Derivatization agent selection

It is important not only that a multiplicity of compounds in the sample mixture may be selectively derivatized - as was shown for Type III reactions - but also that one racemate may be derivatized with a multiplicity of derivatizing agents (Fig. 7-17). Although this approach can be used to optimize the analogues of a compound [28, 29], it is of special interest when a compound is required to be separated on a preparative scale. 

Once the plate is sprayed with a derivatizing agent, it needs to be dried in the oven as shown in Fig. 13.3. Once dried, the plate is now ready for viewing and photodocumentation. The HPTLC plate is placed in the Reprostar viewing cabinet, the proper light source is selected,... 

SPME Fiber. A 65 pm poly(dimethylsiloxane)/divinyl benzene (PDMS/DVB) fiber coating (Supelco, Bellefonte, PA) was used in this method. This fiber coating was selected for its ability to retain the derivatizing agent and for its affinity for the PFBOA-aldehyde oxime (7). 

A new, fast, sensitive, and solventless extraction technique was developed in order to analyze beer carbonyl compounds. The method was based on solid-phase microextraction with on-fiber derivatization. A derivatization agent, 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBOA), was absorbed onto a divinyl benzene/poly(dimethylsiloxane) 65- xm fiber and exposed to the headspace of a vial with a beer sample. Carbonyl compounds selectively reacted with PFBOA, and the oximes formed were desorbed into a gas chromatograph injection port and quantified by mass spectrometry. This method provided very high reproducibility and linearity When it was used for the analysis of aged beers, nine aldehydes were detected 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal. (107 words)... 

Although tetracyclines possess the inherent ability to fluoresce, few methods exploiting this property have been reported (300, 306, 309). Instead, fluorometric methods based on the reaction of tetracyclines with suitable derivatizing agents have been developed. The use, for example, of zirconyl chloride as a fluorescence label in the postcolumn derivation of tetracyclines, has allowed highly selective and sensitive detection of these antibiotics in animal tissues (294, 295). 

Chemical derivatization of an analyte is performed to improve the selectivity and sensitivity of that analyte. There are two approaches to the use of derivatizing agents in HPLC. Precolumn derivatization, which is performed before the analytes are separated, is most commonly used for small molecules such as amino acids, whereas postcolumn derivatization, which is performed after the separation but before the analytes reach the detector, is often used for larger molecules such as peptides. 

Peptides are commonly detected by absorbance at 200-220 nm. However, most of the compounds present in wine may interfere in the ultraviolet detection of peptides when low wavelengths are used. Thus, for the analysis of these compounds it is useful to apply sensitive and selective detection methods. To this end, it is possible to form derivates of the peptides that can be detected at higher and more specific wavelengths. Detection by fluorescence can also be used to detect peptides containing fluorescence amino acids (tyrosine and tryptophan). For peptides without this property, the formation of derivates with derivatizing agents have been proved to be very useful (Moreno-Arribas et al. 1998a). 

The study was performed employing GC-MS, using bis-trimethylsilyl-trifluor-oacetamide (BSTFA) as derivatization agent during sample preparation. The aim of the study was to compare the metabolic profiles of urine samples from patients with liver cancer (n = 20) and healthy volunteers (n = 20) and, subsequently, to develop a diagnostic model that would include selected metabolites of potential diagnostic significance in HCC [21]. 

Note 3. The conditions for the derivatization are selected to ensure complete derivatization. Alternatively, N,0-bis-trimethylsilyltrifluoroacetamide can be used as silylating agent. Docosane or tetracosane (in pyridine or dioxane solution) can be used as internal standard. The homogeneity of the reaction mixtures has to be considered in quantitative work. 

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