Salt matrix

Since NaCl is already a major constituent of the initial salt matrix, the complexity of the salt does not change. This is highly desirable from a reprocessing standpoint. 

The liquids used were 1 1 mixtures of EBA-HV and liquid methacrylate which also contained dihydroxyethyl-p-toluidine as the accelerator. Both mono- and di-methacrylates were used. The benzoyl peroxide initiator was included in the EBA zinc oxide/silanized (1 1) glass powder. These polymer cements set 5 to 10 minutes after mixing. Since there is a substantial amount of monomer in the liquid (50%) the contribution of the polymer to the strength of the cement must be considerable. Brauer Stansbury (1984b) suggested that the two matrices, the polymer matrix and the salt matrix, may be interpenetrating but separation of the two phases is likely. 

As cadmium is one of the most sensitive graphite furnace atomic absorption determinations, it is not surprising that this is the method of choice for the determination of cadmium in seawater. Earlier workers separated cadmium from the seawater salt matrix prior to analysis. Chelation and extraction [ 121— 128], ion exchange [113,124,125,129], and electrodeposition [130,131] have all been studied. 

In order to overcome the problem of the high nonspecific absorption, alternative procedures have been tested, which involve prior separation of the trace metals from the salt matrix. Examples of extraction of trace metals from seawater as chelates with subsequent determination by electrothermal atomic absorption spectrometric procedures have been described [381,382], but these and similar methods are seldom effective and satisfactory when the matrix is very complex and the analyte concentration very low. 

Graphite-furnace atomic absorption spectrometry, although element-selective and highly sensitive, is currently unable to directly determine manganese at the lower end of their reported concentration ranges in open ocean waters. Techniques that have been successfully employed in recent environmental investigations have thus used a preliminary step to concentrate the analyte and separate it from the salt matrix prior to determination by atomic absorption spectrometry. 

Nakahara and Chakrabarti [137] showed that the seawater salt matrix can be removed from the sample by selective volatilisation at 1700-1850 °C, but the presence of sodium chloride, sodium sulfate, and potassium chloride causes a considerable decrease in molybdenum absorbance, and magnesium chloride and calcium chloride cause a pronounced enhancement. The presence of magnesium chloride prevents the depressive effects. Samples of less than 50 pi can be analysed directly without using a background corrector with a precision of 10%. 

The considerable difficulty of trace element analysis in a high salt matrix such as seawater, estuarine water, or brine is clearly reflected in the literature. The extremely high concentrations of the alkali metals, alkaline earth metals, and... 

Many of the analytes of interest for solid phase chemical reference materials are the same as those in seawater, but the need for and the preparation of reference materials for suspended particulate matter and sediments is quite different. The low concentrations of many seawater species and the presence of the salt matrix create particular difficulties for seawater analyses. However while sediments frequently have higher component concentrations than seawater, they also have more complicated matrices that may require unique analytical methods. A number of particulate inorganic and organic materials are employed as paleoceano-graphic proxies, tracers of terrestrial and marine input to the sea, measures of carbon export from the surface waters to the deep sea, and tracers of food-web processes. Some of the most important analytes are discussed below as they relate to important oceanographic research questions. 

Table 3.4 Effect of KCI as a salt matrix on subtilisin Carlsberg and chymotrypsin in anhydrous hexanew [88].

Clearly there is much to be learned from further examination of arsenic levels in seawater and porewaters. However, low concentrations and analytical difficulties presented by the salt matrix continue to complicate these analyses (33, 85). Techniques such as HPLC/ICP-MS suffer from interference by the molecular ion 40Ar35Cl +, formed by combination of the plasma gas and chloride ion, with the monoisotopic 75As+. Techniques to separate the arsenic compounds from the salt matrix before HPLC/ICP-MS have not been fully investigated because they may result in fractionation of the compounds and loss of speciation information. Nevertheless, methods to establish the presence or otherwise in seawater of some of the arsenic-containing compounds important in other marine compartments is worth pursuing. 

