Organic analysis sample preservation

Because of their diversity and complexity as well as the gradual internationalization of the different standards, it has proven necessary to standardize the methods of sample preservation, handling, fractionation, and analysis throughout the chain of separation and treatment. All these stages are the object of precise protocols established by official national and international organizations. They describe in as minute detail as possible the procedures employed not only for each analysis but very often giving different procedures for the same analysis in different matrices. These are the standards or standardized methods discussed in Chapter 7. 

Preservation of organic samples is thus still a major problem there is no general, foolproof method applicable to all samples and all methods of analysis. The most generally accepted method of sample preservation is storage under refrigeration in the dark, with a preservative. This is another area that still needs extensive investigation. 

Based on the their knowledge of contaminant degradation in samples, the EPA and other professional organizations involved in sampling and analysis derived the requirements for container types and materials, sample preservation, and holding time. These requirements for soil and water samples are summarized in Appendices 12 and 13. 

Common to nearly all analyses is preservation with refrigeration at 2-6°C, a practice, which minimizes the volatilization of organic compounds with low boiling points and the bacterial degradation of most organic compounds. That is why we must place samples on ice immediately after they have been collected, ship them in insulated coolers with ice, and keep them refrigerated until the time of analysis. Water samples collected for metal analysis and preserved with nitric acid are an exception to this rule as they may be stored at room temperature. The addition of methanol or sodium bisulfate solution to soil collected for VOC analysis is the only chemical preservation techniques ever applied to soil samples. 

Once the sample preparation is complete, the analysis is carried out by an instrument of choice. A variety of instruments are used for different types of analysis, depending on the information to be acquired for example, chromatography for organic analysis, atomic spectroscopy for metal analysis, capillary electrophoresis for DNA sequencing, and electron microscopy for small structures. Common analytical instrumentation and the sample preparation associated with them are listed in Table 1.1. The sample preparation depends on the analytical techniques to be employed and their capabilities. For instance, only a few microliters can be injected into a gas chromatograph. So in the example of the analysis of pesticides in fish liver, the ultimate product is a solution of a few microliters that can be injected into a gas chromatograph. Sampling, sample preservation, and sample preparation are... 

A trip blank is shipped to and from the field with the sample containers. It is not opened in the field and, therefore, provides a test for contamination from sample preservation, site conditions, and transport as well as sample storage, preparation, and analysis. It is most commonly used for volatile organics. 

Although this section will focus on trace organic toxic chemical sampling, preservation, and analysis, the protocols and procedures that are outlined can be applied (with less complexity) to trace inorganic toxic chemicals. 

See also Atomic Absorption Spectrometry Principles and Instrumentation. Chemiluminescence Overview. Chromatography Overview. Flow Injection Analysis Principles Instrumentation. Ion-Selective Electrodes Overview. Quality Assurance Quality Control Reference Materials. Sample Handling Sample Preservation. Sampling Theory. Water Analysis Overview Organic Compounds. Water Determination. 

Tupas L.M., Popp B.N., and Karl D.M. 1994. Dissolved organic carbon in oligotrophic waters experiments on sample preservation, storage, and analysis. Mar. Chem. 45 207-216. 

TABLE 15.3 Sample Handing and Preservation of Environmental Samples Requiring Organic Analysis... 

Sample preparation used to extract proteins from cells prior to analysis is an important step that can have an effect on the accuracy and reproducibility of the results. Proteins isolated from bacterial cells will have co-extracted contaminants such as lipids, polysaccharides, and nucleic acids. In addition various organic salts, buffers, detergents, surfactants, and preservatives may have been added to aid in protein extraction or to retain enzymatic or biological activity of the proteins. The presence of these extraneous materials can significantly impede or affect the reproducibility of analysis if they are not removed prior to analysis. 

Data from the Na-pyrophosphate partial extractions and estimates of organic C contained in humic and fulvic acids from spectroscopic determinations show poor reproducibility over time. Analysis of data from re-sampling in September 2007 show significantly lower results over bedrock mineralisation than the original orientation survey conducted in April 2007, although the general pattern appears to be preserved. Re-analysis of the duplicate field samples in the same batch indicates that this variation largely reflects seasonal variations in metal content of the soils, possibly related to rainfall patterns, but also includes a component of laboratory variation between batches. 

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