School of Earth and Environment

Carbon and sulphur analysis

Background

The LECO is designed to determine the carbon and sulphur content of materials. It has a tube furnace kept at a constant 1350oC with a pure oxygen atmosphere into which you place your sample. At this temperature the sample combusts releasing CO2 and SO2. The gases flow through two anhydrone tubes to remove water and a separate halogen trap.

They then go through the IR detection cell to measure the concentration of CO2 and SO2. The instrument converts these measurements into percentage (or ppm) values taking into account the sample mass and calibration.

Instrument capabilities

The instrument is a LECO SC-144DR Dual Range Sulfur and Carbon Analyzer.

During analysis, a sample of approximately 300mg is weighed into a combustion boat and positioned inside the LECO furnace, which is set at 1350°C and flooded with pure oxygen. This causes the sample to combust, releasing carbon and sulphur as CO2 and SO2 gases

After leaving the combustion system the sample gases flow through two anhydrone tubes in order to remove moisture, into a flow controller set to regulate flow to 3.5 l/min, and then into the infrared detection cell. Here individual Carbon and Sulphur infrared detection cells respectively measure CO2 and SO2 concentrations. The software converts these measurementsto a percentage/ppm value utilising a pre-existing equation that corrects for sample weight, calibrations and known moisture value.

The LECO interface is supported by Windows based operating software loaded and run on a PC.

Practical considerations

Only 200-300mg of sample are required for this technique. Samples must be weighed out to 0.1mg precision and are normally carried out in duplicate. Samples and standards should be weighed out so mass of sample and standard used should be similar (±10 mg).

 Standards used are chosen to give a range of carbon and sulphur contents. Common standards include:

  • Low C soil
  • High C soil
  • ZnSO4
  • CaCO3
  • Coal

Samples should also be washed clean of any chlorine (e.g. from hydrochloric acid) to avoid releasing Cl gas into the atmosphere. There is a halogen trap to catch any Cl which is released accidentally.

 

Written by Luke Faggetter (23/06/2014)

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