Analytical method transfer dissolution

The small vessel and minipaddle dissolution method described in Table 10.7 has been extensively used by the originating laboratory. In addition, the method was successfully transferred to several laboratories, demonstrating the method s reproducibility and ruggedness. The data for the analytical method transfer exercise (AMTE) to one of these laboratories is shown in Table 10.7. The AMTE used a bracketing... 

In the past, the practice has been to take a sample from any depth in a large metal or (better) plastic container and then transfer the sample to another, usually plastic, container for subsequent analysis by appropriate analytical methods. Obviously, a metal container will contribute to the trace metal content of the sample, and even plastic containers will cause problems. Trace analysis studies have shown that plastic or glass sample containers can both absorb trace metal ions from the sample and/or contribute other metal ions to solution by surface dissolution 12, 13), Thus, the sample cannot be analyzed accurately because of the time-dependent effects on concentration which are related simply to the nature of the container and the conditions used to store the sample. 

The passive corrosion current density ic can be measured with appropriate analytical methods. For iron, measurements with the RRD electrode allow to measure the dissolution of Fe + ions by their reduction to Fe " at the ring [10]. The transfer efficiency between the disk and the ring is about 70% and may be calculated from the geometry of the Fe-disk and Pt-ring electrodes (radius of disk and ring and distance ring-disk) [33]. It can also be... 

Figure 5.30 shows how many parameters have to be faken into account, the metal fractions Xa and Xg at the metal surface, fhe cationic and anionic fractions within the film, and fhe dissolution rates of A and B af fhe film surface. Furthermore, the different transfer rates of fhe cations may cause a gradient in the layer composition. Finally, the cations A and B + may be further oxidized at sufficiently positive potentials causing a distribution of lower and higher valent species within the film. This in turn requires the knowledge of the semiconducting properties that are involved in the oxidation of cations as well as the reactions of redox systems at the film surface, which require electron conduction across the layer. All these details show that the semiconductor properties and the chemical composition and structure have to be studied with appropriate tools. The complexity of these systems requires the application of surface analytical methods in order to understand the properties of these films and their influence on the corrosion properties of alloys. 

Precipitation is one of the oldest separation techniques used in classical chemical analysis. However, its importance in modem analytical chemistry has declined due to the development of more versatile and efficient separation techniques such as solvent extraction and ion-exchange which are also more easily automated. Conventional operations for precipitation in the batch mode are both labour and time consuming, and require considerable operator skill. When coprecipitation methods are used to separate or preconcentrate trace constituents, the long manual procedures are particularly undesirable, as they may introduce contamination risks which are difficult to overcome. >espite the obvious drawbacks of the precipitation-dissolution manual batch procedure, little has been attempted for its automation, presumably owing to difficulties in designing efficient automated procedures for aging, quantitative transfer of precipitates on to a filter, and its subsequent dissolution or weighing [1]. 

It is useful to compare various sampling methods to quantitative chemical analysis and to list their respective advantages and limitations (Table 6.3). In fact, an analysis is only as good as the sample which has been introduced into the analytical instrument. The ideal way to carry out a quantitative analysis with a sampling technique is to transfer an analyte completely from the sample matrix to the analytical apparatus. This means that in principle quantitative analysis of an additive is well carried out by dissolution (100% recovery), especially when the procedure restricts additional handling (evaporation, preconcentration, redissolution, etc.). The routine application of )uSEC-GC is a case in point. For quantitative analysis, most instruments require a solution. On-line combinations of sample treatment and analytical systems are being studied intensively. The idea behind such systems is to perform sample extraction, clean-up and concentration as an integral part of the analysis in a closed system [14]. 

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