Extraction techniques , Sample preparation

Because preparation involves specialized procedures and instruments, most of analytical laboratories have Sample Preparation Sections, such as Organic Extraction and Metal Digestion shown in Figure 4.2. (The General Chemistry Section does not have a separate preparation group, as sample preparation is usually part of the analytical procedure). Because laboratory accuracy and precision strongly depend on the individual s technique, sample preparation personnel must be trained in each procedure, and their proficiency be documented. The laboratory must have a set of SOPs for preparation methods performed and must ensure that the Sample Preparation Group personnel are trained to follow them to the letter. 

Mass spectrometry (MS), infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy with their numerous applications are the main instrumental techniques for the detection and identification of CWC-related chemicals. During the last few years, however, less laborious techniques such as liquid chromatography (LC) and capillary electrophoresis (CE) have become attractive for the analysis of water samples and extracts where sample preparation is either not required or is relatively simple. 

Solid phase extraction. A sample preparation technique using liquid-solid sorption to remove contaminants from the sample or isolate the sought for compounds from the sample. 

Analyses were carried out under repeatability conditions, that is in the same laboratory, by the same operator, applying the same instrumentation and analytical method on the same day, except for RM15 where, due to the extraction process, sample preparation was performed by two operators and samples were analysed on different days. In all cases, upon arrival in the laboratory, the samples were stored at 4°C before processing. Quantification was performed by external calibration graphs, using internal standards when ICP-MS and GC-MS were the analytical techniques. 

Dixit, V. and Dixit, V. M. 1990. A solid-phase extraction technique for preparation of drugs-of-abuse samples Am. Lab., May/June, 47-51. 

Meissner G, Hartonen K, Riekkola LL. Supercritical-fluid extraction combined with solid-phase extraction as sample preparation technique for the analysis of beta-blockers in resum and urine. Fresenius J Anal Chem 1998 360 618-621. 

Solid phase extraction (SPE) techniques are emerging as the perhaps most popular alternatives to liquid-liquid extraction for sample preparation of food and agricultural samples. The principle of SPE is now fully described (9,10). Most sorbents are now available as disks, cartridges or precoiumns (11,12). Among the advantages of SPE, is die easiness for the method to be automated and the possibility for simultaneous combination of extraction and enrichment of the analytes (12). This reduces the whole analytical scheme compared to liquid-... 

It would be most desirable to study lipid oxidation in intact food products without the extraction or sample preparation steps currently necessary (e.g., pelletization, freeze-drying). Perhaps improvements in techniques such as the Fourier transform infrared photoacoustic spectroscopy (Yang and Irudayaraj, 2000) will open such possibilities. 

Supercritical fluid extraction (SEE) using supercritical carbon dioxide (SC-CO2) has been successfully used for isolation of volatile nitrosamines from different matrices such as tobacco and food products. This technique presents several advantages with respect to other extraction methods (e.g., mineral oil distillation or low-temperature vacuum distillation) currently used. Thus, SEE minimizes sample handling, provides fairly clean extracts, expedites sample preparation, and reduces the use of environmentally toxic solvents. Good results have also been obtained with the use of SPE in the analysis of food matrices combining extraction with Extrelut sorbent and purification with Florisil. This method is applicable for the analysis of a range of the most widely encountered volatile N-nitrosamines, including the poorly volatile NDBA, NDBzA, and N-nitroso-N-methylaniline in various food products. Active carbon is suitable for this preconcentration step due its low cost, versatility, and easy application. 

Before any sample can be subjected to chromatography, some type of sample preparation is required, which can be as simple as filtration or an involved solid-phase extraction protocol. Sample preparation is that activity or those activities necessary to prepare a sample for analysis. The ultimate goal of sample preparation is to provide the component of interest in solution, free from interferences, and at a concentration appropriate for detection. Sample preparation can be divided into a number of classes of activities solvent extraction, sorbent extraction and compound isolation, headspace, and membrane separations, with each of these areas further divided into techniques that apply to the category of activities. 

A ricin detection method has been developed that couples LC-MS/MS with an enzyme-linked immunosorbent assay (ELISA).The analyte target for MS detection is adenine, which is released from ricin during the assay. Adenine detection limits were achieved at 0.1 ng/mL or 1.56 pM in a 500-pL sample volume with this method. This LC-MS method may be chosen over other techniques because milk and drinking water are the intended real-world application for this protocol [77]. Another MS/MS technique detects tryptic peptide fragments from ricin produced by an immunoassay technique. This technique utilizes the inherent speed of MS analysis to confirm peptide identity. This technique is applied to the detection of ricin in food and body fluids such as blood serum and saliva [78]. A similar LC-MS/MS method uses an organic solvent-assisted tryptic digest to prepare samples of crude ricin extracts. This sample preparation... 

Extraction A sample preparation technique that removes the analyte from the matrix. 

Micellar solutions of cationic surfactants have been widely employed in separation science in spectroscopic methods [2], in extraction-preconcentration sample preparation schemes [3], in chromatographic techniques, etc., mainly as convenient substitutes of toxic conventional organic solvents. 

As numerous examples in this book illustrate, SPME is a potent sample preparation tool for the analysis of odor- and flavor-impact chemicals and is capable of providing results equivalent to or better than conventional extraction techniques. SPME is a deceptively simple technique. It is a fast and simple sample preparation method, and sample chromatograms can be generated quickly. However, quantitative accuracy with SPME is highly dependent on experimental conditions, sample matrix, analyte characteristics, the type of fiber, and calibration techniques. SPME, more so than other extraction/concentration sample preparation techniques, is an evolving technology because new fibers are constantly being introduced. 

SPME, like all extraction/concentration sample preparation techniques, has strengths, weaknesses, and biases. Understanding what they are and how to control them allows users to maximize the effectiveness of SPME as a tool for the analysis of flavors, fragrances, and odors. 

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). 

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

Although SFE and SFC share several common features, including the use of a superaitical fluid as the solvent and similar instrumentation, their goals are quite distinct. While SFE is used mainly for the sample preparation step (extraction), SFC is employed to isolate (chr-omatography) individual compounds present in complex samples (11 -15). Both techniques can be used in two different approaches off-line, in which the analytes and the solvent are either vented after analysis (SFC) or collected (SFE), or on-line coupled with a second technique, thus providing a multidimensional approach. Off-line methods are slow and susceptible to solute losses and contamination the on-line coupled system makes possible a deaease in the detection limits, with an improvement in quantification, while the use of valves for automation results in faster and more reproducible analyses (16). The off-line... 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

Although on-line sample preparation cannot be regarded as being traditional multidimensional chromatography, the principles of the latter have been employed in the development of many on-line sample preparation techniques, including supercritical fluid extraction (SFE)-GC, SPME, thermal desorption and other on-line extraction methods. As with multidimensional chromatography, the principle is to obtain a portion of the required selectivity by using an additional separation device prior to the main analytical column. 

Sample preparation will involve extraction techniques, concentration procedures and methods for removing solid contaminants that may damage the sample valve, column or some other part of the... 

The two examples of sample preparation for the analysis of trace material in liquid matrixes are typical of those met in the analytical laboratory. They are dealt with in two quite different ways one uses the now well established cartridge extraction technique which is the most common the other uses a unique type of stationary phase which separates simultaneously on two different principles. Firstly, due to its design it can exclude large molecules from the interacting surface secondly, small molecules that can penetrate to the retentive surface can be separated by dispersive interactions. The two examples given will be the determination of trimethoprim in blood serum and the determination of herbicides in pond water. 

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