Sample decomposition

Ereeman, R. G. McCurdy, D. L. Using Microwave Sample Decomposition in Undergraduate Analytical Chemistry, ... 

Several common acid treatments for sample decomposition include the use of concentrated nitric acid, aqua regia, nitric—sulfuric acids, and nitric perchloric acids. Perchloric acid is an effective oxidant, but its use is ha2ardous and requkes great care. Addition of potassium chlorate with nitric acid also assists in dissolving any carbonaceous matter. 

Many analytical methods depend on the conversion of the tellurium in the sample to teUurous acid, H2Te02. Should teUurous acid precipitate on dilution, it can be redissolved with hydrochloric acid. Although tellurium is not as readily volatile as selenium, precautions should be taken to prevent the volatilisation of tellurium when halogen or hydrohaUde media are used during sample decomposition. 

There s it is required to keep unchangeable chemical forms of material components, as well as lanthanide concentration ratio in different degree of oxidation. Therefore, the main conception of this work is to combine process of the sample decomposition and analytical reaction of the determined chemical form. 

As the result of the performed investigations was offered to make direct photometric determination of Nd microgram quantities in the presence of 500-fold and 1100-fold quantities of Mo and Pb correspondingly. The rare earth determination procedure involves sample dissolution in HCI, molybdenum reduction to Mo (V) by hydrazine and lead and Mo (V) masking by EDTA. The maximal colour development of Nd-arsenazo III complex was obtained at pH 2,7-2,8. The optimal condition of Nd determination that was established permit to estimate Nd without separation in solution after sample decomposition. Relative standard deviations at determination of 5-20 p.g of Nd from 0,1 g PbMoO are 0,1-0,03. The received data allow to use the offered procedure for solving of wide circle of analytical problems. 

Sample decomposition is the critical operation in determination of total iodine in complex organic matrix. Iodine in simple form (I ) is highly volatile, so it should be transformed into nonvolatile analytical fomi (iodide or iodate) to prevent loses during the decomposition. 

The symptoms of column contamination include irregular peak shape, loss of resolution, loss of retention, irregular or noisy baseline, and ghost peaks from semivolatile materials of a previous run or from sample decomposition. Some of these problems can be the result of a contaminated injector. 

Following RM certificate instructions for material usage and handling, incorporate the RM into the scheme of analysis at the earliest stage possible, i.e. prior to the beginning of sample decomposition. Take it through the entire analytical procedure at the same time and under the identical conditions as the actual analytical samples in order to correctly monitor all the sample manipulation and measurement steps. 

Photo- decomposition High intensity sources may cause sample decomposition, which depends on the residence time of the sa le in the detector cell. 

During the LANA process, we observed the decomposition of 1,2/1,4 ketal (compound 2) in 2 hours in HPLC grade acetonitrile. A noticeable color change was observed. Since previous experience with sample decomposition led us to suspect that oxygen played a role in the decomposition reaction, a sample was prepared in acetonitrile with or without degassing. After 1 hour,... 

Decomposition methods are usually classified as melt decompositions, wet decompositions (with liquid decomposing agents) and dry decompositions by combustion. Sample decomposition methods are varied, and involve open and closed systems (at low and high pressure), UV and thermal activation, low or high temperature, and use of conventional convective or microwave heating. Table 8.4 lists the main sample decomposition methods for trace-element determination. 

Although it is extremely explosive, like other polyunsaturated azides, it was possible to run gaseous electron diffraction and IR spectra at cryogenic temperatures. Sample decomposition occurred during laser Raman spectral determination. 

The sample temperature was raised at a rate of 20°C/minute maintaining a nitrogen atmosphere. A considerable loss of weight, attributed to a loss of sorbed solvent (s. above), is observed below 130 °C. Sample decomposition obviously starts after melting. 

OV-1 on Gas Chrom Q as longer columns required a higher temperature to chromatograph neomycin and consequently had a reduced column life. A concentration of 3% OV-1 was preferred, as 2% or less resulted in increased column adsorption of neomycin. After a further study of the procedure Margosis and Tsuji238 recommended a number of improvements to optimise the analysis of neomycin by G.L.C. The improvements to the assay included the modification of the injection port to prevent sample decomposition by contact of injected material with... 

Observations are made concerning sample decomposition or explosion (e.g., a noisy report, smoke, or fire), cup deformation, and possible gas generation. 

In another study, thermodiffractometry was used to study phase transformations in mannitol and paracetamol, as well as the desolvation of lactose monohydrate and the dioxane solvatomorph of paracetamol [56]. The authors noted that in order to obtain the best data, the heating cycle must be sufficiently slow to permit the thermally induced reactions to reach completion. At the same time, the use of overly long cycle times can yield sample decomposition. In addition, the sample conditions are bound to differ relative to the conditions used for a differential scanning calorimetry analysis, so one should expect some differences in thermal profiles when comparing data from analogous studies. 

Table 4.2 gives a summary of methods for sample decomposition [36 K)]. Fluxes are particularly important for inorganic materials. The use of fluxes is limited by the reaction of trace elements within the crucibles and by the high blank levels in the fluxing materials themselves. 

Sample decomposition is not frequently automated because of difficulties caused by the long exposure times needed and the corrosive environments they produce. Hawk and Kingston [11] have described recent advances which make this preparative step more suitable for automation and particularly suited to robotic applications. 

The ultimate Q.C. protocol should anticipate the potential error sources in the whole analytical procedure. Destructive analyses that require extensive treatment for sample decomposition can lead to large analytical errors. Solid sample fusions and digestions should... 

The slowest step, which determines the speed of the entire analysis, is the sample decomposition step. Digestion of organic materials has generally taken the longest time of all sample types. Although it is true that most of these procedures could be made very efficient in batch operations, efforts to reduce preparation time by modification of procedures could prove invaluable to a routine laboratory(59). Some examples of this as applied to the analysis of bovine liver(60) and orange juice(61) can be found. 

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