Other derivatization agents

Trifluoroacetyl derivatives are, in fact, reported [200] to exhibit shorter retention times at lower temperatures than the corresponding trimethylsilyl derivatives, a 

Special methods exist for the simultaneous derivatization of two hydroxyl groups, particularly when located on adjacent carbon atoms. Ketal formation — reaction of a diol with an aldehyde or ketone to form a 1,3-dioxolane derivative — is the most obvious approach for example, 20,21-dihydroxycorticosteroids have been converted to acetonides [203]. 

A somewhat more elaborate derivatization through ketal formation permits simultaneous derivatization of three functional groups of 17,21-dihydroxy-20-oxo-steroids such as cortisone with formaldehyde [204]. 

Ketalization, however, requires acidic catalysis, with its potential for damage to some substrates. Boronic acids [RB(OH)2] have accordingly been advanced [205] as diol derivatization agents capable of functioning under neutral conditions. The 

Some boronates are susceptible to hydrolysis, but on the whole, gas-chromatographic properties are good and mass-spectral molecular ions are generally easily seen. 

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Perfluoro)acyl anhydrides Common silylation reagents Other derivatizing agents Reaction tubes for GC-derivatization... 

Ogawa and Fritz (1985) developed a method for the identification of acrolein in water. A known volume of water is passed over a column of zeolite that traps the acrolein. The column is then eluted with acetonitrile, and derivatization using DNP follows. By following this procedure, a sample that can be analyzed by HPLC is obtained. Other derivatizing agents that have been used successfully for the monitoring of acrolein in the environment include dimedon, phenylhydrazone, 4-hexylresorcinol, and 3-methyl-2-benzothiazolone (Altshuller and McPherson 1963 Peltonen et al. 1984). 

In later studies, other derivatization agents were proposed to enhance the... 

Other derivatizing agents that can be used are shown in Table 4. 

Diesters. Many of the diester derivatives are commercially important. The diesters are important plasticizers, polymer intermediates, and synthetic lubricants. The diesters of azelaic and sebacic acids are useflil as monomeric plasticizing agents these perform weU at low temperatures and are less water-soluble and less volatile than are diesters of adipic acid. Azelate diesters, eg, di- -hexyl, di(2-ethylhexyl), and dibutyl, are useflil plasticizing agents for poly(vinyl chloride), synthetic mbbers, nitroceUulose, and other derivatized ceUuloses (104). The di-hexyl azelates and dibutyl sebacate are sanctioned by the U.S. Food and Dmg Administration for use in poly(vinyl chloride) films and in other plastics with direct contact to food. The di(2-ethylhexyl) and dibenzyl sebacates are also valuable plasticizers. Monomeric plasticizers have also been prepared from other diacids, notably dodecanedioic, brassyflc, and 8-eth5lhexadecanedioic (88), but these have not enjoyed the commercialization of the sebacic and azelaic diesters. 

A large number of other silylating agents have been described for the derivatization of phenols, but the first two are among the most common. ... 

At this point, the anaiyte may not be amenabie to UV, FL, or EC detection. In this case, the best course of action may be to choose LC/MS (see Section 4.2). However, one other option is to use a pre- " or post-coiumn derivatization step to increase the detectabiiity of the anaiyte with respect to FL or UV. Fluorescent or UV labels are available for carboxylic acids," amines, phenols, and thiols. The decision to use pre- or post-column derivatization is predicated upon the functionality of the analyte available for derivatization and the rate and extent of the reaction between each derivatizing agent and the analyte. 

Beer was also analyzed by gas chromatography/mass spectrometry (GC/MS) without being derivatized by PFBOA to make sure that there were no other sources of m/z 181 besides the derivatization agent. (Adapted from Vesely... 

Depending on the derivatizing agent used, spectrophotometric or fluorometric detectors are usually employed. Electrochemical detection of underivatized amino acids is limited to amino acids possessing aromatic or sulfur-containing side-chain, even if derivatization procedmes to attach electrochemical active moieties to the amino acids can be employed, as well as other approaches... 

Trimethylsilyl derivatives are prepared by treatment with BSA alone [310,311] or with the addition of TMCS [312,314] in a suitable solvent (acetonitrile, pyridine, tetra-hydrofuran) or even without a solvent. For completion of the reaction, 10—20 min at 50°C are necessary [312], but as little as 30 min at 150°C has been reported for a stoppered vial with the use of a solvent [311], BSA alone can be used to advantage if pico-mole amounts are to be derivatized. The reaction products are said to decompose in dilute solutions even though pure BSA is used for dilution. At concentrations around 1 ng//d, up to 40% decomposition of the products is observed if diluted with BSA— acetonitrile (1 4), 100% decomposition occurs in 20 min. Of other silylating agents, e.g., HMDS and TMCS have been tested, but conversion into derivatives was not complete [311]. Silicone stationary phases of the SE-30, OV-1 and similar types have been used in the analysis. In most instances, temperature programming is required. Using the FID (in almost all instances), the detection limit is about 20 ng for T4 and 5—20 ng for T3, whereas with the aid of an ECD amounts about two orders of magnitude smaller can be detected [310,314]. Fig. 5.21 demonstrates a typical separation of five iodoamino acids and Tyr on 0.5% of SE-30. 

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