|
|
Home >
Background >
Methods of Low Level Atmospheric Measuremnets
|
|
|
|
|
|
Methods Of Low Level Atmospheric Measurement
Total Gaseous Mercury
Most analytical techniques do not differentiate between mercury forms and yield a total mercury concentration. Over the years, many methods have been developed attempting to measure the extremely low levels of mercury typically found in the atmosphere. The fundamental difficulty lies in that mercury is present in concentrations that may be many orders of magnitude less than potential interfering compounds.
These methods appeared to produce satisfactory results in most cases when interferences were not present. However, it was not always obvious when a particular method was working and when it was giving anomalously high or low results.
All of the low level methods depend on pre-concentration of the mercury onto an absorbent cartridge of some type, generally for periods of 6 or 24 hours. This is usually followed by subsequent analysis in a laboratory. Adsorbents used have included hopcolite, silver, iodized carbon, gold coated sand, gold coated quartz wool or gold coated quartz beads.
Detection was formerly performed using cold vapor atomic absorption spectrophotometry (CVAAS), however, cold vapor atomic fluorescence spectrophotometry (CVAFS) is now the preferred method due to better sensitivity, specificity and linearity.
Tekran has standardized on CVAFS detection with pure gold preconcentration. This method is sensitive, immune to false positive readings and does not suffer from negative interferences.
Atmospheric Speciation
The determination of species of mercury in the atmosphere is considerably more difficult than the measurement of total mercury. Speciation methods must extract the signal due to RGM or HgP while ignoring the much greater elemental component. RGM compounds are extremely "sticky" and do not travel well through instrument components.
Tekran has developed a preconcentration and thermal regeneration technique that allows unattended, automated sampling of the three classes of mercury. (Model 1130 and Model 1135.)
|
|
|
|