Methods of Sample Preparation

Dissolving Inorganic Materials with Strong Acids 

The acids HCl, HBr, HF, H3PO4, and dilute H2SO4 dissolve most metals (M) by the reaction 

Many other inorganic substances also can be dissolved. Some anions react with to form volatile products (species that evaporate easily), which are lost from hot solutions in open vessels. Examples include carbonate (COi + 2H H2CO3 - C02(.i )t + H2O) and sulfide (S -I- 2H+ H2S( )t). Hot hydro-fluoric acid dissolves silicates found in most rocks. HF also attacks glass, so it is used in Teflon, polyethylene, silver, or platinum vessels. Teflon is inert to attack by most chemicals and can be used up to 260°C. 

Substances that do not dissolve in the acids above may dissolve as a result of oxidation by HNO3 or concentrated H2SO4. Nitric acid attacks most metals, but not Au and Pt, which dissolve in the 3 1 (vol vol) mixture of HCkHNOs called aqua regia. 

The mortar is the base and the pestle is the grinding tool. Agate is very hard and expensive. Less-expensive porcelain mortars are widely used, but they are somewhat porous and easily scratched. These properties can lead to contamination of the sample by porcelain particles or by traces of previous samples embedded in the porcelain. 

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Compatibility physieal influenee with tool ehemieal methods of sample preparation and the stage of determination based on any prineiple of an analytieal signal generation, the opportunity of automation of a sample preparation stage, eontrol, modeling of eonditions of analytieal proeess opens prospeets for their use in the analysis of food-stuffs, environment objeets, geologieal samples, ete. 

Two methods of sample preparation were investigated. The former is dilution of blood semm with 0.1% Triton X-100, the latter is aeid mierowave digestion. As evaluated, the most adequate mineralization proeedure for determining the majority of elements in blood semm by ICP AES is aeid mierowave digestion. However, the ICP AES determination of abundant elements (B, Si, Mn), whieh present in semm at 0.001-0.01 ppm levels should be follow sample dilution with Triton X-100. 

Determination of Na " and Na" ions in raw cosmetic materials was conducted with the developed method of flame photometry. A necessity of development of method of samples preparation arose up in the work process, as this spicily-aromatic raw material contained pectin in amount 0.1-0.5% and that prevented preparation of samples by standard method of extracts dilution and required incineration of analyzed sample, time of analysis was increased in 60 times. It was established that CaCl, solution with the concentration 0,4 % caused destmctions of the carbopol gel. It was established that the addition of 0,1% CaCl, and 0,1% NaCl salts solutions into the system intensified the effect of negative action of these salts onto the gel stmcture and the gel destmcted completely. 

The catalytic activity of the pure /3-palladium hydride has been studied under the appropriate temperature and pressure conditions. The palladium sample was converted into the hydride in a manner which bypassed the area of coexistence of the phases. This was achieved by suitably saturating the metal with hydrogen at 35 atm above the critical temperature and then subsequently cooling the sample to the required temperature and reducing the hydrogen pressure. This method of sample prepare tion allowed one to avoid cracking the palladium crystallites, which would... 

This equation predicts a value of 26.8%ofor the zebra at Turkana assuming an average value of 6%o for Lake Turkana water. This predicted value is l%o less than the actual value of 27.8%o. Given the variation in methods of sample preparation and analysis, variation between bone and tooth enamel (Stuart-Williams and Schwarcz 1997), and uncertainty in surface water oxygen isotopic composition, these values are extraordinarily close. Alternatively, if the equation is solved for using the actual value of the Turkana zebra. 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

The methods of sample preparation for AES are identical to those used in XPS (see Chapter 2.1), the objective again being to ensure that the surface to be analysed has not been contaminated or altered prior to analysis. AES must be carried out in UHV conditions. 

Pome Fruit Types. As with citrus fruit types, the method of sample preparation was modified for the parathion studies. In the earlier studies the DDT-treated apples and pears were scrubbed in a warm 10% solution of trisodium phosphate, and all the peel was removed from the water-rinsed fruit with a household-type potato peeler. The pooled samples of peel and pulp were then processed independently to recover the contained toxicant for subsequent estimation. 

The second method of sample preparation for IMS is a matrix-coating method for MALDI imaging. In this chapter, we review the choices of matrix compound and solvent composition appropriate for IMS of tissue sections. Three kinds of matrix-application methods and examples of their use are illustrated. 

