This method describes procedures for the collection and determination of total mercury in natural gas streams. Mercury from gaseous streams is absorbed and preconcentrated onto a gold-coated, fused silica sand trap. The analyte is thermally desorbed from the tube and analyzed using atomic fluorescence spectroscopy (AFS). This method is capable of reporting mercury down to 0.001 ug/m3.
The sampling apparatus is described within the method and consists of a probe, regulator and dry flow meter. Note that stainless steel tubing and connections are required per the method. The recommended sampling parameters are 100-200 mL/min. flow rate for 15-30 minutes. It is also specified to collect two traps per sampling location. These traps are in series in the sampling train and are then analyzed separately to check for breakthrough.
The analytical portion of this method is an update of ASTM D-5954 which used atomic absorption spectroscopy to analyze the sample. AFS allows for lower detection limits and longer sampling times which helps to lessen interferences caused by hydrogen sulfide (H2S). Note that other labs have also used CV-AFS (cold vapor atomic fluorescence spectrocopy) to achieve even lower limits of detection.
The method calls for use of a gold-coated fused silica sand trap, however, other traps made of gold-coated quartz or similar materials can be used to obtain similar results.
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| Hold Times, Preservatives, Preps, Collection, Analytical & Documentation | |
|---|---|
| Holding Time: | None specified in method. |
| Preservatives: | None specified in method. |
| Required Preps: | Gold-coated fused silica sand trap |
| Collection Method: | ASTM D-6350 sampling train |
| Analytical Methodology: | Thermal desportion AFS (atomic fluorescence spectroscopy) |
| Documentation: | |
| Analyte | Formula | CAS Number | Detection Limit | |
|---|---|---|---|---|
| Mercury | Hg |
7439-97-6 |
0.001 |
ug/m3 |
* 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.