Derivatisation agents

Modifier addition Static soaking, adding derivatising agents or adding secondary modifiers... 

NMR can be a powerful tool for determination of enantiomeric excess or absolute configuration of the optically active compounds, however, these processes require the use of some auxiliaries, for example, chiral lanthanide shift reagents or chiral derivatising agent. In many cases, the starting point for determination of enantiopurity of amines, amino acids or diols is the formation of chiral imines. 

In determination of the enantiomeric purity of aliphatic primary amines, the use of (S-aminoalcohols and ot-amino acids 1R(—)-myrtenal as a derivatising agent has been tested.1... 

Derivatising agent Determined amino acids Reference... 

A deactivated silica pre-column is also a fundamental tool when pyrolysis is performed, since it partially helps in avoiding the contamination of the analytical column with underivatised polar compounds. Blanks (that is the pyrolysis of the derivatising agent without sample) must be run between analyses to ensure the absence in the chromatograms of any signals that do not belong to the sample. 

The diversity of markers that are reported in the literature for the three proteinaceous binders, even when the same derivatising agent is used, highlights how several aspects come together to determine the final pyrolysis products. Animal glue for example, when pyrolysed at 600°C in the presence of HMDS, gives rise to different markers depending on the pyrolyser and instrumental set-up used ... 

The pyrolysis of glycerolipid materials requires the use of a suitable derivatising agent, in order to increase the detectability of fatty acids and dicarboxylic acids, which may be present in a mature paint film as free acids, metal soaps, as well as esterified with glycerol. The oils and fats commonly used in samples from works of art have been analysed by means of pyrolysis using TMAH [12,23,25,26,32 38], and HMDS [37,39]. 

To demonstrate these aspects, the different pyrograms obtained from the pyrolysis of aged linseed oil samples using different derivatising agents and different pyrolysers are shown. 

C the sample was inserted in a prepyrolysed quartz tube and admixed with 5 /d of derivatising agent, i.e. HMDS or TMAH 25% aqueous solution. 

Plant resins are discussed in detail in Chapter 12. Since plant resins were once common additives for paint binders, this section briefly reviews the literature, focusing on the use of different derivatising agents. 

Fresh plant resins have been characterised by means of pyrolysis coupled to GC/MS without the use of a derivatising agent. However, many markers used for the identification of resins in samples from works of art are often not cogent, and moreover they disappear during ageing [42]. 

AEOs have been analysed by HPLC and UV or fluorescence detection after suitable derivatisation. The derivatising agents proposed so far are phenyl isocyanate [80,81], 1-anthroylnitrile [82], 3,5-dinitro-benzoyl chloride [83], naphthyl isocyanate [84] and naphthoyl chloride [84], However, the lack of fluorescence activity and the need for synthesis through a multistep reaction for some derivatising agents limits their application in a real-world analysis. In fact, only a few of them were applied in the determination of AEOs in environmental samples. Zanette et al. [84] developed derivatisation and separation... 

Chiral platinum (and palladium) ethene complexes derived from Diop [2,2-dimethyl-4,5-bis-(diphenylphosphinomethyl)-l,3-dioxolane] act as chiral derivatising agents for the 31P-based NMR assay of the enantiomeric purity of certain chiral alkenes and allenes80. 

Wu WS, Stoyanoff RE, Szklar RS, et al. 1990. Application of Tryptamine as a derivatising agent for airborne Isocyanate determination. Part 3 evaluation of total isocyanates analysis by high-performanee liquid chromatography with fluorescence and amperometric deteetion. Analyst 115 801-807. 

Simple colorimeters, used for routine analysis, are visual comparators related to Nessler tubes. The latter are made of flat-bottomed glass tubes with a volumetric mask and filled with reference solutions of varying concentrations (and possibly derivatising agents). The solution to be analysed, placed in an identical tube, is inserted beside the series of standard solutions. 

R and S diastereomers (AA5 = 10 ppm) and experience a large lanthanide induced shift with the CH3 resonating at +21 and +31 ppm respectively for (It)- and (5)-lactate respectively (c.f. +1.3 ppm in the free form). The large shifts exhibited by this unique chiral derivatising agent may be compared to the much smaller AA8 values reported for shift reagents which are generally of the order 1 ppm, and often <0.1 ppm. 

Suggest a derivatising agent for the HPLC analysis of the optical purity of the 10-camphorsulphonic acid salt obtained in step h. 

For a number of reasons it is usually preferable to use a chiral stationary phase (CSP) rather than a chiral derivatising agent. A CSP will normally be preferred to a chiral mobile phase additive, partly because the use of a chiral selector as a mobile phase additive will lead to much... 

The simplest colorimeters, used for routine measurements, were visual comparators (Figure 9.31). Nessler tubes, used for many years, consisted of graduated flat-bottomed tubes of glass filled with different concentrations of standard solutions mixed with a derivatising agent. The solution to be analysed was placed with the same agent in an identical tube and colour was compared with that of the standards ( same colour, same concentration ). 

The method chosen was that of Johnson and coworkers (ref. 66) which involves the use of a chiral oxazaphospholidine-2-thione as a chiral derivatising agent for Ip NMR analysis of... 

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