Nonvolatile triacylglyceride (TAG) oxidation products play an important role in the oxidative degradation of lipids. They serve as a reservoir of oxygen-containing species and hence can act as off-flavor precursors or as initiators for further oxidation reactions. Possible nonvolatile lipid oxidation products are TAG with a hydroperoxy, hydroxy, epoxy, or oxo (ketone or aldehyde) group or combination of these groups. The breakdown of TAG hydroperoxides yields nonvolatile glyceride species with two intact fatty acid chains and one short chain mostly ending in an aldehyde or hydroxy group (2 1 / 2 glycerides). By means of normal-phase high-performance liquid chromatography (HPLC) with mass spectrometric (MS) detection, nonvolatile lipid oxidation products can be separated according to polarity. This results in separation into classes of TAG oxidation products, such as epoxy-TAG, oxo-TAG, hydroperoxy-TAG, hydroxy-TAG and 2 1 / 2 glycerides, which can be identified using selected ion chromatograms. The retention times of TAG oxidation products on the normal-phase HPLC system and the signal intensity of the MS detector are stable enough to enable quantitative analysis based on external calibration. The normal-phase HPLC-MS method is very suitable for the characterization and quantitation of nonvolatile TAG oxidation products in oxidized TAG reference compounds as well as in real oils or oil phases isolated from emulsions, spreads, or other fat-based food products. This method can give detailed information for the study of lipid oxidation mechanisms.

Abstract. An automated procedure for the analysis of aqueous samples by membrane disk extraction coupled on-line to capillary gas chromatography (GC) is presented. Organophosphorus pesticides are preconcentrated from aqueous samples on three 0.5 mm thick, 4.0 mm diameter XAD-2 membrane extraction disks which are mounted in a polymer holder for use in a PROSPEKT sample processor. The layers are dried by a stream of nitrogen (30 min at ambient temperature). Desorption of the analytes is carried out with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an early solvent vapor exit. The method is a fully software-controlled automated system, and includes sample preparation, sample transfer and GC analysis. The final analysis is carried out by GC with nitrogen-phosphorus (NPD) or mass-selective detection. The technique is applied to the determination of a series of organophosphorus pesticides in tap water and water from European rivers. With a sample volume of only 2.5 mL, the detection limits achieved with the NPD were 20-50 ng L-' in tap water and 20-100 ng L-' in river water.

Plant sterols are added as their FA esters to vegetable oil table spreads at levels of approximately 8% as a means to reduce blood cholesterol levels. A new chromatographic method was designed to quantify quickly the level of plant sterol FA esters in incoming (raw) materials and to monitor their processing and final product quality with respect to total sterol level. The method shows a significant improvement in elapsed time and thus labor cost over the classical methods for sterols published in normative references. This improvement was obtained together with high performance characteristics, as shown by the internal method validation for recovery and repeatability. Its validity and robustness were further tested and confirmed in an international collaborative test. The method allows monitoring of sterol content of raw materials, fat-blends, and consumer products at the target level, with a range of 10% or less around this target. The calculated within-and betweenlaboratory reproducibility were 0.680 and 1.194 w/w%, respectively, for sterol-containing spreads. The results afforded by this method can be used for setting tight product specifications or to monitor trade between companies. We propose to add this new and fast method for total 4-desmethyl sterol(s) to analytical method collections as an adjunct to methods already listed for more detailed sterol analysis.Plant sterols (PS) and plant sterol FA esters (PSE) are recognized for their therapeutic efficacy in lowering blood cholesterol levels. Recent reviews on the pharmacological properties of PS and their fully saturated isomers (stanols) focus on this cholesterol-lowering effect (1,2). The blood cholesterol-lowering (BCL) effect of sterols, in particular the 4-desmethyl sterol(s) such as sitosterol, has been known since the 1950s. With the use of the FA esters instead of the free PS, a wider range of formulation options exists. The new interest and formulation options have resulted in a range of consumer products, such as vegetable-oil table spreads, designed to lower total blood cholesterol and LDL-cholesterol (3). The normal daily intake of about 20 g of a vegetable fat spread containing 8% PS, equivalent to 13-14% PSE, reduces the LDL-cholesterol by about 10% (4). With the use of PS and PSE at these elevated levels, these natural edible oil constituents have become functional food ingredients. Sterols used for the BCL effect are mixtures of mainly 4-desmethyl sterol(s) (sitosterol, campesterol, stigmasterol, and brassicasterol).To support quality control of raw materials, processing, and final consumer product control at these levels, a new and fast total sterol analysis for the content of mainly 4-desmethyl sterol(s) has been developed, validated, and collaboratively tested. The method is designed for a total content of these 4-desmethyl sterol(s) in a range of approximately 15-20% for vegetable oil blends, 8% in consumer products such as spreads, and approximately 60% in PSE concentrates. A new method was necessary because current analytical methods...

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An overview is presented of methods currently in use to combine the preparation of aqueous samples on-line with capillary gas chromatography. Two approaches can be distinguished: heartcut-orientated reversed-phase liquid chromatography-gas chromatography (GC) and analyte-isolation-orientated analyte extraction-GC. These approaches either use techniques in which water is directly introduced onto the GC column, or an indirect approach in which water is eliminated, i.e., by solid-phase extraction, solid-phase microextraction or liquid-liquid extraction, prior to introduction of the analytes onto the GC column. The latter type of approach is much more successful and user friendly, and many applications have been reported.

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