Sample treatment and extraction

In analytical work on speciation, methods of wet sample preparation are very important parts of the overall scheme of analysis. Constraints on preparation methods include low concentrations of analytes, often less than 0.1 mgg-1, stabilities of the analytes, and the need for suitable solutions for instrumental techniques of elemental determinations. Volume of sample and type of matrix must be considered. Procedures for the quantitative recoveries of organometallic compounds from sediments and organic matrices can be time-consuming. Their efficiencies and reliabilities must be thoroughly tested for each type of sample for analysis. 

Methods involve extractions of analytes into organic solvents, as well as treatments with acidic or basic reagents. Solid-phase extraction can be used for removal and pre-concentrations of analytes in aqueous solutions. Applications of low-power focused microwave technology have been investigated as a means of dissolution, and good results have been reported for extractions of organometal-lic compounds of tin and mercury (Schmitt et al., 1996 Szpunar et al., 1996). Analyses of CRMs were used for verification. The time necessary for quantitative isolations of the analytes was greatly reduced, e.g. 24 h to 5 min. In addition, there were reductions in solvent volumes, and improvement in analyte recoveries. Some of the analytical procedures for speciation of particular elements such as mercury, described later in this chapter, include microwave-assisted sample preparation. 

Supercritical fluid extraction (SFE) procedures have been developed for extractions of species of elements from samples. Viscosities and diffusion coefficients 

Sequential extraction procedures have been applied for the purpose of isolating species of elements from particulate materials, soils and sediments (see Chapters 10 and 11). In sequential extraction procedures, samples are treated with a series of chemicals under rigorously controlled conditions of temperature, time and ratio of reactant to sample. The work of Tessier et al. (1979) resulted in a carefully designed procedure for the determination of species of elements in sediments. It has been used and modified by other investigators. Trace elements in the extracts are usually determined by means of AAS, ICPAES and ICP-MS. An example is the study of sequential extractions for the determination of 20 trace elements in ten certified geological reference materials (Hall et al., 1996). 

Some of these fractionation problems can be ameliorated by the use of the relatively new technique of field-flow-fractionation (FFF). Its advantages include high-resolution separation and sizing of particulate, colloidal and macromolecu-lar materials covering 105-fold range from about 10 3 to 1()2/rm (see Chapter 8). 

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Main methodologies for sample treatment and extraction for the analysis of PFAS in food and biota are summarised in Table 1. Main sample preparation and extraction procedures have been based on ... 

There have been concerns, within the coloration industry, regarding the actual analytical test procedures, since false positives (a result indicating a banned amine is present when the original colorant was not based on any banned amines) have been obtained with some colorants under the rather harsh sample treatment and extraction processes employed. The cunent official methods published do not use such harsh conditions. Perhaps the real winners in all of this are the contract analytical labs who do all the testing (and possibly the consumers to some extent) Further details about the analysis of these species are contained in Section 10.6 on separation science. 

The application of solution phase electrochemistry for studying the work of art samples and archaeological artifacts requires, as previously indicated, sample treatment via extraction or chemical attack. This is an obvious drawback, because these operations, apart from the requirement of relatively high amounts of sample, usually lead to a loss of information since the solid is dissolved and all signals that are specific for the solid compound or material are not available anymore for measurements. 

Preparation of Coal and Fly Ash for Isotope Dilution Analysis. Separate aliquots of coal and fly ash are weighed out and spiked with 204Pb and 233U, respectively. The chemical treatment and extraction of lead and uranium from coal and fly ash are identical, except coal is ashed at 450 °C before chemical treatment. The samples are dissolved with a mixture of hydrofluoric, nitric, and perchloric acids in Teflon beakers. The lead is separated by dithizone extraction, evaporated to dryness, redissolved in dilute nitric acid, and 10 ng are loaded on filaments with silica gel for mass analysis. 

The Prelude" Workstation, which is capable of automating solid sample treatments and includes options such as weighing, mixing, filtration and solid-phase extraction of samples for automatic insertion into HPLC systems, transfer to UV-Vis spectrophotometers and gathering in an EasyFill Sample Collection Module. 