Scientists at PNNL have developed an automated radiochemical sample preparation-separation-detection system for the determination of total "Tc in nuclear-waste process streams.46 85 86 144145 This analyzer was designed to support a technetium removal process planned as part of the development of a nuclear-waste processing plant. The process stream composition is both complex and variable, with a high pH, high salt matrix. Depending on the source of the feed, the total base content, the concentration of organics, and complexant concentrations will vary, as will the aluminum, nitrate, nitrite, dichromate, and radionuclide composition. 

The concentrations of trace elements in seawater varies geographically, spatially, and in depth [7j. Such variations are generally caused by the biological activities and physicochemical processes in the oceans. Thus, readers should note that the concentrations of trace elements given in Table 1 are not representative of those for all oceans. However, the extremely low levels of elements in concentrated salt matrix make accurate and precise analysis of seawater difficult. In recent interlaboratory investigations of seawater analysis by skillful marine or analytical chemists, a wide range of... 

Since DNA fragments from the PCR typically are contained in a high salt matrix, their mobility will vary depending on sample salt concentration. Thus, proper identification of these DNA fragments requires the use of an internal standard to normalize analyte velocity. This practice corrects for variance in fragment mobility due to sample matrix differences (i.e., salt content). These internal standards are included for size determination (in bp) as well as a reference for migration time. Candidates for such internal standards include the primer or primer-dimer peaks, since both components are already present in the PCR mixture alternatively, one or more coinjected standard DNA peak s may be chosen. If any of these fragments are to serve as the internal standard, they must be separated from one another and any PCR product, a precondition that is not easily met when the size of the PCR product is below 60 bp. 

Knifton has also shown (36 - 38,40) that nitrogen- or phosphorus-ligand modified ruthenium complexes, in a phosphonium salt matrix, can conveniently catalyze the hydroformylation of terminal alkenes with high selec-tivities in linear oxo products. Usually selectivities better than 80% were achieved. In the best case (160°C, 95 bar. CO/H2= 1/2) a linearity in nonanol of 94% was obtained starting from [Ru3(CO),2], 2,2 -bipyridine. and [PBu4]Br. The main products were alcohols and not aldehydes. However, it is often difficult to reduce the isomerization of oct-l-ene as well as its hydrogenation. The [Ru3(CO),2l/2,2 -bipyridine (bipy) system has been extensively explored. Two equilibria have been proposed to account for the infrared data and the effects of the bipy ligand [eqs. (8) and (9)]. 

Tungsten-coil atomizers have to some extent been used in connection with atomic techniques in general and ETA-AAS in particular, and their popularity continues to rise. Their high simplicity and low cost make them attractive alternatives to graphite furnaces for many applications. However, they are much more interference-prone than their graphite counterparts. The interferences experienced by W-coil atomizers have been overcome in various ways, however. Thus, Barbosa et al. [25] avoid the interference from a salt matrix and implement a preconcentration step by electrochemically reducing Pb onto the coil surface. They use a flow injection system to deliver the sample through an anode inserted in the tip of the autosampler and the W-coil itself as cathode. The use of a W-coil as a platform inside a Massmann-type furnace provides no appreciable improvement over wall atomization [26]. 

The sample passes through a 0.4-/xm Nuclepore (Pleasanton, Calif.) filter bag placed in a tubulated polyethylene container. The filter bags are made from 142-mm filters or, if a larger surface area is needed, by heat-sealing rectangles cut from 8X 10-in. Nuclepore filter sheets. A small bead of silicone rubber is applied to the filter holder cap to make the filter assembly leak-tight. The first Chelex column removes the trace metals from the seawater. The second Chelex column is used as an analytical blank to correct for any salt matrix effects from the first column. 

The product of this reaction appeared to have smaller particles than the original uranium dioxide, which settled rapidly to the bottom of the reaction tube. These particles were recovered by aqueous dissolution of the solidified eutectic and filtration of the insoluble uranium-containing species. No hydrolysis of the insoluble uranium-containing species is believed to occur with aqueous dissolution of the salt matrix. To preclude hydrolysis in experiments where it was more likely, the nitrate salts were dissolved in 0.5 M HNO3. 

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