Perspectives on Quantitative Mid-FTIR Spectroscopy in Relation to Edible Oil and Lubricant Analysis: Evolution and Integration of Analytical Methodologies

Abstract

Over the past 20 years, Fourier transform infrared (FTIR) spectroscopy has evolved to become an important tool for quantitative analysis, and its application to edible oil analysis has been an active area of research. This paper reviews the evolutionary development of methodology for FTIR analysis of edible oils in our laboratory, focusing on strategies and techniques used to quantitate a variety of common edible oil quality control parameters, such as free fatty acid content, iodine value, saponification number, peroxide value, solid fat index, trans content, moisture content, anisidine value, etc., as well as conceptual, instrumental, and software/automation innovations originating in related work on lubricant analysis. In our initial development of FTIR methods for edible oil analysis, the calibration approaches employed were mainly based on partial-least-squares regression using either molecular model systems or process samples. Subsequently, the concept of signal transduction was developed as a means of facilitating the routine implementation of some of these FTIR methods and was also considered for the analytically related lubricant sector. However, the viscosity, complexity, and matrix variability of in-service lubricants required new approaches, while the high sample volumes common to the field made automation a prerequisite. These issues were addressed through the use of signal transduction in combination with dilution as well as extraction techniques to facilitate automation while maintaining quantitation. A related concept, termed spectral reconstitution, was initially developed to speed up the qualitative condition monitoring of in-service lubricants. Spectral reconstitution was subsequently successfully applied to trans analysis in edible oils and was shown to provide a generalized means for high-volume FTIR transmission analysis of viscous oils. This technique has since been adapted to quantitative peroxide value and free fatty acid analysis, allowing for throughputs of up to 120 samples per hour. These developments represent the integration of analytical methodologies for the edible oil and lubricant sectors, with potential for extension to the fuel sector as triacylglycerols become a feedstock for biodiesel.