Semisolids, sampling

Studies designed to improve the determination of environmental contaminants will continue to provide refinements and improvements in the determination of acrylonitrile. The current high level of activity in supercritical fluid extraction of solid and semisolid samples should yield improved recoveries and sensitivities for the determination of acrylonitrile in solid wastes, and the compound should be amenable to supercritical fluid chromatographic analysis. Immunoassay analysis is another area of intense current activity from which substantial advances in the determination of acrylonitrile in environmental samples can be anticipated (Vanderlaan et al. 1988). 

Terms used, methods of sampling, and sample handling will be different for water and submerged solid and semisolid samples. The methods described earlier (i.e., transect and grid sampling) are also applicable to these situations. However, semisolid samples, such as those obtained from lake bottoms, require a special sampler. 

Semisolid samples. As with liquid samples, methods (B) and (C) are the best choices for this type of sample. The specific choice will depend on fhe rheological properties (viscosity, density, air retention) of the particular preparation. These samples are best measured in the transflectance mode. Liquid and semisolid samples may contain a mixture of solvents of disparate volatility which may evaporate separately during the measurement process. Differences in solvent volatility can alter the sample matrix and lead to errors in the determination which are best avoided by using a set of calibration samples spanning an expanded range of solvent proportions. ... 

For analyzing amphenicol residues in liquid samples such as milk, a pretreatment centrifugation step for fat removal is usually required (21, 22). Dilution of milk samples with water prior to solid-phase extraction cleanup is also often needed (23, 24). Semisolid samples such as muscle, kidney and liver, require, however, more intensive sample pretreatment. The most popular approach for tissue break-up is through use of a mincing and/or a homogenizing apparatus. 

For efficient extraction of macrolide and lincosamide residues from edible animal products, bound residues should be rendered soluble, most if not all of the proteins should be removed, and high recoveries for all analytes should be provided. Since tliese antibiotics do not strongly bind to proteins, many effective extraction methods have been reported. Sample extraction/deproteinization is usually accomplished by vortexing liquid samples or homogenizing semisolid samples with acetonitrile (136—139), acidified (136,140-142) orbasified acetonitrile (143), methanol (14, 144, 145), acidified (145-147) or basified methanol (148), chloroform (149-151), or dichloromethane under alkaline conditions (152). However, for extraction of sedecamycin, a neutral macrolide antibiotic, from swine tissues, use of ethyl acetate at acidic conditions has been suggested (153), while for lincomycin analysis in fish tissues, acidic buffer extraction followed by sodium tungstate deproteinization has been proposed (154). 

When analyzing milk samples for nitro furan residues, dilution with sodium chloride solution (155) or lyophilization (156) prior to extraction may be required. Dilution of egg samples with water prior to their solid-phase extraction has been also reported (157). Semisolid samples such as muscle, kidney, and liver, require a more intensive sample pretreatment. This involves use of a mincing apparatus followed by sample homogenization in water (37), sodium chloride solution (155), or dilute hydrochloric acid (158). 

Before the extraction procedure may commence, the sample must be prepared in such a way that it is in a condition for extraction of the analyte(s). For analyzing sulfonamide residues in liquid samples such as milk, a pretreatment dilution step with water prior to direct fluorometric detection may be required (207). Dilution of milk with aqueous buffer (208) or sodium chloride solution (209) prior to sample cleanup has also been reported. For the analysis of honey a simple dissolution of the sample in water (210, 211) or aqueous buffer (212) is generally required. Semisolid samples such as muscle, kidney, and liver, require, however, more intensive sample pretreatment. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. The most popular approach for tissue break-up is through use of a mincing and/or homogenizing apparatus. Lyophilization (freeze-drying) of swine kidney has been carried out prior to supercritical-fluid extraction of trimethoprim residues (213). 

Semisolid samples such as muscle, liver, and kidney normally require a more intensive sample pretreatment for tissue break-up. This is generally accom-... 

Extraction/deproteinization has been performed by either vortexing liquid samples or homogenizing semisolid samples with acetonitrile (227, 382, 383, 386-392), methanol (14, 393-395), methanol/water mixtures (396-401), ethyl acetate (384,402-406), dichloromethane (379,380,407), and acetone (408,409). Nonpolar organic solvents, such as isooctane (410, 411) and toluene (407), have also been reported to work extremely well for extracting salinomycin and dimetridazole from chicken tissues, respectively. Sample extraction with these nonpolar solvents yields a cleaner extract and an easier workup than extraction with commonly used polar solvents. However, selecting an extraction solvent is critical in establishing an analytical method because it is closely related to the cleanup systems. 

Semisolid samples such as muscle and liver tissues can be homogenized by blending with water or an appropriate aqueous solution such as a buffer in a mechanical or an ultrasonic device to expose the residue to the extraction solvent. Fatty tissue samples are sometimes subjected to heating at 40 or 60 C until fat becomes liquid, prior to extraction of the analytes with hexane (433) or acetonitrile (434), respectively. An alternative pretreatment approach is the enzymatic digestion of the tissue by means of proteolytic enzymes such as subtilisin A (429, 435-437). 

Liquid samples such as milk do not normally require application of any pretreatment procedure. Semisolid samples such as muscle, liver, and fat tissues usually require more intensive sample pretreatment for tissue break-up. The most popular approach is grinding the sample in a food chopper or homogenization in a Waring blender to expose residues to the extraction solvent. Fatty tissue samples are usually warmed at 35 C until fat melts (491-493), or sometimes blended with immersion blender (494). A fat sample that has been blended with immersion blender melts to produce yellow oil, whereas oil does not separate... 

