| Many reasons exist for analyzing soils ? forensics, remediation, and total organic content analyses are three examples. Several aspects of soil are of interest, including both inorganic and organic content. The former is typically analyzed by elemental methods (AA or ICP), while organic content is in most cases measured by mass loss upon pyrolysis. This method alone does not identify the organic material, it only gives an estimate of total organic content.
Recent studies (referenced in the note) have described a forensic analysis of soil based on IR spectroscopy. The basic method involves subtracting transmission spectra before and after pyrolysis, with the general assumption that missing peaks represent organic material removed during heating. This represents an excellent first step in the analysis of soil, and is quite simple to implement, but it misses the important information which can be derived from the gases emitted during the heating step. This note demonstrates how this method can be expanded upon using TGA-IR.
In a thermo-gravimetric analysis (TGA), a sample is heated and the weight loss is determined using a microbalance. The gases driven off can be fed into a gas transmission cell in a FT-IR for identification during the TGA run. This adds considerable information to the TGA experiment, and has been used many times in failure analyses.
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