Sample Extraction and Handling

Sample extraction procedures are often perceived as bottlenecks in analytical methods, as they may be time consuming and require particular attention. In most developed analytical techniques, lipids extraction represents a crucial task and the first step of an efficient analytical method, since the validity of the results depends on proper sampling and sample handling preparation prior to analysis. The task of lipid sample extraction, preparation, and handling has been comprehensively discussed, recently [21], 

As a first requirement, the sample analyzed should represent as closely as possible the lipid composition of the whole matrix from which it was taken furthermore, sample preparation should be carried out in such an environment as to minimize any changes in lipid properties prior to analysis. In food analysis, proper sampling of the lipid fraction requires knowledge of the physical structure and location of the major lipids in the sample, and the choice of the most adequate procedure depends on the t)q)e of food being analyzed, the nature of the lipid fraction, as well as the analytical procedure applied for the extraction. Foods consisting almost entirely of lipids, such as vegetable oils, often require little, if any, sample preparation prior to analysis. Qn the other hand, for more complex foods, such as meat or milk, extraction and purification of the lipid fraction is necessary prior to analysis. Official methods have been developed, which recommend the sample preparation and extraction procedures to be followed for a specific t)q5e of food. Solvent extraction methods are usually used, to separate lipids from water-soluble food components, prior to chromatographic analysis these are described in the sections that follow. A number of steps are usually required, prior to the solvent xtraction of lipids from a matrix  

After the extraction, lipids may be subjected to further treatment, like filtering or centrifugation, and are usually dried to remove any residual moisture, which may alter the analysis that follows. Since unsaturated lipids are prone to auto-oxidation and formation of off-flavors and harmful products can occiu within any of these analytical steps, a number of precautions are usually taken, to keep oxidation to a minimum. These consist of the addition of antioxidant agents, the use of a nitrogen atmosphere, as well as control of the exposure to light and temperature. 

Ihie disadvantages of this procedure are poor extraction of polar lipids, long time involved, large volumes of solvents, and the hazards of 

The use of chlorinated solvents is prohibited for health reasons in many laboratories, and this poses a major limitation to the use of the Folch, Lees, and Stanley method. Unfortunately, there seems to be no satisfactory substitute to this solvent in many analytical procedures for lipid analysis. As a general rule, all solvents should be used in well-ventilated areas or in fume cupboards inhalation and contact with skin should be avoided and the analyst should keep in mind that toxic hazards may exist with all chemicals, even if they have not been investigated yet. 

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As sample extraction and sample handling are of general consideration for the more exotic biological matrices often found in food analysis, the application of IPCR in the research project MYCOPLEX [89], founded by the European Union, promises interesting new developments. This project is dedicated to the detection by IPCR of ochra- and aflatoxins in milk and coffee, focusing on sensitivity and simplified antigen extraction by dilution of the samples. 

There is a need in both the laboratory and process reactors to minimize the time delay between sample extraction and analysis results if the data are going to be used effectively to determine an end point or be used for feedback control. For these reasons, there has long been a desire for process analyzers to be able to collect data directly from the process stream itself without the need for a sample-handling system. Conceptually, one could simply mount the analyzer to the process stream to accomplish this goal. In reality however, safety, maintenance, environmental, and other practical concerns make this undesirable. 

Classical LLEs have also been replaced by membrane extractions such as SLM (supported liquid membrane extraction), MMLLE (microporous membrane liquid-liquid extraction) and MESI (membrane extraction with a sorbent interface). All of these techniques use a nonporous membrane, involving partitioning of the analytes [499]. SLM is a sample handling technique which can be used for selective extraction of a particular class of compounds from complex (aqueous) matrices [500]. Membrane extraction with a sorbent interface (MESI) is suitable for VOC analysis (e.g. in a MESI- xGC-TCD configuration) [501,502]. 

Nowadays, MS is often no longer the analytical bottleneck, but rather what precedes it (sample preparation) and follows it (data handling, searching). Direct mass-spectrometric methods have to compete with the separation techniques such as GC, HPLC and SFC that are commonly used for quantitative analysis of polymer additives. Extract analysis has the general advantage that higher-molecular-weight (less-volatile) additives can be detected more readily than by direct analysis of the polymer compound. 

No sample handling between extraction and separation (no contamination)... 

In the past two decades quite a few new techniques have emerged for the treatment of aqueous samples prior to organic analysis. Perhaps the most important development is that of solid-phase extraction (SPE), which has successfully replaced many off-line steps. This technique can be considered to have introduced a genuine new era in sample handling [1]. The many varieties in which the technique is available and can be applied have made it the key step in handling of aqueous samples. Among the successful varieties are solid-phase microextraction (SPME), matrix solid-phase dispersion, disk extraction and immunosorbent extraction. Several reviews covering these topics have appeared in the literature in the past decade (see e.g. Refs. [2,3] for nonylphenol... 

Albro PW. 1979. Problems in analytic methodology Sample handling extraction and cleanup. In Nicholson WJ, Moore JA, eds. Annals of the New York Academy of Sciences, Health Effects of Halogenated Aromatic Hydrocarbons International Symposium, New York, NY, USA, June 24-27, 1978. New York, NY New York Academy of Sciences, 320 19-27. 

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