Glycidyl fatty acid esters in food by LC-MS/MS: method development.

An improved method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the analysis of glycidyl fatty acid esters in oils was developed. The method incorporates stable isotope dilution analysis (SIDA) for quantifying the five target analytes: glycidyl esters of palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2) and linolenic acid (C18:3). For the analysis, 10 mg sample of edible oil or fat is dissolved in acetone, spiked with deuterium labelled analogs of glycidyl esters and purified by a two-step chromatography on C18 and normal silica solid phase extraction (SPE) cartridges using methanol and 5% ethyl acetate in hexane, respectively. If the concentration of analytes is expected to be below 0.5 mg/kg, 0.5 g sample of oil is pre-concentrated first using a silica column. The dried final extract is re-dissolved in 250 µL of a mixture of methanol/isopropanol (1:1, v/v), 15 µL is injected on the analytical C18 LC column and analytes are eluted with 100% methanol. Detection of target glycidyl fatty acid esters is accomplished by LC-MS/MS using positive ion atmospheric pressure chemical ionization operating in Multiple Reaction Monitoring mode monitoring 2 ion transitions for each analyte. The method was tested on replicates of a virgin olive oil which was free of glycidyl esters. The method detection limit was calculated to be in the range of 70-150 µg/kg for each analyte using 10 mg sample and 1-3 µg/kg using 0.5 g sample of oil. Average recoveries of 5 glycidyl esters spiked at 10, 1 and 0.1 mg/kg were in the range 84% to 108%. The major advantage of our method is use of SIDA for all analytes using commercially available internal standards and detection limits that are lower by a factor of 5-10 from published methods when 0.5 g sample of oil is used. Additionally, MS/MS mass chromatograms offer greater specificity than liquid chromatography-mass spectrometry operated in selected ion monitoring mode. The method will be applied to the survey of glycidyl fatty acid esters in food products on the Canadian market.

[HPLC analysis of the active ingredients of Forsythia suspensa].

Forsythia suspensa is a widely used traditional Chinese herb. Because of the need to evaluate its quality, a HPLC method was developed to analyze the active ingredients in its fruits and leaves. One g of powdered plant material was cold macerated over-night with 10 ml of methanol added then supersonic extracted for 20 min. Four ml of the extract were mixed with 1 ml of water, centrifuged (400 x g, 15 min), and then analyzed by HPLC with a Nucleosil C--18 column. The mobile phase for gradient elusion consisted of MeOH(containing 1% tetrahydrofuran) and H2O (containing 0.01 mol/L KH2PO4,pH 3.2) and monitored by UV absorption at 280 nm. The identity and purity of the peaks were checked by photodiode array detector and in comparison with standards. By this procedure, the active constituents caffeic acid, rutin, forsythoside A, forsythin, and forsythigenin were separated successfully, and the quantity of each compound was determined by peak area. Some fruit samples obtained from various sources and the leaf sample made as tea were analyzed by this method.