Methods Requiring Sample Pretreatment

The most common method for preparing samples for pretreatment and subsequent measurement of IR spectra is the self-supporting pellet technique. In this 

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Unfortunately, extraction procedures are often elaborate and labour intensive since many of the polymer matrices are poorly soluble or insoluble. For this reason, substantial efforts have been directed towards additive analysis without prior separation from the polymer. Chapter 9 deals with direct methods in which such separation of polymer and additive can be omitted. Yet, this direct protocol still requires sample pretreatment (dissolution) of the polymer/additive system as before. 

Destructive methods the determination of the amount of a substance in a material usually leads to the destruction of the test sample. This is realised by pretreatment techniques such as acid digestion, fusion, extractions etc. to bring the test sample into a liquid or other simple form compatible with the final determination technique or instrument. Nearly all modern methods of measurements, e.g. spectrometry, require sample pretreatment procedures. 

GF-AAS methods combine a very high atomization efficiency with a 100-1000 fold increase in sensitivity compared to the conventional flame technique. For this reason and also because of the capability of handling solid samples as well as samples which normally requires sample pretreatment, GF-AAS is one of the most popular methods in trace and ultratrace element determinations in clinical chemistry. 

On the other hand, the development of a MEEKC allowed the determination of the same food colorants with most instances not requiring sample pretreatment. Tlie effects of SDS surfactant, organic modifier (acetonitrile), cosurfactant, and oil were examined to optimize the separation. A highly efficient MEEKC separation method, where the eight colorants were separated with baseline... 

With these types of methods, the sample is concentrated by causing the sample plug to move across a boundary between two buffers with different compositions in a capillary or microchannel. The two buffer compositions are chosen such that the analytes of interest will move more slowly through one buffer than the other. As the sample plug moves from the fast side of the boundary to the slow side, it is compressed and thus concentrated. Concentration enhancements of the order of 100-1,000-fold are typical [6]. However, these methods are not universally applicable and often require sample pretreatment or extraction to produce a sufficiently clean sample for stacking. 

The determination of chromium can be performed by a great number of physicochemical methods, with different detection powers, working range, and application field. Here, only those techniques that have found more general applications in different fields can be briefly discussed. The selection of a method for a special analytical task is not only dependent on the detection power and other performance characteristics of the technique, but is highly dependent on the sample constitution, the required sample pretreatment and means of sample introduction, and, last but not least, on its availability (Table 3). 

Spectroscopic, luminescence, turbidimetric, and electrochemical methods of detection have been combined with SIA for the successful determination of amino acids, sugars, and trace elements in matrices such as meats, vegetables, breads, wines, juices, and milks. Many of these methodologies required sample pretreatment and whilst most performed this in an offline manner there have been some reports of online sample cleanup. Microwave assisted digestion was performed in-line for the determination of phosphorous, calcium, magnesium, and iron in slurried foodstuffs, wine, milk, and soft drinks whilst gaseous diffusion allowed interference removal for the determination of urea in milk. 

Conventional speciation techniques require sample pretreatments such as digestion that may alter the chemical species of the element of interest. As shown above, quantitative speciation by XANES offers an excellent method for elucidating the chemical species of an element in biological tissues and in intact organisms with minimal sample preparation. The detection limits are generally in tens to hundreds of tgg level, but they are dependent on both the incident X-ray intensities and specific atoms. For example, the detection limit for selenium speciation may reach 0.2 pgg"... 

LC-GC is a very powerful analytical technique because of its selectivity and sensitivity in analysing complex mixtures and therefore it has been used extensively to determine trace components in environmental samples (2, 5,77). LC allows preseparation and concentration of the components into compound types, with GC being used to analyse the fractions. The advantages of on-line LC-GC over the off-line System are, first, the less sample which is required and, secondly, that there is less need for laborious sample pretreatment because the method is automated (78). 

Also, subcritical (hot/liquid) water can be used as a mobile phase for packed-column RPLC with solute detection by means of FID [942]. In the multidimensional on-line PHWE-LC-GC-FTD/MS scheme, the solid sample is extracted with hot pressurised water (without the need for sample pretreatment), and the analytes are trapped in a solid-phase trap [943]. The trap is eluted with a nitrogen flow, and the analytes are carried on to a LC column for cleanup, and separated on a GC column using the on-column interface. The closed PHWE-LC-GC system is suitable for many kinds of sample matrices and analytes. The main benefit of the system is that the concentration step is highly efficient, so that the sensitivity is about 800 times better than that obtained with traditional methods [944]. Because small sample amounts are required (10 mg), special attention has to be paid to the homogeneity of the sample. The system is... 

In contrast to direct mass spectrometry used in the El mode, ESI often requires specific pretreatments of the samples to purify the components of interest, to increase their yield of ionisation and consequently to improve selectivity and sensitivity. It is thus not a preliminary step of analysis but a method that forms part of an analytical strategy that allows the presence of well preserved high molecular long chain compounds to be shown before their fine characterisation by ESI techniques (Regert et al., 2003a Mirabaud, 2007 Mirabaud et al., 2007). 

The analysis of organic materials by GC/MS requires a pretreatment of the sample, one important step being the extraction of the compounds of interest from the matrix. This is crucial with resinous materials from historical objects due to the uniqueness of such samples and to the small amount of the organic fraction usually contained in them. This means the extraction methods must be highly efficient. The methods generally adopted can be divided into three main groups ... 

The greatest area of applications of this type of ECL has been in the analysis of pharmaceutical compounds with amine functionality. The reader is directed toward the previously mentioned review articles and Table 1 for further details [12, 14-16], Many methods have also been successfully applied to real samples in the form of body fluids or pharmaceutical preparations, although sample pretreatment such as deproteinization, centrifugation, and neutralization followed by a chromatographic step to remove interfering species is often required. Limits of detection are typically in the range 10-9—10 12 M. Figure 4 shows examples of some classes of pharmaceutical compounds that have been determined by Ru(bpy)32+ ECL. 

Automatic analysis consists essentially of the same steps as the corresponding manual method (p. 4). In some cases this may be simple, the requirements amounting to a mechanical device for presenting the sample to the detector, a timer to control the time of measurement and a data recorder. However, if sample pretreatment and separations are necessary a variety of wet chemical stages needs to be automated. Such automated steps may be included in what remains essentially as an operator procedure. For... 

Potentiometric measurements with ISEs can be approached by direct potentiometry, standard addition and titrations. The determination of an ionic species by direct potentiometry is rapid and simple since it only requires pretreatment and electrode calibration. Here, the ion-selective and reference electrodes are placed in the sample solution and the change in the cell potential is plotted against the activity of the target ion. This method requires that the matrix of the calibration solutions and sample solutions be well matched so that the only changing parameter allowed is the activity of the target ion. 

The determirration of caffeine has always been problematic with specific methods or modifications being required for specific foodstrrffs. The proposed derivative spectrophotometry and PLS-1 involve sample pretreatment with basic lead acetate. 

Altria, K. D., and Rogan, M. M. (1990). Reductions in sample pretreatment requirements by using high-performance capillary electrokinetic separation methods. J. Pharm. Biomed. Anal. 8, 1005-1008. 

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