There are three different solid-phase extraction (SPE) methods that differ with respect to the column used, pre-extraction sample treatment, post-extraction sample treatment and internal standard. All three SPE methods extract GHB from urine and blood, derivatize with BSTEA with 1% TMCS, and detect analytes by GC-MS in the El mode with either SIM or the full-scan mode. The ions monitored for the GHB di-TMS derivative are miz 233, 234 and 235 with care being taken to avoid the ions that are common between di-TMS GHB and di-TMS urea, at m/z 147, 148 and 149. Urea is a naturally occurring compound in urine and care must be taken that its derivative does not interfere. 

In this chapter, we first discuss the implications of soil and compound properties on sample pre-treatment and extraction procedures. Different detection methods can be used depending on compound features which are more or less specific. The effort necessary for complete identification is described. Examples of analyses of different groups of compounds are described in more detail. 

The automation of liquid-liquid extraction processes is of great interest on account of the relevance of this technique to the sample treatment and of the technical complexity of such processes when carried out manually. 

The result of 2D phoresis crucially depends on sample, sample treatment, and sample resolution. How do you extract (for example) the proteins from a liver sample Dissolve it directly in sample buffer Grind first in liquid nitrogen and then mix with sample buffer Lyophilize first and then dissolve in sample buffer No agreement has been reached yet. The next question is also unclear. What is the best sample buffer Because the first step of 2D phoresis is lEF, the proteins have to keep their own charge. That means you cannot dissolve with SDS. Nevertheless, the sample buffer has to dissolve as many proteins as possible and split them into subunits. Furthermore, it must prevent aggregation. Finally, the sample buffer should denature all proteases. Which sample buffer can do that None But some come close to this ideal (however, not very close). 

Ortiz AIC, Albarran YM, and Rica CC (2002) Evaluation of different sample pre-treatment and extraction procedures for mercury speciation in fish samples. Journal of Analytical Atomic Spectrometry 17 1595-1601. 

Although the limiting factors in the use of MS as analytical tools are the high cost of equipment, complex laboratory requiranents, and limitations in the type of solvents used in extraction and separation, in recent years this technique has become very popular, because it allows a reduction in sample treatment, and it is a universal, selective, and sensitive detection mode. Furthermore, the reliability of the obtained results is usually increased. 

A FI multisensor system comprising potentiometric sensors of different types for the determination of free cyanide activity in basic solutions for extraction of noble metals has been developed [35]. Solvent polymeric membrane sensors based on metalloporphyrin and crystalline sensors were combined in the sensor system. The sensors of different types were built into the system to form a multisensor detector. The FI multisensor was also beneficial due to computerizing of measurements, automatic sampling, and sample treatment and also due to minimizing amounts of reagents. Preparation of sensor membranes is described below. 

In this chapter chromatographic folate methods for various applications are presented. Sample treatments including extraction, cleanup, and deconjugation steps are also discussed. 

This chapter focuses on LC—MS/MS applied to pesticide residue analysis, as this technique is the most attractive and efficient nowadays for developing MRMs [11], including both parent pesticides and metabolites. Sample treatment (mainly extraction and cleanup) are briefly commented on, with emphasis on those commonly applied in MRMs. A brief mention is made of problematic pesticides that do not fit in MRMs and consequently need to be determined with individual-specific LC—MS/MS methods. The use of HR MS in combination with LC also is briefly treated, either for the investigation of parent pesticides or for metabolite research, as this is a field of major interest at present. 

It is useful to compare various sampling methods to quantitative chemical analysis and to list their respective advantages and limitations (Table 6.3). In fact, an analysis is only as good as the sample which has been introduced into the analytical instrument. The ideal way to carry out a quantitative analysis with a sampling technique is to transfer an analyte completely from the sample matrix to the analytical apparatus. This means that in principle quantitative analysis of an additive is well carried out by dissolution (100% recovery), especially when the procedure restricts additional handling (evaporation, preconcentration, redissolution, etc.). The routine application of )uSEC-GC is a case in point. For quantitative analysis, most instruments require a solution. On-line combinations of sample treatment and analytical systems are being studied intensively. The idea behind such systems is to perform sample extraction, clean-up and concentration as an integral part of the analysis in a closed system [14]. 

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. 

Liquid samples might appear to be easier to prepare for LC analysis than solids, particularly if the compounds of interest are present in high concentration. In some cases this may be true and the first example given below requires virtually no sample preparation whatever. The second example, however, requires more involved treatment and when analyzing protein mixtures, the procedure can become very complex indeed involving extraction, centrifugation and fractional precipitation on reversed phases. In general, however, liquid samples become more difficult to prepare when the substances are present at very low concentrations. 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

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