To summarise, a fractionation step allows the isolation of the compounds of interest from the other molecular constituents, particularly from the fatty acids that are well-ionised. To compensate for the low ionisation yield of some compounds, such as TAGs, the solutions may be doped with a cation. Samples are then directly infused into the ion electrospray source of the mass spectrometer. A first spectrum provides an overview of the main molecular compounds present in the solution based on the peaks related to molecular cations. The MS/MS experiment is then performed to elucidate the structure of each high molecular compound. Table 4.2 shows the different methods of sample preparation and analysis of nonvolatile compounds as esters and TAGs from reference beeswax, animal fats and archaeological samples. 

Table 4.2 Summary of the different methods of sample preparation and analysis by direct ESI MS and ESI MS/MS...

Compound Method of sample preparation Herman and Weidinger s method Using internal standard IR Solution calorimetry Stability at 50°C and 31% RH Reference... 

The way the sample is filled in a holder affects the orientation of the crystallites. Numerous methods of sample preparation have been described in the literature [1], Morris et al. [61] avoided preferred orientation by using a sample holder in which the top face had a rectangular cavity that extended to one end of the holder. Building on that concept, an x-ray holder has been fabricated wherein the powder is filled from the side [49]. By using this holder, reproducible and reliable intensity measurements have been obtained [49,56]. 

The method employed will depend on the concentration of the element in the sample and on the matrix interferences. Methods of sample preparation have been reviewed 22). 

In our laboratories, a cycle time of 90 sec can be achieved with a dilution factor of 1 25 for a given sample concentration, allowing the purity and identity control of two and a half 384-well microtiter plates per day. The online dilution eliminated an external step in the workflow and reduced the risks of decomposition of samples in the solvent mixture (weakly acidic aqueous solvent) required for analysis. Mao et al.23 described an example in which parallel sample preparation reduced steps in the workflow. They described a 2-min cycle time for the analysis of nefazodone and its metabolites for pharmacokinetic studies. The cycle time included complete solid phase extraction of neat samples, chromatographic separation, and LC/MS/MS analysis. The method was fully validated and proved rugged for high-throughput analysis of more than 5000 human plasma samples. Many papers published about this topic describe different methods of sample preparation. Hyotylainen24 has written a recent review. 

One of the requirements of this approach is that the analytes must be stable at the boiling point of the solvent, since the analytes collect in the flask. The solvent must show high solubility for the analyte and none for the sample matrix. Since this is one of the oldest methods of sample preparation, there are hundreds of published methods for all kinds of analytes in as many matrices. For example, XAD-2 resin (sty-rene-divinylbenzene) that was used to collect air samples to monitor current usage of pesticides in Iowa was Soxhlet-extracted for 24 h with hexane/acetone [22], This is common in environmental sample analysis, and one will see rows and rows of these systems in environmental laboratories. One disadvantage of Soxhlet extraction is the amount of solvent consumed, though modern approaches to solid sample extraction have tried to reduce the amount of solvent used. 

PITC has been used extensively in the sequencing of peptides and proteins and reactions under alkaline conditions with both primary and secondary amino acids. The methods of sample preparation and derivatization follow a stringent procedure which involves many labour-intensive stages. However, the resulting phenylthio-carbamyl-amino acids (PTC-AA s) are very stable, and the timing of the derivatization step is not as critical as when using OPA. 

Namiesnik et al. [33] have reviewed the analysis of soils and sediments for organic contaminants. They discuss methods of sample preparation and isolation-preconcentration prior to instrumental determination. Compound classes discussed include volatile organic compounds, polychlorobiphenyls, polyaromatic compounds, pesticides and polychlorodibenzo-p-dioxins and polychlorodibenzofurans. 

An important criticism of the use of combustion trains is that combustion is not site specific, that is all atoms in the analyte end up in the gas transferred to the IRMS. For studies of carbon isotope effects this is invariably C02. The question is especially important for carbon isotope analysis because analyte molecules of interest usually contain several different kinds of carbon atoms and therefore combustion methods average or dilute the IE s of interest. Should site specific isotope ratios be required another method of sample preparation (usually much more tedious) is necessary. Combustion methods, however, are frequently used to study nitrogen and sulfur IE s because many organic molecules are singly substituted with these atoms. Obviously, oxygen isotope effects cannot be determined using combustion trains because external oxygen is employed. Rather some type of pyrolytic sample preparation is required. 

Smith RM. 2003. Before injection—modern methods of sample preparation for separation techniques. J Chromatogr A 1000 3. 

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