Analysis of Elemental and Organic Carbon (EC/OC) by Thermal-Optical Analysis (TOA) (CAT#: STEM-EA-0128-ZJF)

Introduction

Thermal-Optical Analysis (TOA) is a quantitative analysis technique for measuring elemental and organic carbon (EC/OC) in a sample. Utilizing the industry-leading OC-EC analyzer, we provide EC/OC analysis based on the analysis of bulk samples and aerosol particles collected on quartz-fiber filters. The precision of the Thermal-Optical method of analysis, measured as a relative standard deviation, falls into the 4-6% range for samples that are in the concentration ranges of 5 to 400ug/cm2 for OC, and 1 to 15ug/cm2 for EC. To ensure that the accuracy doesn’t fall outside of the ideal values, reference tests can be performed using known concentrations of carbon-based materials (such as sucrose). The lower detection limit of this method is on the order of 0.2ug/cm2 for both OC and EC, so if lower detection limits are needed for a specific sample, then trace element analysis methods are required.

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Principle Applications Procedure Materials Notes Related Products

Principle

Thermal-optical analysis relies on the analysis of optical behavior of carbon in a particulate sample which is typically carried out by carefully and continuously monitoring the optical absorbance of the sample. In the OC-EC Analyzer, samples are thermally desorbed from the filter medium under an inert helium atmosphere followed by an oxidizing atmosphere using carefully controlled heating ramps. A flame ionization detector (FID) is used to monitor the analysis. The proven low dead volume carrier gas control system and proprietary quartz oven design provide high sensitivity with ultra low carbon background and no oxygen contamination.

Applications

Ambient and occupational air quality, aerosol and climate research, air pollution source apportionment, standard method for organic and elemental carbon

Procedure

1. In a completely oxygen-free helium atmosphere, the carbon sample is heated in different incremental steps to remove the organic carbon. The inorganic carbon species in the sample decompose and produces a sharp, characteristic peak. In this heating phase, some of the organic carbon will be transformed into elemental carbon (up to 30%) by pyrolytic conversion, but this can be accounted for by continuously monitoring the sample with a laser. The organic compounds in the sample will become vaporized at these temperatures and become oxidized into carbon dioxide. The carbon dioxide is then mixed with the helium gas flow and transported to a methanator oven, where it is reduced into methane and identified using a flame ionization detector (FID).
2. The sample is then cooled down (to around 525 °C), and the gaseous environment is changed from a pure helium atmosphere to a 2% oxygen/ 98% helium atmosphere. The temperature is increased again, but this time to 850 °C, and at this point, the elemental carbon (and any pyrolyzed organic carbon) become oxidized into carbon dioxide due to the now oxygenated atmosphere. This carbon dioxide is also converted into methane and detected.
3. After all the carbon has been oxidized from the sample, a known volume & concentration of methane is injected into the sample oven, thus, providing for the calibration of each sample analyzed to a known quantity of carbon. Based on the FID response and laser transmission data, the quantities of organic and elemental carbon in the sample are calculated.

Materials

• OC-EC Analyzer
• Sample material