Semisolid samples, such as kidney, liver, and muscle, often require more intensive sample pretreatment. A favorite approach for tissue break-up appears to be tire homogenization in acetonitrile (519, 523, 524) or in an acetone-sulfuric acid mixture (521). Using chloroform for extraction of xylazine and its main metabolite from kidney tissue, high recovery values were attained (525). However, prior alkaline hydrolysis of the incurred samples at 95 C was considered essential when diethyl ether was used for extraction of the -blocker carazolol and seven sedatives from kidney tissue (526). 

Extraction of different microcontaminants from a variety of semisolid samples... 

Sometimes, for solid and semisolid samples, the above-referenced methods were not suitable the extraction times were very long, with consequent chemical modifications and appearance of artifacts. Supercritical fluid extraction provides a good recovery of phenolics. The extraction behavior of phenolics has been delineated, using supercritical carbon dioxide and either sand or an inert support as sample matrix. ... 

The actual sampling procedure, whether manual or automated, is as follows (1) The fiber sheath pierces the septum of the sample vial. (2) The fiber is extended from the sheath into either liquid sample or the headspace above liquid, solid, or semisolid samples. (3) Equilibration of analytes between the fiber and liquid or headspace occurs over a period of time. (4) The fiber is withdrawn into its sheath. (5) The sheath is withdrawn from the vial and inserted into a hot or cold injection port of a gas chromatograph. (6) The sample desorbs into the carrier gas stream." Store opened, but unused, cartridges in a plastic bag in a desiccator. 

Thermal desorption (TD) is a technique in which solid or semisolid samples are heated under a flow of inert gas. Volatile and semivolatile organic compounds are extracted from the sample matrix into the gas stream and introduced into a gas chromatograph. Samples are typically weighed into a replaceable FIFE tube liner, which is inserted into a stainless steel tube for heating. 

In the analytical scheme, besides the sampling and the final analysis, the sample preparation and cleanup are also crucial. Sample preparation plays an important role in the analysis of FRs in environmental samples because of the complex matrices and only trace levels of analytes. Solid and semisolid samples are usually first dried and homogenized. Then the FRs are extracted from the sample (solid or liquid), and the extract is usually purified, fractionated, and concentrated before the final analysis, which is typically performed with gas or liquid chromatography. The extraction procedure is dependent on the sample matrix different methods are used for sediment, tissue, and liquid samples. After extraction, it will usually be necessary to purify and fractionate the extract, because most extraction methods are insufficiently selective and the separation power of the analytical technique not sufficient. Extracts typically contain several analytes similar to the FRs, which may be present in much higher quantities. The fractionation procedures are similar for the different types of extracts. Typical analytical procedures are given in Tables 31.2 to 31.6. 

Biochemistry, Clinical Chemistry, and Medicine Foods and beverages of many types have been analyzed by ICP-MS. Solid or semisolid samples are generally digested with mineral acid, as are some beverages. Peanut butter, commercial breakfast cereal, dried milk, fish and shellfish, wine, beer, and the like have been analyzed for trace elements such as Cu, Fe, Se, and Zn for nutritional purposes as well as for toxic metals like As and Pb. Al has been determined in many foods because dietary Al was being studied for a possible link to Alzheimer s disease. 

A recent development within membrane extraction for analytical purposes is its extension to also include solid samples. This provides a more simple way to work up such samples compared to currently prevailing techniques such as PLE. It also greatly simplifies measurements in semisolid samples (such as nondigested sewage sludge), which cannot be extracted with techniques for aqueous samples due to their large content of particulate matter but, on the other hand, require extensive dewatering by, for example, lyophilization if extracted by techniques for solid samples. 

The basic principle is that the solid or semisolid sample is suspended into an aqueous solution and left under stirring to reach equilibrium of the analyte between the solid particles and water. In some methods, the solid phase is then removed by centrifugation, while in others, it is kept in the sample during the extraction. " ... 

FIGURE 13.7 Setup for LPME of semisolid samples. The solid matrix is suspended in water the analytes will equilibrate between the solid particles and the aqueous donor phase. When the hoUow fiber is added, the analytes will be transported into the acceptor phase, thus driving the equilibrium between the solid particles and the donor solution toward desorption. 

Hgure 2 Miniaturized device for dynamic-PFE of solid and semisolid samples. (Reproduced with permission of Elsevier.)... 

The versatility of the design of an analytical pervaporation module, attributable to its changeable donor volume and the air gap present above the sample, has enabled its use with liquid, solid, and semisolid samples. Table 1 summarizes the applications of analytical pervaporation and the main fields in which it has been used. The manifold used and the way in which the sample is introduced in the system vary depending on whether it is liquid or solid. The main difference between the treatment of liquid and solid samples is the fact that with liquids the whole pervaporation process, from sample introduction to delivery of the results can be fully automated, while some operator s intervention is needed when dealing with solids. 

Trichlorotrifluoroethane-soluble floatable oil and grease Total solids dried at 103-105°C, total dissolved solids dried at 180°C, total suspended solids dried at 103-105°C, fixed and voiatiie solids ignited at 550°C, settleable solids (volumetric or gravimetric test) total, fixed, and volatile in solid and semisolid samples... 

Accelerated solvent extraction (ASE), also known as pressurized solvent extraction, is an instrumental technique that allows the extraction of solid or semisolid samples with organic solvents at temperatures above the boiling point of the solvent. In addition to the increased efficiency of... 

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