Chemical pretreatment method procedure

The measurement of Bi in body fluids and tissues may be achieved using either ETA—AAS or hydride generation techniques. Rooney [101] compared these procedures and reported that the latter was the method of choice. The severe molecular absorption interferences at 213.2 nm necessitate some form of chemical pretreatment for ETA—AAS. Thomas et al. 

Most small peptides derived from protein sources contain a variety of polar and non-polar amino acids and as such are more difficult to handle. Nevertheless appreciation of the problems and considered chemical manipulation have allowed their MS elucidation [177-184] although a practical limit of about six amino acids in the peptide is reached before degradative procedures become advisable. An important step before sequencing a peptide by mass spectrometry is whenever possible to obtain the amino acid content by hydrolysis and conventional column chromatographic analysis. This assists in the selection of any chemical pretreatment and with the spectral interpretation. A variety of small peptides has been identified by a combination of methods and include 5 - 0X0 - L - prolyl - L - histadyl - L - prolinamide (2-pyrollidone-5-carboxylyl-... 

The most spectacular developments in the field of organic chemistry of sea water are linked with the detection of specific compounds directly in sea water without any major chemical pretreatment or concentration procedures. Whether the findings, when employing these methods on a wider scale, fit in with earlier chemical oceanographic theories for the formation, distribution and decomposition of organic matter, remains to be seen. 

Ultimately, chemical engineering methods and technology are needed to transform this molecular and empirical chemistry into a real process. This chemistry must be understood in terms of many scale-up, design and simulation issues that will influence the economics of the process. For example, process equipment and operating procedures in supercritical fluids require special attention to safety issues because of the high pressures involved. There is an economic penalty in achieving the compression required to reach operating pressures and to recover products at ambient conditions. Sometimes extensive pretreatment of feeds is required or a specialized co-solvent may have to be added. 

Joni et al. presented acidic SIL catalyst materials for slurry-phase alkylation reactions, in which the IL film remained free flowing on the support surface while being flxed to the support by capillary force and physical adsorption [23]. They pretreated the support material prior to impregnation with the acidic IL in order to obtain materials with strictly reproducible catalytic performance. Chemical pretreatment was achieved by contacting a solution of [EMIMlCl/AlClj = 1/2 in dichloromethane with the calcined support, followed by a washing procedure that removed all excess acid from the support. The pretreated supports themselves had no catalytic activity in the isomerization of diisopropylbenzenes (DIPBs), but provided a suitable support material for the immobilization of acidic chloroaluminate IL. The SIL materials obtained by this method proved to be excellent heterogeneous... 

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... 

Development of methods to prepare various fractions of samples will coincide with unambiguous characterization of each fraction on the basis of a specific criterion, which can be accomplished on several levels. In Table II, for example, the fractions are identified on the basis of nature of the pretreatment applied. Increasingly, however, more specific and detailed chemical data may need to be collected during the preparation of the sample fractions to provide documentation of the nature of the organic components being separated. This process can be particularly well illustrated in the procedures applied to the dating of bone (see the following section). 

In the present chapter silica gel was activated in the following two ways. One method was to activate it in the atmosphere Silica gel (Wako Pure Chemical Industries, Ltd., Wakogel Q-23 for chromatography) was heated at 200°C for 24 hr in the atmosphere and then cooled to room temperature in a dry atmosphere. Hereafter, the silica gel thus pretreated is referred to as SG200A and the silica gel pretreated at 800°C in the same way as SG800A. The other method was to activate it in a vacuum Silica gel was heated at 200°C for 5 hr at a pressure of less than 2 x lO Torr and all the succeeding procedures for adsorption was carried out in a vacuum (SG200V). 

In cellulosic ethanol production processes, a pretreatment procedure is needed to disrupt the recalcitrant structure of the lignocellulosic materials so that the cellulose can be more efficiently hydrolyzed by cellulase enzymes [2], These pretreatments include physical, biological, and chemical ways, such as uncatalyzed steam explosion, liquid hot water, dilute acid, flow-through acid pretreatment, lime, ammonium fiber/freeze explosion, and ammonium recycle percolation [3, 4], Most of these methods involve a high temperature requirement, which is usually achieved through convection- or conduction-based heating. 

A few of the many manuals on chemical analysis which include instructions on sample collection may be mentioned. For over 100 years, AOAC INTERNATIONAL, has published detailed experimental procedures for sampling, subsampling and pretreatment of natural materials with the latest volume (Horwitz 2000) containing procedures for materials such as agricultural liming materials, fertilizers, plants, animal feed and dairy products in various chapters. A chapter on sampling dairy and related products is in the book edited by Marshall (1993) on Standard Methods for the Examination of Dairy Products. Specific sampling procedures for various food commodities are summarized by Ihnat (1982), based mostly on the AOAC manual. 

---