Quantitative Gas Chromatographic Method for C16:1t9, C18:1t9, C18:1t11, and C18:2tt9,12 trans Isomers Using Negative Chemical Ionization and Stable Isotope Internal Standards

Abstract

Trans fatty acids have long been associated with risk factors for cardiovascular disease, thus making their consumption a major public health concern. Since the individual trans isomers of fatty acids typically make up less than 5% the total fatty acid content in a given biological matrix, epidemiological studies on the subject have been difficult. In addition, the absolute concentrations of these analytes were oftentimes subject to high variability in earlier reports. As part of the CDC's ongoing biomonitoring activities, we report an improved, highly sensitive GC/MS method that enables the measurement of 31 fatty acids including the trans fatty acids C16:1t9, C18:1t9, C18:1t11, and C18:2tt 9,12 in human plasma. At present, no other methods reported in the literature have been able to detect all of the aforementioned trans isomers in a single chromatographic separation.In a set of 35 anonymous individuals, the median concentrations and ranges for the trans fatty acids were 0.0062 (0.0039‐0.0281), 0.0387 (0.0147‐0.2056), 0.0557 (0.0196‐0.5546), and 0.0016 (0.0000‐0.0074) µM for C16:1t9, C18:1t9, C18:1t11, and C18:2tt 9,12, respectively. The sum total concentration of the fatty acids analyzed was 12.13 µM. Therefore, the aforementioned trans fatty acids comprised only 0.73% of the fatty acids quantitated for this assay. The method reported herein will allow for more detailed studies on trans fatty acid intake and health effects associated with this intake.