MONITORING AND LABORATORY DIVISION
STANDARD OPERATING PROCEDURE

S.O.P. No. MLD 065 - Standard Operating Procedure for Organic and Elemental Carbon Analysis of Exposed Quartz Microfiber Filters
 

SCOPE

This document describes the analysis of exposed quartz microfiber filters for organic carbon (OC) and elemental carbon (EC) using a Desert Research Institute (DRI) Thermal/Optical Carbon Analyzer.

SUMMARY OF METHOD

The method is based on the preferential oxidation of organic carbon and elemental carbon compounds at different temperatures.  Organic compounds are volatilized from the sample deposit in a helium (He) atmosphere at low temperatures, while elemental carbon is not oxidized and removed.  The carbon compounds are liberated under temperature and oxidation environments from a small sample using a 5/16 inch diameter punch (0.512 cm2) taken from a quartz fiber filter.  These compounds are converted to carbon dioxide (CO2) by passing the volatilized compounds through an oxidizer (heated manganese dioxide, MnO2).  The CO2 is reduced to methane (CH4) by passing the flow through a methanator (hydrogen enriched nickel catalyst).  A flame ionization detector (FID) is used to quantify the methane.  The optical component of the analyzer is used to correct for pyrolysis of organic carbon compounds to elemental carbon in order to avoid underestimation of OC and overestimation of EC.  The sample reflectance and transmission are continuously monitored by a helium-neon laser and a photodetector throughout an analysis cycle.  When pyrolysis takes place, there is an increase in light absorption resulting in a decrease in reflectance and transmission.  Thus, by monitoring the reflectance/transmission, the portion of the elemental carbon peak corresponding to pyrolyzed organic carbon can be correctly assigned to the organic fraction.