This method describes the continuous sampling of mercury in combustion flue gas streams using sorbent traps. Analysis of the samples is performed using cold vapor atomic fluorescence (CVAF) or cold vapor atomic absorption (CVAA). Total vapor phase mercury is reported representing the sum of elemental and oxidized forms of mercury. The method is good for mercury found in the range of 0.3 ug/dncm to 100 ug/dncm.
Samples are collected using a sorbent tube attached to a probe which is inserted directly into the stack. The probe is unheated if the stack temperature is 200-375°F. If the stack temperature is <200°F, the trap must be heated to at least 200°F or higher to avoid liquid condensation in the trap. If the stack temperature is >375°F, a larger sorbent trap must be used. After sampling the trap is removed from the probe and the ends capped for shipment to the laboratory. Note that all handling of the trap in the field should be with power-free low level mercury gloves that have not touched any other surface.
The sorbent traps are specially prepared following procedures to ensure no mercury contamination. The method requires <5ng per trap of mercury for a blank traps.
Each sorbent trap has a front half and back half section. There are now some traps made containing three separate sections. The method specifies small and large traps each containing two sections. The use of the small or large traps is dependent upon the sampling times and expected concentrations of mercury in the stack. The method specifies that the front and back half sections be analyzed separately to check for breakthrough. The breakthrough requirement for the back half is <2% of front half or <5/ng per trap.
The samples are prepared with a hot-acid leach of 70:30 nitric acid to sulfuric acid, diluted and then analyzed. Each sample must be analyzed in duplicate with every 10th analysis measured in triplicate. The results of the analysis must agree within 10%.
NOTE: This method has been updated and replaced with US-EPA Appendix K (40CFR, Appendix K) and Method 30B.
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| Hold Times, Preservatives, Preps, Collection, Analytical & Documentation | |
|---|---|
| Holding Time: | None specified in method. |
| Preservatives: | None specified in method. |
| Required Preps: | Specially prepared sorbent tubes. |
| Collection Method: | Probe and sorbent trap following Method 324 procedures. |
| Analytical Methodology: | CVAF or CVAA |
| Documentation: | |
| Analyte | Formula | CAS Number | Detection Limit | |
|---|---|---|---|---|
| Mercury | Hg |
7439-97-6 |
30 |
μg/dncm |
* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.