Sample preparation, general environmental analysis

Sometimes the sample preparation is a difficult problem, especially in clinical and environmental chemistry. General procedures are filtration (perhaps by means of a dedicated membrane which retains compounds selectively), solid phase extraction with disposable cartridges (also with dedicated selectivity), protein precipitation and desalting. A special case is sample preparation for biopolymer analysis. 

Nitrite and nitrate may also be determined by HPLC using anion-exchange columns with either UV absorption or electrochemical detection. These methods are generally used for environmental samples and urine where fewer interfering compounds exist. The more extensive sample preparation and analysis time have limited its use for biological samples. 

Despite the remarkable sensitivity of modern instrumental detection techniques, analysis of environmental water samples nearly always requires enrichment of the analytes. This, together with separation from the matrix, are the two main functions of sample preparation appropriate sample preparation techniques address both issues at the same time, while striving to impose as few restrictions as possible on the subsequent instrumental determination (separation and detection). Sample preparation is strongly dependent on the nature of the analyte and the matrix, particularly with regard to its volatility and polarity. Figure 13.8 gives a general overview of common sample preparation (enrichment) techniques for aqueous and other matrices. 

In this section a concise overview of the most widely used analytical procedures for the determination of PCBs in environmental matrices (namely, air, sea water, snow/firn/ice, sediment/soil and biota) is given. Regardless of the nature of the sample, the following steps are generally included in an analytical procedure i) sample collection and storage ii) sample preparation (extraction of the analytes and cleanup of the extract) iii) instrumental analysis iv) data evaluation, including analytical quality control. 

Whether the ionization is positive or negative, TIMS requires careful sample preparation, often involving considerable chemical processing to separate and purify the element of interest. TIMS finds applications in geoscience, environmental analysis, cosmochemistry, biosciences, medicine, material science, and physics. Samples generally include soil, minerals, meteorites, and biological tissue. More information on the specifics of the TIMS technique and its applications is in the monograph by De Laeter (2001). 

Although it is beyond the scope of this article to consider detailed collection and sample preparation procedures for environmental samples, here are some general considerations for speciation analysis of air, water, biological material, and soils/sediments. The collection of samples in air has focused upon the determination of hydrides and methylated compounds of elements such as arsenic, lead, mercury, and tin. The sample may be introduced into a preevacuated container, or with a pump. The analytes may be isolated using cryotrapping techniques or adsorbent cartridges. For best results, it is recommended to collect the entire gas sample in a container, coated... 

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