Sample dissolution selective

For the analysis of organic additives in polymeric materials, in most cases, prior extraction will be necessary. Depending on the nature of the additive, many different approaches are employed. These include soxhlet extraction with organic solvent or aqueous media, total sample dissolution followed by selective precipitation of the polymer leaving the additive in solution, assisted extraction using pressurised systems, ultrasonic agitation and the use of supercritical fluids. In trace analysis, solid phase extraction (SPME) from solution or solvent partition may be required to increase the analyte concentration. 

Extraction is the selective dissolution, as opposed to total sample dissolution, of the analyte from a sample. The sample can be either a solid material or a liquid, such as a water solution. 

The importance of the total sample dissolution technique mentioned earlier becomes apparent because the detrital phase contains Th and U that is both lattice-bound and adsorbed but in unknown proportions. Bischoff and Fitzpatrick (1991) demonstrated that it is not possible to quantitatively separate these two components by selective leaching. 

Sample dissolution is probably one of the most common operations in analytical chemistry and is carried out by dissolving in a suitable solvent to a suitable concentration that the analyte of interest can be reproducibly measured. If the composition of the non-aqueous solution is amenable to combustion in a flame or plasma, direct aspiration is possible. Unfortunately, ICP-AES instruments do not have the same solvent tolerance as AAS and require that the solvent selected be stable, non-quenching and non-interfering. Calibration standards are usually prepared in the same metal-free solvent, keeping in mind the effect of sample in the solvent. If the nebulisation efficiency of sample/solvent mixture is different to standards prepared in the same solvent only, then corrective actions must be taken so this anomaly can be taken into consideration. 

The concentration of metals that are detrimental to catalysts added can vary between 20.0 ppm for Fe to 100 ppm for Ni and lOOOppm for V. The presence of these metals necessitates the need for analysis of these metals to determine their concentrations prior to the cracking process. The best method to analyse these oil samples needs to be rapid and accurate. Careful selection of the method either from experience or by trial and error may be applied depending on the metal and the concentration. Sample dissolution in a solvent or solvent mixture is considered the easiest but may not be suitable for low limits of detection. Destructive sample preparation methods, i.e. oxygen bomb combustion, microwave acid digestion followed by pre-concentrating may be required for trace analysis and/or with the aid of a hyphenated system, e.g. ultrasonic nebuliser. Samples prepared by destmctive methods are dissolved in aqueous solutions that have very low matrix and spectral interferences. 

The reasons for postponing a discussion of the preliminary steps to this point are pedagogical. Experience has shown that it is easier to introduce students to analytical techniques by having them first perform measurements on simple materials for which no method selection is required and for which problems with sampling,. sample preparation, and. sample dissolution are either nonexistent or easily solved. Thus, we have been largely concerned so far with measuring the concentration of analytes in simple aqueous solutions that have few inteifering. species. 

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. 

Sample introduction and sample pretreatment are still limiting factors in AAS, determining the selectivity and sensitivity of the AA analysis. In AAS, typically liquid samples are analyzed. Nevertheless, several sample introduction systems have been developed for the direct atomic absorption analysis of solid samples avoiding sample dissolution, which is labor intensive and suffers risks of both contamination and losses. Solid samples in the form of powders, slurries, etc., are mostly analyzed in electrothermal atomizers. 

See also Atomic Absorption Spectrometry Principles and Instrumentation. Atomic Emission Spectrometry Principles and Instrumentation. Elemental Speciation Overview. Food and Nutritional Analysis Sample Preparation. Ion-Selective Electrodes Overview. Quality Assurance Reference Materials. Sample Dissolution for Elemental Analysis Dry Ashing Oxygen Flask Combustion Wet Digestion Microwave Digestion. Spectrophotometry Inorganic Compounds. Titrimetry ... 

