In 2006, the US FDA mandated the declaration of the total trans fat content on the Nutrition Fact label of foods including dietary supplements when a product contained 0.5 or more grams of trans fatty acid per serving; the minimum corresponding trans fat content is estimated to be approximately 2% of total fat. The FDA definition is based on chemical structure and includes only fatty acids with one or more isolated double bonds in the trans configuration. Several issues negatively impacted the sensitivity of the current official infrared (IR) methods, thus limited the quantitation of trans fat to 5% of total fat. To improve sensitivity and accuracy and to meet the labeling requirement, a new internal reflection IR procedure called negative second derivative is described and evaluated for the quantitation of total trans fat in the present study. The enhanced spectral features of a second derivative resolved issues that traditionally limited the sensitivity of the IR methodology. Calibration standard mixtures starting at approximately 0.5% trielaidin in the total fat (tripalmitin or triarachidin) were successfully generated and used to determine the trans fat levels for unknown test samples with trans content as low as approximately 1% of total fat. Quantitative IR data were compared to those obtained by gas chromatography and were found to be in good agreement.

The mandatory requirement in many countries to declare the amount of trans fat present in food products and dietary supplements has led to a need for sensitive and accurate methodologies for the rapid quantitation of total trans fats and oils. Capillary gas chromatography (GC) and infrared spectroscopy (IR) are the two methods most commonly used to identify and quantify trans fatty acids for food labeling purposes (see the article by Delmonte and Rader in this ABC issue for a detailed presentation of GC methodology). The present article provides a comprehensive review of the IR technique and the current attenuated total reflection (ATR) Fourier-transform (FT) IR methodologies for the rapid determination of total trans fats and oils. This review also addresses potential sources of interferences and inaccuracies in FTIR determinations, particularly those done at low trans levels. Recent observations have shown that the presence of saturated fats caused interferences in the FTIR spectra observed for trans triacylglycerols. The recognition and resolution of previously unresolved quantitative issues improved the accuracy and sensitivity of the FTIR methodology. Once validated, it is anticipated that the new negative second-derivative ATR-FTIR procedure will make IR spectroscopy more suitable than ever, and a rapid alternative and/or complementary method to GC, for the rapid determination of total trans fats for regulatory compliance. Figure Infrared light bouncing inside an internal reflection crystal.

The mandate to label food products with the content of total trans fatty acids has led to an increase in demand for sensitive and accurate methodologies for the rapid quantitation of trans fats. Unfortunately, the latest official infrared (IR) spectroscopic method lacks the required sensitivity. A more sensitive IR procedure that requires the measurement of the height of the second derivative (2D) of the trans absorption band at 966 cm -1 was recently proposed; however, a reported inconsistency at low trans levels between GC (0% of total fat) and IR (1.2% of total fat) results for a fully hydrogenated vegetable oil could not be reconciled, and triggered further investigations. For the first time, we recognize and report the presence of weak interference bands (962-956 cm -1 ) attributed to saturated fats in the IR spectra of trans fats; these interference bands have an adverse impact on the sensitivity and accuracy of the IR determination at low trans levels (£0.5% of total fat). Therefore, weak spectral features observed at energies below the one expected for trans bands (966 cm -1 ) in test samples high in saturated fat (coconut oil and cocoa butter) must not be mistaken for trans bands. Tristearin TL Trilaurin TM Trimyristin TP Tripalmitin TA Triarachidin Since trans fat labeling requirements became mandatory in the US, Canada and many other countries [1], there has been an urgent need for accurate analytical methodologies that would facilitate the verification of compliance with the various regulations. The determination of total trans fatty acids by IR has been a widely used procedure [2] that has been standardized [3-6]. Its importance stems from the fact that the C-H out-of-plane deformation band observed at 966 cm -1 is uniquely characteristic of isolated double bonds with trans configuration. These double bonds are found in trans-monoenes, and in methylene-interrupted and non-methylene-interrupted trans,trans-dienes, mono-trans-dienes, and mono-trans-trienes. All these different fatty acids exhibit that same absorption band at 966 cm -1 regardless of chain length or position of the isolated trans double bond. Thus measuring the intensity of the absorption of the trans band effectively adds up all the different fatty acids containing isolated M. M. Mossoba (&) Food and Drug Administration, Abbreviations IR Infrared HSBO Hydrogenated soybean oil TS

With the tremendous growth in the semiconductor and coatings industries, spectroscopic methods of examining extremely thin films on high refractive index substrates have become increasingly important. One infrared method for analyzing monolayers on substrates such as silicon and gold that has recently gained popularity is 'grazing' or high angle of incidence attenuated total reflection (ATR) spectroscopy. This paper investigates the directional electric field strengths and the extraordinary sensitivity achieved by using the grazing angle ATR method for analyzing monolayers on silicon substrates.

In this paper, the suitability of using the Kramers-Kronig transform to routinely extract optical constants from near-normal incidence reflectance spectra of solids and liquids is demonstrated. In addition, the possibility of utilizing the Kramers-Kronig transform as a linearizing transform for near-normal incidence reflectance spectra is investigated. Also, several commercial Kramers-Kronig software packages were utilized in determining the optical constants from the near-normal incidence reflectance of Plexiglas. Unexpectedly, the results produced by the various packages differed significantly. The near-normal reflectance of water was measured, the Kramers-Kronig transform was applied to extract the optical constants of water, and the result was compared to values found in the literature. Furthermore, the Kramers-Kronig transforms of near-normal incidence reflectance spectra of various concentrations of sugar in water were calculated to evaluate its use as a linearizing transform for quantitative applications.