Sample preparation and pretreatment

In trace and ultratrace analysis with respect to minimal systematic errors, the following must be considered  

In addition, the residue of the digestion should be quantitatively dissolved in a small volume of high purity acid. The decomposition and accuracy of analytical data should be checked with the aid of certified reference materials. Possible contamination and losses of trace elements by absorption or volatilization should be avoided. 

Sample preparation, which is generally minimized for solid samples, can be a time consuming and labour intensive process, especially if trace matrix separation is required. Due to the huge variety of different matrices, of more or less complex matrix composition, many different decomposition principles have been developed. 

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SOLVENT EXTRACTION IN SAMPLE PREPARATION AND PRETREATMENT STEPS... 

The above considerations are applicable to the titanium dioxide samples prepared and pretreated following the standard procedures. The presence of significant amounts of impurities or, for example, the high-temperature pretreatment of the Ti02 samples lead usually to a more or less important decrease of the extent of hydroxylation. 

The devices based on microfluidic chip-capillary electrophoresis (microchip-CE) make use of the microfluidic chip technology for sample preparation and pretreatment prior to highly efficient separation by capillary electrophoresis using commercially available instrumentation. A list of the research and development work performed using the hyphenated microfluidic chip-CE technique is given in Table 2, showing three major areas of application. 

Currently, detection power is primarily hmited by reagent contamination. Progress in the widespread implementation of FI techniques, which feature online sample preparation and pretreatment capabilities as well as capabilities for rapid automation, should facilitate a further revolution in the use of vapor generation techniques in atomic spectroscopy. 

State-of-the-art TOF-SIMS instruments feature surface sensitivities well below one ppm of a mono layer, mass resolutions well above 10,000, mass accuracies in the ppm range, and lateral and depth resolutions below 100 nm and 1 nm, respectively. They can be applied to a wide variety of materials, all kinds of sample geometries, and to both conductors and insulators without requiring any sample preparation or pretreatment. TOF-SIMS combines high lateral and depth resolution with the extreme sensitivity and variety of information supplied by mass spectrometry (all elements, isotopes, molecules). This combination makes TOF-SIMS a unique technique for surface and thin film analysis, supplying information which is inaccessible by any other surface analytical technique, for example EDX, AES, or XPS. 

Initially, since the ionization efficiency was remarkably low in tissue section samples, miscellaneous biological molecules such as salt were included in the analysis, which posed a problem. To resolve it, it was necessary to increase the detector sensitivity of the MS device, and improvements in the preparation and pretreatment of tissue samples were very important. Our actions toward solving these problems in the past several years are described below. 

Due to its simplicity and wide applicability, PPT is important for sample pretreatment in early drug discovery when generic extraction of mixtures of candidates is more important than sensitivity. As a generic technique, PPT is attractive for high-throughput bioanalysis because it offers fast sample preparation and easy automation and requires minimal manual labor. 

TRXF was used to determine the trace elements in samples of lecithin, insulin, procaine, and tryptophan in an attempt to develop elemental fingerprints that could be used to determine the origin of the sample [80]. It was reported that through the use of matrix-independent sample preparation and an internal standard, one could use TXRF to facilitate characterization of the samples without the need for extensive pretreatment. In another work, a study was made of the capability of TXRF for the determination of trace elements in pharmaceutical substances with and without preconcentration [81]. 

Mermet, J.M. Focused-microwave-assisted reactions atmospheric-pressure acid digestion, on-line pretreatment and acid digestion, volatile species production, and extraction. In Kingston, H.M., Haswell, S.J. (eds.) Microwave-Enhanced Chemistry. Fundamentals, Sample Preparation, and Applications. ACS, Washington, DC (1997)... 

Given the great number of Isotherms published In the literature, within the scope of the present chapter we restrict ourselves to a few arbitrary examples, merely meant to illustrate certain points. As shapes of isotherms depend sensitively on the preparation and pretreatment of the sample, especially on the outgasslng conditions, these Illustrations are not necessarily representative. 

Until recently, samples for FIA were already extracted. Altered, centrifuged or pretreated in some way prior to assay. However, some sample preparation and preconcentration steps can now be accommodated in FIA. Some examples are on-line liquid-liquid extraction, solid phase extraction and ion-exchange procedures. In this way, FIA is managing to convert some traditionally labour-intensive steps into automated operations that have higher precision and faster throughput. FIA can also tolerate other sample types, such as fermentation broth samples and even gases through the use of silicon membrane separators and gas diffusion systems, respectively. 

Most of the methods for the determination of selenium in human materials require some sample preparation or pretreatment. The biotransformation of selenium in man, which is characterized by a step-wise biochemical reduction, leading to the binding to or direct incorporation of the element into proteins, apparently involves the formation of intermediate volatile species. Dimethyl selenide as well as many other organic forms of selenium and its halides are relatively volatile. 

Should the sample be filtered/treated to remove large particles, cells, or other potential interferants Many samples may require carefully optimized strategies for pretreatment prior to analysis. This is not just a requirement for sensor-based analysis and much food/environmental samples have well-established protocols for cleanup. Such elements can affect the analysis as they may block microfluidic devices or cause nonspecific binding to a number of commercially available systems. These factors are critical in sample preparation and should be investigated, where relevant. However, where possible for ease of analysis/reduction of costs pretreatments need to be kept to a minimum. 

Desorption electrospray ionization (DESI), an ambient MS technique, was used for trace detection of the explosive RDX, directly from a wide variety of surfaces (metal, plastic, paper, polymer) without sample preparation or pretreatment. Increased selectivity was obtained both by MS/MS and by performing additional experiments in which additives were included in the spray solvent. Pure water could be used as the spray solution for DESI, and it showed ionization efficiencies for RDX in the negative ion mode similar to those given by methanol/water <2005ANC6755>. 

Catalyst synthesis and pretreatment As the history of a catalyst sample is of prime importance for its subsequent activity in catalytic reactions, this subsection is devoted to a brief description of common methods of catalyst preparation and pretreatment. The preparation and pretreatment procedure determines the surface area accessible in the catalytic reaction, the distribution of active surface sites and also the chemical nature of the surface actually involved in the catalytic process. It has to be noted, however, that the detailed microscopic characterization of rare earth derived... 

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