Analytical options

The analytical techniques most often used for the determination of dissolved and particulate trace elements in seawater are  

Selected applications of the various approaches are presented in this chapter (Sections 12.2-12.6). Here the major advantages and/or disadvantages of the analytical techniques are briefly summarized. 

Electrothermal atomic absorption spectrometry (ETAAS) has been the single most important technique in advancing our knowledge of the transition metal distribution in seawater. The graphite-furnace mode is used most frequently. It has the advantage of high sensitivity and therefore small sample volume (e.g., 10-50//L). Major disadvantages are the matrix interferences which usually necessitate a pre-concentration and/or a separation step (see Sections 12.2.1 and 12.2.2). Another application of ETAAS is the cold-vapour technique for the determination of mercury (Section 12.2.4). 

Conventional ICP atomic emission spectrometry (ICP-AES) is not sensitive enough to allow the determination of dissolved trace elements in seawater. It might, however, majorly be applied in the analysis of collected particulate material. The technique combines fast multi-element measurements with somewhat lower investment costs when compared with ICP-MS (see Section 12.6). 

Total-reflection X-ray fluorescence spectrometry (TXRF) is a powerful multi-element method, with detection limits in the pg/mL range, a dynamic concentration range of about 4-5 orders of magnitude and an easy quantification by means of internal standardization. The basic difference between classical X-ray fluorescence and TXRF is the improved beam 

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In order to extend the analytical options of the QCM measurement in cell biology we have introduced an additional low-impedance dipping electrode into the QCM chamber (compare Fig. 14) that serves as a counter electrode to perform electrochemical impedance analysis of the cells grown on the upper gold electrode of the quartz resonator. 

Demonstrating that the analysis be correlated with test data or be performed using standard analysis techniques. If the analytical option is employed for the qualification of valve electric motor operators, (or limit switches or pilot solenoid valves) the methods of analyses will be described in the FSAR. 

In the case of a fully cured adhesive the analytical options are considerably narrowed. Should the curing reaction involve any significant degree of cross-linking, a relatively insoluble matrix will result. Appropriate analytical techniques under these circumstances would include IR (reflective techniques such as specular and diffuse reflectance), pyrolysis GC/MS, and photoelectron... 

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Several of these procedures have an additional advantage of introducing a preconcentration step. Complexation and selectivity using chemically active compounds such as ethylenediaminetetraacetic acid or synthetic ion-exchange materials have been used with considerable success for many years. After extraction there are a number of possible analytical options the resin material may be either analyzed directly by X-ray fluorescence spectrometry or as a solution after digestion or elution of the resin. 

TLC is generally less sensitive and gives worse separation than HPLC. However, it predominates over HPLC in at least two aspects It allows for the analysis of many samples at the same time, and it requires limited sample pretreatment. These features are very important in the analysis of antibiotics, which usually concerns controlling their level in many complicated matrices such as blood, urine, dietary products, and pharmaceuticals. Thus, TLC can be a very useful screening method preceding HPLC analysis. Nevertheless, there are also many examples of analytical applications of TLC, which can achieve selectivity and sensitivity comparable with those characteristic of HPLC. The future of the analytical option in antibiotic analysis is connected with progress in detection and the development of FFPC methods. 

If an exhibit of evidence is consumed in testing, the tests performed on it can never be repeated or verified. While this is not a limitation when the case consists of several milliliters of blood or a large bindle of white powder, other cases are not so simple. If the exhibit is a single fiber or one tiny paint chip, analytical options are limited. Solubility tests would be a poor choice for a single paint chip, but microspectrophotometry (nondestructive) would be ideal. 

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