Samples, for extraction

This technique can be also applied when the water-miscible acetonitrile is added to the serum sample for extracting the analytes. Following the addition of acetonitrile, the solution is saturated with potassium chloride so that the water and acetonitrile phases separate and derivatization is performed in the acetonitrile layer. Such alkylating procedures have been applied for prechromatographic derivatization of various drug residues with carboxylic groups, including penicillins (252) and barbiturates (253). 

Stir-bar sorptive extraction (SBSE) is carried out using a commercially available glass stir bar (Twister, from Gerstel GmbH) coated with polydimethylsiloxane (PDMS). A special thermal desorption unit is necessary to introduce the extract into a GC. It can be applied to headspace extraction, but is intended for stirring liquid samples for extraction. The same coatings used for SPME can be used for SBSE, and thus similar selectivity should be observed. 

The operational performance of an HF-based ESTM technique was first described by Liu et al.71 A 15-cm piece of HF was filled with an acceptor buffer solution, after which the F1F was made into a loop. This loop-like F1F device was soaked in n-undecane, and then immersed in 1 L of a river or leachate water sample for extraction of freely dissolved chlorophenols. This FIF-loop device was also employed for selective ESTM sampling of freely available Cu+2 in leachate water.78 The selectivity stemmed from a selective liquid membrane (di-n-dihexyl ether) containing a carrier (crown ether/oleic acid) and a selective stripping agent in the acceptor solution. 

Bermuda Deep Sea Profile. Monaghan et al, (9) discuss a vertical profile of the water column (surface to bottom, 4500 m) obtained west of the Berumuda Islands using the chartered R/V Panularis. Sampling for extractable organics and nonvolatile hydrocarbons consisted of 13 casts of three 30-1. Niskin bottles. The casts were arranged so that the... 

The use of immunoassays in the field of agricultural research has increased dramatically in recent years, and has become a reliable analytical tool that possesses numerous advantages over standard, chemical extraction and analytical methods. A few Of these advantages (described in several review articles (1,2)), include its greater sensitivity and specificity, the increased speed of the assay, which allows greater sample thrdugh-put, the requirement for smaller samples for extraction, and the assay s improved cost effectiveness. Enzyme-linked immunosorbent assays (ELISA) have been... 

The tissue sample for extraction is weighed wet after it has been broken... 

Waste can be a very complex matrix, which produces not only liquid and solid samples, but also multiphase samples. The critical step when dealing with waste is preparing multiphase samples for extraction. Extraction, clean-up, and analytical methods are, otherwise, similar to those used for soils, except that pollutant concentrations can be very high. 

Nail analysis has not been widely utilized in forensic toxicology, but some methods have been reported using GC (124). Nail samples receive similar treatment to hair samples for extraction of the drug. 

Extraction Between Two Phases When the sample is initially present in one of the phases, the separation is known as an extraction. In a simple extraction the sample is extracted one or more times with portions of the second phase. Simple extractions are particularly useful for separations in which only one component has a favorable distribution ratio. Several important separation techniques are based on simple extractions, including liquid-liquid, liquid-solid, solid-liquid, and gas-solid extractions. 

The following experiments introduce students to the importance of sample preparation and methods for extracting analytes from their matrix. Each experiment includes a brief description of the sample and analyte, as well as the method of analysis used to measure the analyte s concentration. 

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

Furthermore, the extent to which we can effect a separation depends on the distribution ratio of each species in the sample. To separate an analyte from its matrix, its distribution ratio must be significantly greater than that for all other components in the matrix. When the analyte s distribution ratio is similar to that of another species, then a separation becomes impossible. For example, let s assume that an analyte. A, and a matrix interferent, I, have distribution ratios of 5 and 0.5, respectively. In an attempt to separate the analyte from its matrix, a simple liquid-liquid extraction is carried out using equal volumes of sample and a suitable extraction solvent. Following the treatment outlined in Chapter 7, it is easy to show that a single extraction removes approximately 83% of the analyte and 33% of the interferent. Although it is possible to remove 99% of A with three extractions, 70% of I is also removed. In fact, there is no practical combination of number of extractions or volume ratio of sample and extracting phases that produce an acceptable separation of the analyte and interferent by a simple liquid-liquid extraction. 

