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Derivatisation reagents

Substances that cannot be directly measured in UV/VIS or F mode can generally be quantitated after chemical derivatisation [404]. Transfer of derivatising reagents onto the plate can be accomplished by spraying or by immersing the plate using an automatic immersion device. Such a device controls the immersion rate,... [Pg.223]

The high water-solubility of surfactants and their, often more polar, metabolites prevents direct application of gas chromatographic separation (GC) with appropriate detection. The necessary volatilisation without thermal decomposition can be achieved by derivatisation of the analytes, but these manipulations are time- and manpower-consuming and can be susceptible to discrimination. Additionally, each derivatisation step in environmental analysis is normally target-directed to produce volatile derivatives of the compounds to be determined. Unknown surfactants that are simultaneously present, but differ in structure and therefore cannot react with the derivatisation reagent, are discriminated under these conditions. [Pg.64]

Analyses of derivatives of NPEOs have been carried out with a large number of derivatisation reagents. Among them, polyfluorinated reagents, such as pentafluorobenzoyl chloride and heptafluorobutyric... [Pg.91]

Silylating reagents are another popular class of derivatisation reagents. These reagents introduce residues into the sample, although this is not a great problem if the analyte is relatively involatile. An example of a silylation reaction is shown on page 226. [Pg.220]

Fig. 2.2.2 a Reaction of tri-n-butylphosphine as a reducing agent, b Reaction of the derivatisa-tion of Hey with ammonium 7-fluorobenzo-2-oxa-l,3-diazole-4-sulfonate (SBDF), which is a fluorescent derivatising reagent... [Pg.95]

Often it is required to detect compounds with no or only very weak chromophores such as sugars and amino acids. Refractive index detectors and mass sensitive detectors can be used but they are relatively insensitive in the context of biological sample concentrations. Indirect detection using a UV or fluorescent eluent can also be employed. However, the most common approach is the use of derivatisation. Derivatisation of some chemically reactive moiety on the analyte can be performed in two modes. In post-column derivatisation the sample is separated first and then reacted with a flowing stream of derivatising reagent being pumped into... [Pg.213]

The types of derivatising reagents that may be used are shown in Figure 12.5. The products formed are called diastereomers. These compounds which possess two chiral centres have different physicochemical properties and are therefore separable by LC on conventional achiral LC columns. [Pg.256]

Sample treatment Addition of liquids, solvents, derivatising reagents, etc. Addition of solids... [Pg.547]

Dialkylacetals of DMF react instantaneously and quantitatively with acids, amines, amides, barbiturates either in solution or directly by on-column derivatisation using a mixture of the analyte and reagent. Methyl and butyl derivatives can be prepared. There is a considerable range of derivatisation reagents available and the reader is referred to the literature and the reference texts quoted [47-49]. In addition, many suppliers of... [Pg.220]

In the HPLC of drugs and poisons, derivatisation reactions, although sometimes used to stabilise an analyte, are seldom needed to achieve satisfactory chromatography except when performed to permit the separation of enantiomers for example Srinivas and Igwemezie list a number of derivatisation reagents that have been used to facilitate enantiomer separations by HPLC-ECD. However, derivative formation is chiefly used to enhance the selectivity and sensitivity of detection. Ruorescent derivatives are the most popular, but derivatisation has also been used to enhance UV or EC detection characteristics. " ... [Pg.69]

If oxidation of thiols is a problem they can be protected by reaction with thiol-derivatising reagents, such as NEM. When complex sample preparation procedures are needed, an internal standard should be used. For thiols being measured by HPLC-ED, the only suitable compounds are other thiols. The internal standard is thus likely to be unstable, with an in vitro half-life not necessarily the same as that of the analyte and mixed disulfides may form. Nevertheless, Drummer et al used A/-acetylcysteine as the internal standard in an assay for D-penicillamine. [Pg.84]

In HPLC most derivatising reagents are used to increase sensitivity by forming chromophores and fluorophores. There would seem little point in forming electro-phores of already electroactive compounds, such as thiols. However, Shimada et al. used A -(4-anilinophenyl)maleimide to confer not only electroactivity, but also stability to iV-acetylcysteine, cysteine, GSH and D-penicillamine. The reaction was complete in 10 min at 0 °C and the derivatives were separated in 12 min using isocratic RPLC. They also used derivatisation with a related compound, yV-(4-dimethylaminophenyl)-maleimide, to measure captopril in plasma. ... [Pg.90]

Both sample and matrix effects influence quantitative TLC using scanning densitometry. The sorbent matrix influences the shape of calibration curves impurity gradients, resulting from contamination of the layer, or application of derivatising reagents are common sources of baseline instability. Chemical reactions catalysed by the sorbent layer are also a source of sample instability. Fluorescence quenching and fluorescence enhancement effects can influence the reliability of quantification in the fluorescence mode [97]. Densitometry has been reviewed [100]. [Pg.632]


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Derivatisation

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