OC/EC thermo-optical analysis is a method of reference to determine concentrations of particulate organic carbon (OC) and elemental carbon (EC) collected on quartz fibre filters.
Once the system is closed and pressurised, the oven is purged with helium to remove ambient air. A stepped temperature ramp increases the oven temperature to 650°C, thermally desorbing the organic compounds. The OC fraction is oxidised to CO2 gas into a manganese dioxide (MnO2) oxidising oven, CO2 is measured using non-dispersive infrared (NDIR). The oven temperature is then reduced to 500 °C. At this stage of the analysis, all the carbon measured represents the original OC compounds on the filter sample. What remains on the filter is original EC as well as EC produced from thermal pyrolysis (charring) of organic compounds such as high molecular weight OC’s and polymeric materials, especially from natural products. The carrier gas is then replaced by a mixture of helium and 2% oxygen. A second temperature ramp is initiated to oxidise remaining EC from the filter that will be detected by NDIR. The measured total carbon (TC) of the sample is the sum of organic and elemental carbon ( OC+EC=TC).
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