This somewhat lengthy experiment provides a thorough introduction to the use of GG for the analysis of trace-level environmental pollutants. Sediment samples are extracted by sonicating with 3 X 100-mL portions of 1 1 acetone hexane. The extracts are then filtered and concentrated before bringing to a final volume of 10 mL. Samples are analyzed with a capillary column using a stationary phase of 5% phenylmethyl silicone, a splitless injection, and an EGD detector. 

One of our previous complaints was that we had more parameters than we knew what to do with Eq. (2.33) makes this problem even worse. It turns out, however, that using only two or three terms of Eq. (2.33) results in a usable equation with improved curve-fitting ability. Techniques have been developed for extracting acceptable parameters from experimental data in these cases (see Problem 4). Figure 2.9, for example, shows data collected from a sample of natural rubber, analyzed according to a two-term version of Eq. (2.33). The line in Fig. 2.9 is drawn according to the equation... 

Preparation of soil—sediment of water samples for herbicide analysis generally has consisted of solvent extraction of the sample, followed by cleanup of the extract through Uquid—Uquid or column chromatography, and finally, concentration through evaporation (285). This complex but necessary series of procedures is time-consuming and is responsible for the high cost of herbicide analyses. The advent of soUd-phase extraction techniques in which the sample is simultaneously cleaned up and concentrated has condensed these steps and thus gready simplified sample preparation (286). 

Cutter-type samplers can be installed for low pressure pipelines and enclosed troughs. These samplers contain a movable cutter coimected to a flexible hose through which the sample is extracted. Such devices meet all three rules for good sampling they sample a moving stream, the sample is made... 

Supercritical CO2 has also beea tested as a solveat for the removal of organic contaminants from sod. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlotinated biphenyls (PCBs), may be removed from sod samples (77). Supercritical CO2 can also extract from sod the foUowiag hydrocarbons, polyaromatic hydrocarbons, chlotinated hydrocarbons, phenols, chlotinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

Removing an analyte from a matrix using supercritical fluid extraction (SEE) requires knowledge about the solubiUty of the solute, the rate of transfer of the solute from the soHd to the solvent phase, and interaction of the solvent phase with the matrix (36). These factors collectively control the effectiveness of the SEE process, if not of the extraction process in general. The range of samples for which SEE has been appHed continues to broaden. Apphcations have been in the environment, food, and polymers (37). 

The development of methods of analysis of tria2ines and thek hydroxy metabohtes in humic soil samples with combined chromatographic and ms techniques has been described (78). A two-way approach was used for separating interfering humic substances and for performing stmctural elucidation of the herbicide traces. Humic samples were extracted by supercritical fluid extraction and analy2ed by both hplc/particle beam ms and a new ms/ms method. The new ms /ms unit was of the tandem sector field-time-of-flight/ms type. 

For most assays, the incorporated pantothenic acid has to be Hberated en2ymatically. Usually, a combination of pantotheinase and alkaline phosphatase is used to hberate the bound pantothenic acid. The official method for pantothenic acid of the Association of Official Analytical Chemists (AOAC) is the microbiological assay that uses U. Plantarium (A.TCC 8014) as the test organism (71). Samples are extracted at 121°C at pH 5.6—5.7, proteins are precipitated at pH 4.5, and the resulting clear extracts are adjusted to pH 6.8 prior to assay. This procedure is only suitable to determine calcium pantothenate or other free forms of pantothenic acid. 

Analytical Supercritical Fluid Extraction and Chromatography Supercritical fluids, especially CO9, are used widely to extrac t a wide variety of solid and hquid matrices to obtain samples for analysis. Benefits compared with conventional Soxhlet extraction include minimization of solvent waste, faster extraction, tunabihty of solvent strength, and simple solvent removal with minimal solvent contamination in the sample. Compared with high-performance liquid chromatography, the number of theoretical stages is higher in... 

The instrumental analyzer procedure, EPA Method 3A, is commonly used for the determination of oxygen and carbon dioxide concentrations in emissions from stationary sources. An integrated continuous gas sample is extracted from the test location and a portion of the sample is conveyed to one or more instrumental analyzers for determination of O9 and CO9 gas concentrations (see Fig. 25-30). The sample gas is conditioned prior to introduction to the gas analyzer by removing particulate matter and moisture. Sampling is conducted at a constant rate for the entire test run. Performance specifications and test procedures are provided in the method to ensure reliable data. 

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