Author
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Reeves Iii, James |
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Submitted to: Popular Publication
Publication Type: Popular Publication Publication Acceptance Date: 1/5/2008 Publication Date: 1/5/2008 Citation: Reeves III, J.B. 2008. Near- and Mid-Infrared Reflectance Spectroscopy for the Quantitative and Qualitative Analysis of Agricultural Products. Popular Publication. Interpretive Summary: The composition of a wide variety of agricultural products including grains, forages and animal wastes has come to be determined through the interaction of light radiation, mainly beyond the range of human site, in a process known as near-infrared spectroscopy (NIRS). More recently, diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) using infrared or heat radiation has similarly been shown to be able to determine the composition of dried, ground agricultural samples including forages and grains, but especially soils. However, there is a great deal of misunderstanding about what is involved in developing the calibrations (equations relating the spectral information to the sample composition) needed to determine the composition of products from their near- or mid-infrared spectra. The process involved in converting spectral and compositional data into equations able to predict the composition of new samples from their spectra has come to be known as chemometrics. Indeed to a great extent the term NIRS has come to mean both a spectral region and a process involving spectrometry, statistics and chemistry all rolled into one. While a spectrometer may provide the spectra, various laboratory methods the reference data and chemometrics the mathematical and statistical tools to process the spectroscopic data, many other factors are involved in the process including how to select the proper samples and even the quality of the reference values used. For example, one of he biggest results of the entire process of NIRS has been the improvement in reference methods (standard laboratory method used to determine composition) as practitioners of NIRS discovered just how unreliable many laboratory methods. Another important aspect of calibration development is the calibration maintenance (updating or developing new calibrations) required as samples change with time due to anything from the weather to natural variations in sample composition or the development of new varieties. This presentation discusses sample requirements, instrumentation and the process of developing and maintaining spectroscopic calibrations using NIRS and DRIFTS for quantitative and qualitative analysis of soils and other agricultural materials and products including the advantages and disadvantages of each spectral region. Technical Abstract: For several decades near-infrared diffuse reflectance spectroscopy (NIRS) has been used to determine the composition of a variety of agricultural products. More recently, diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) has similarly been shown to be able to determine the composition of ground, but non-KBr diluted samples. However, there is a great deal of misunderstanding about what is involved in developing the calibrations needed to determine the composition of products from their near- or mid-infrared spectra. In order to predict the composition of samples from their spectra, calibrations relating spectral information to composition are needed. This process has come to be known as chemometrics. Indeed to a great extent the term NIRS has come to mean both a spectral region and a process involving spectrometry, statistics and chemistry all rolled into one. While a spectrometer may provide the spectra, various laboratory methods the reference data and chemometrics the mathematical and statistical tools to process the spectroscopic data, many other factors are involved in the process including how to select the proper samples and even the quality of the reference values used. For example, one of he biggest results of the entire process of NIRS has been the improvement in reference methods as practitioners of NIRS discovered just how unreliable many laboratory methods, both wet chemical and instrumental are. Another important aspect of calibration development is the calibration maintenance required as samples change with time due to anything from the weather to natural variations. This presentation discusses the sample requirements, instrumentation and the process of developing and maintaining spectroscopic calibrations using NIRS and DRIFTS for quantitative and qualitative analysis of soils and other agricultural materials and products including the advantages and disadvantages of each spectral region. |
