Submitted to: Pittsburg Conference on Analytical Chemistry and Applied Spectroscopy
Publication Type: Abstract Only
Publication Acceptance Date: March 8, 1996
Publication Date: N/A
Technical Abstract: Sustainable agriculture requires that resource managers address the soil quality issues of fertility, erodability, aggregate formation and stability, and effectiveness as an environmental buffer. Each of these attributes is a manifestation of the composition and molecular structure of whole soil. Soils of the Midwest contain calcareous mineral components. FTIR with photoacoustic sampling (PAS) is used to estimate the carbonate mineral content of soils taken from two farm fields in Iowa. Spectra are recorded on a Model FTS-60A spectrometer (BIO-RAD, Digilab Division, Cambridge, MA) with dry air purge of the 896 interferometer and configured with a Model 200 photoacoustic detector (MTEC, Inc., Ames, IA). PAS patterns are collected between 4000-500 cm**-1 at a resolution varying between 4 cm**-1 and 0.25 cm**-1. Acquired data are processed on an SPC 3200 Data Station running IDRIS Software, v. 3 on a UNIX platform. Higher resolution allows isolation of bands from possible interferences. Mid-IR bands within the 2700-2400 cm**-1 and the 1819-1739 cm**-1 windows are used for both qualitative characterization and quantitative estimation. A standard addition technique employing either a principal component analysis (PCA) approach or a partial least squares (PLS) approach is used for quantitation. A user-generated library of spectra of representative carbonate minerals is also developed to help in identification. Minimum detection limit for this approach is approximately 0.5% total carbonate by weight. Particle-size based fractionation of test soils is used to illustrate the relationship between size and carbonate mineral content.