Comparison of attenuated total reflection infrared spectroscopy to capillary gas chromatography for trans fatty acid determination

Gas chromatography (GC) has been a standard analytical tool in lipid chemis try. The rapid attenuated total reflection (ATR) infrared (IR) American Oil Chemists' Society (AOCS) Recommended Practice (Cd 14d-97) was compared to the capillary GC AOCS Recommended Practice (Ce 1f-97) that was optimized to accurately determine total trans fatty acids on highly polar stationary ph ases. This comparative evaluation was validated in an independent laborator y. These procedures were used to quantitate the total trans fatty acid leve ls in partially hydrogenated vegetable oils, measured as neat(without solve nt) triacylglycerols (TAG) by ATR and as fatty acid methyl ester (FAME) der ivatives by capillary GC. Unlike FAME, TAG determination by ATR required no derivatization, but samples had to be melted prior to measurement. Five bl ind replicates for each of three accuracy standards and three test samples were analyzed by each technique. The GC and ATR determinations were in good agreement. Accuracy was generally high. The ratios of ATR mean trans value s (reported as percentage of total TAG) to the true values (based on the am ount of trielaidin added gravimetrically) were 0.89, 0.98, and 1.02 for acc uracy standards having about 1, 10, and 40% trans levels. The corresponding GC values, determined as percentage of total FAME, were 0.98, 0.99 and 1.0 4. The ratios of mean trans values determined by these techniques were ATR/ GC 0.85, 1.04, and 1.01 for test samples having trans levels of about 0.7, 8, and 38%, respectively. The optimized GC procedure also minimized the exp ected low bias in trans values due to GC peak overlap found with the GC Off icial Method Ce 1c-89. Satisfactory repeatability and reproducibility were obtained by both ATR and GC.