PSA 50.042 Thermogram

The toxicity, biochemical behaviour and transport of mercury in the environment is highly dependant on its physio-chemical form.  Mercury in substrates such as ashes and soils is typically present as salts.  The differing solubilities of these salts affect the rate at which mercury is leached by the substrates.

Conventionally, determination of inorganic mercury speciation involves extensive sample preparation such as selective extractions and acid digestions.  An alternative method of speciating mercury in solid samples is thermal desorption with atomic fluorescence spectroscopy (TD-AFS).


The PSA 50.042 Thermogram consists of a two-stage tubular oven which is used, coupled to a PSA 10.025 Millennium Merlin. Small masses of sample are placed in a sample boat in the first part of the oven which is temperature controlled between ambient and 600oC.  As the oven temperature is increased the sample gradually undergoes thermal desorption, the different mercury salts evolving at characteristic temperatures according to their volatility

A stream argon (from the Millennium Merlin) continuously flows over the sample carrying the evolved gases through the second part of the oven which is maintained at 800oC to break down the evolved mercury compounds to elemental mercury. 


PSA SAMS Software can be used to control the Thermographic oven and record the Thermogram produced.  Alternatively, the temperature controller can be programmed manually and the Thermogram plotted on a chart recorder.


Typical Thermogram of barite

Preparation of a reference library of the temperatures at which different mercury salts are observed should enable the rapid identification of mercury species present in a solid sample.

The use of known concentration standards will enable a calibration strategy to be developed, allowing the quantitation of the mercury species.

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