ABSTRACT
Trans-fatty acids (TFA) are geometric isomers of naturally occurring cis-fatty acids. High dietary TFA intake has been associated with risk factors for cardiovascular disease. However, little is known about TFA levels in humans. To address this data need, we developed and validated a new isotope dilution-gas chromatography-negative chemical ionization-mass spectrometry (ID-GC-NCI-MS) method for quantitation of 27 fatty acids (FA) including 4 major TFA in human plasma, serum, and red blood cells (RBC) from 66 donors. Quantitation was performed with 18 isotope labeled internal standards and results are presented in µM and % of total FA. This method has high sensitivity and specificity due to use of pentafluorobenzyl-bromide derivatization combined with NCI-MS and a 200m column to optimize positional and geometric FA isomer separation. The four major TFA, palmitelaidic acid, elaidic acid, trans-vaccenic acid, and linoelaidic acid, were detected in all samples, with median total TFA concentrations of 17.7µM in plasma, 19.6µM in serum, and 21.5µM in RBC. The % of total FA for the TFA was 0.20% in plasma, 0.20% in serum, and 0.30% in RBC. Patterns for % FA are similar to those reported in other studies. We developed a highly specific, ID-GC-NCI-MS method to quantitate TFA and other FA in humans.
Subject(s)
Gas Chromatography-Mass Spectrometry/methods , Trans Fatty Acids/blood , Humans , Linear Models , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
A novel liquid chromatographic (LC) method with repeated injections of Suwannee River Fulvic Acid (SRFA) was used to investigate its adsorptive fractionation by synthetic α-Al(2)O(3). Eluent (i.e., non-retained) SRFA for each injection was monitored by two ultraviolet (UV) absorbance detection channels (300 and 365 nm) and one fluorescence detection channel (λ(ex)=350 nm, λ(em)=450 nm). Preferential adsorption of SRFA constituents was revealed by the different responses of the three LC detection channels. Samples of non-retained SRFA from injections of three independent replicate experiments were collected and aggregated for subsequent analysis by steady state ultraviolet-visible (UV/vis) absorption spectrometry and size exclusion chromatography (SEC). The ratio of absorbance at 254 and 204 nm, a surrogate for specific UV absorbance at 254 nm, increased with increasing injection number for the non-retained SRFA, indicating the preferential adsorption of SRFA constituents containing aromatic moieties. SEC analysis confirmed the preferential adsorption of higher molecular weight (MW) SRFA constituents as the non-adsorbed SRFA fractions increased in MW across the series of injections. The SEC results also suggested that certain SRFA constituents in the ca. 2-5 kDa MW range adsorbed in early injections were displaced by higher MW species (ca. 5-10 kDa) in later injections.