Many techniques employed for elemental analysis require the conversion of the sample matrix into a solution form. The selection of an appropriate treatment for sample dissolution depends on the nature of the sample, and different approaches are required for predominantly inorganic and predominantly organic matrices. Geological, geochemical, and soil samples generally contain silicate, metal oxides, carbonates, and, in many cases, organic matter. Such samples must be dried and ground to a fine powder to... 

In contrast, the application of solution nebulization in conjunction with MC-ICP-MS now readily rivals or even surpasses the importance of TIMS for isotopic analysis of metallic and metalloid elements in bulk meteorite samples. Invariably, such analyses encompass (i) sample dissolution, most often by add digestion, and (ii) a highly selective separation of the analyte element from the bulk sample matrix, typically by one or several stages of column chromatography. Such separations are carried out prior to isotopic analysis of both major elements (e.g.. Mg, Si, Fe) and trace constituents, primarily to ensure that spectral interferences and matrix effects are reduced to either insignificant or at least tolerable levels. In addition, the chemical isolation procedure also acts as a preconcentration method, which allows the isotopic analysis to be carried using solutions that feature element concentrations that are optimized for precise data acquisition. 

On the basis of IR and Raman spectroscopy (Table 5.2, Figure 5.12), which are relatively cheap, fast, and easy for technical operation and interpretation of data, and do not require sample dissolution methods, we presented the quantitative determination of the six binary mixtures with the studied cephalosporins in solid state, which was reported for the first time in the literature. The IR-LD analysis of oriented colloids as a liquid crystal suspension was applied for experimental IR band assignment and selection of appropriate bands for quantitative determination. This method gives additional supramolecular solid-state structural information at room temperature and atmospheric pressure. It also avoids the phase transition and guarantees the study of different forms without polymorph transitions. This approach has been applied recently for caffeine as a matrix compound and for studying the polymorphs of Paracetamol, Aspirin, Phenacetin , and Salophen. The spectroscopic data were... 

Vacuum sublimation is a very popular method for purification of organometallic compounds, because it is so convenient and easy. The sublimation process is not very selective, however, so that it is seldom possible to separate cleanly more than one or perhaps two compounds from a mixture, while in many cases several compoimds occur simultaneously in the irradiated targets. Moreover, annealing may be induced by the heating of the sample for sublimation, although this can be minimized by prior dissolution of the sample to release reactive atoms and... 

It is also possible that the last step may occur during dissolution just before separation, or in the solid as the sample is warmed up to room temperature. The first of these can, in fortunate cases, be intercepted, so as to form a selected compound from a radical or other incomplete molecule in the solid (46). There are several examples of the second—room-temperature annealing—and it is useful when possible to dissolve the target at low temperature. 

SFE has been used extensively in the analysis of solid polymers. Supercritical fluid extraction of liquid samples is undertaken less widely because dissolution or entrainment of the matrix can occur. As illustrated elsewhere SFE has also been applied for the analysis of liquid poly(alkylene glycol) (PAG) lubricants and sorbitan ester formulations [370]. The analysis of PAG additives (antioxidants, biocides and anticorrosion, antiwear and antifoaming agents) is hindered by the presence of the low molecular weight PAG matrix (liquid) and therefore a method for the selective separation of additives from PAG is required. The PAG... 

The polymer/additive system in combination with the proposed extraction technique determines the preferred solvent. In ASE the solvent must swell but not dissolve the polymer, whereas MAE requires a high dielectric solvent or solvent component. This makes solvent selection for MAE more problematical than for ASE . Therefore, MAE may be the preferred method for a plant laboratory analysing large numbers of similar samples (e.g. nonpolar or polar additives in polyolefins [210]). At variance to ASE , in MAE dissolution of the polymer will not block any transfer lines. Complete dissolution of the sample leads to rapid extractions, the polymer precipitating when the solvent cools. However, partial dissolution and softening of the polymer will result in agglomeration of particles and a reduction in extraction rate. 

Your primary concern when selecting a solvent should be the complete dissolution of your sample. Again, this might seem an unduly trivial observation, but if your sample is not in solution, then it... 

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