues are minimized by direct injection into the GC
- Direct injection is an excellent tool for tracking batch processes (unless the process changes can occur faster than the snapshot injection times)
- EPA Method 18 is suitable for most organic compounds
- Unsuitable compounds are those that:
- Are polymeric (high molecular weight);
- Can polymerize before analysis; and/or
- Have very low vapor pressures at stack or instrument conditions.
- The lower range of this procedure is determined by the sampling system; adsorbents may be used to concentrate the sample, thus lowering the limit of detection below the 1 ppm level typically achievable with direct interface sampling.
- The upper limit is governed by teh GC detector saturation or column overloading. The upper range can be extended by dilution interface sampling.
- Sample is withdrawn from the source and delivered continuously to the GC (similar to EPA Method 25A). A preferred sampling rate would yield a response time of less than one minute.
- All heated elements should be set to ~250oF;
- A slip-stream of the sample is drawn through a gas sampling valve on the instrument;
- An injection is performed by rotating the valve;
- Each injection will typically require 5-20 minutes to perform the analysis.
- A recovery study must be performed following sampling (similar to sample system bias);
- Performed by introducing sample to the probe tip and sampling similar to stack gases;
- Recovery is acceptable if bias is within +10% of the at-instrument value.
- Analysis results are typically not corrected for this recovery study results
- Short lengths of unheated lines can cause sample loss through condensation (e.g. 4" of teflon line). All sample delivery lines should be heated.
- No shipping issues - samples analyzed on-site
- Fuel gas analyses (Btu Content);
- Emissions of almost any VOC from process vents;
- Method can (and probably should) be coupled directly with THC (EPA Method 25A) Continuous Measurements.
- Destruction and Removal Efficiency of individual Analytes
Simultaneously Measure at Inlet and Outlet of a control device.
- Yes we are, please contact us if you are interested!
- New Jersey