Microwave-assisted dissolution

In this alternative, a 1-or 3-g sample aliquot is treated by microwave-assisted dissolution according to the method by Garcia and Kahn cited following this procedure. 

The determination of the main components in cement, such as Ca, with high precision is of importance, as is the determination of heavy metals such as thallium, however, because of environmental impacts. This can be performed successfully with AAS, provided the samples can be reliably brought into solution, as is now possible with microwave assisted dissolution. 

On-line procedures based on UV-photolysis or microwave-assisted dissolution have been established during recent years for the rapid digestion of relatively simple matrices such as water and waste water samples [130], [131 j. In 1124] on-line UV digestion with a segmented-flow device was applied for the determination of total cyanide prior to amperometric detection. The detection limit was found to be 0.2 pg/L. The throughput is about 30 analyses per hour. 

Metals analysis in particular should be mentioned in the field of industrial products. Apart from solution analysis, direct metal analysis by spark ablation is also very useful [109]. Through the availability of CCD spectrometers, the analytical precision that can be achieved is so high that even for major components errors as low as or even lower than in classical chemical methods can be achieved. This is documented by the analysis results for stoichiometric determinations of high-temperature superconductors of the Y-Ba-Cu-O type (Fig. 110) [456]. It also applies for ceramics of the Si-B-N-C type, where sample decomposition by various methods including microwave-assisted dissolution, dissolution by fusion, and... 

Coedo, A. G., Dorado, M.T., Padilla, I., and Alguacil, F.J. (1998). Use ofboric acid to improve the microwave-assisted dissolution process to determine fluoride forming elements in steels by flow injection inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 13(10), 1193. 

S, Soxhlet S , Soxtec R, reflux SF, shake-flask US, ultrasonics SFE, supercritical fluid extraction MAE, microwave-assisted extraction PFE, pressurised fluid extraction (ASE , ESE ) D/P, dissolution/precipitation. 

Methods involve extractions of analytes into organic solvents, as well as treatments with acidic or basic reagents. Solid-phase extraction can be used for removal and pre-concentrations of analytes in aqueous solutions. Applications of low-power focused microwave technology have been investigated as a means of dissolution, and good results have been reported for extractions of organometal-lic compounds of tin and mercury (Schmitt et al., 1996 Szpunar et al., 1996). Analyses of CRMs were used for verification. The time necessary for quantitative isolations of the analytes was greatly reduced, e.g. 24 h to 5 min. In addition, there were reductions in solvent volumes, and improvement in analyte recoveries. Some of the analytical procedures for speciation of particular elements such as mercury, described later in this chapter, include microwave-assisted sample preparation. 

Step 4a. For microwave-assisted, digestion, follow the procedure developed for the microwave system in the laboratory. Note that total dissolution of the solid is required for radioanalytical chemistry, whereas partial dissolution is acceptable for other analytical processes if the method has been tested for fractional recovery. Several references are given below that may be helpful in developing or using this method. 

Depending on the complexity of the sample matrix, a pre-cleaning step is a possible solution to remove interfering eflFects nevertheless, the choice should be a good compromise in relation to the total time and cost of analysis [33]. Supercritical fluid- [48,49], microwave-assisted- [50] or solid-phase extraction (SPE) [51-53] have been used as pre-cleaning steps prior to immunoassay. However, in certain situations, the extraction step led to a decrease in accuracy and recovery, probably due to analyte loss during clean-up/ evaporation/re-dissolution steps [53]. 

Although some authors have used microwaves as an auxiliary form of energy in HS — the ensuing methods being labelled microwave-assisted purge and trap — microwaves are in fact used in a preliminary, separate sample dissolution step that is followed by cooling and insertion of the sample into the HS module [54]. 

Twelve vials of the candidate CRM were distributed to each participant in the certification project. All laboratories were free to use the instrumental approach with which they felt more confident and to pretreat the specimens as necessary to adequately present them to the technique of choice. Table 10.4 lists the participants in this project and the techniques used. For the analysis, laboratories were requested to perform complete and independent dissolutions (for techniques requiring the presentation of samples in the liquid form) of the mass contained in five vials (five independent analytical runs, three replicates each). Digestions were to be carried out on different days for each sample. The dissolution of krill was achieved mostly by microwave-assisted acid digestion. 

In many cases, however, the costs arising from sample preparation will become decisive, which favors x-ray spectrometric methods, provided the earlier mentioned limitations are not encountered. Future progress will certainly depend on the avail-abilty of on-line sample treatment using, for example, flow injection and eventually on-line sample dissolution as is possible in some cases with microwave-assisted heating. Also the realization of separations in miniaturized systems and with minute amounts of reagents is very promising. In each instance the question of which method should be selected will have to be discussed for each type of analytical task to be solved. 

Blood, Microwave-assisted oj gen ashing, dissolution Microwave induced emis- Van Montfort... 

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