Selective detection reagents

Primary alcohols can be selectively detected using reagent sequences involving an initial oxidation to yield aldehydes that are then reacted in acid medium with electron-rich aromatics or heteroaromatics, according to the above scheme, to yield intensely colored triphenylmethane dyes. 

In the literature, a large number of more-or-less selective detection reagents are published [1,3,17-20]. The presented selection of reagents cover reactions that can be easily performed. The reagents remain stable for days when stored in a refrigerator. 

Kudzin ZH, Kotynski A, Kielbasinski P. 1991. Application of the iodine-azide reagent for selective detection of thiophosphoryl compounds in thin-layer chromatography. J Chromatogr 588 307-313. 

Higher specificity and selectivity can be obtained by reacting -lactams with suitable reagents to form derivatives with improved ultraviolet chromophores. Thus, precolumn derivatization of penicillins with triazole-mercuric chloride and ultraviolet detection at 325 nm (71, 90, 112, 114, 115, 121, 122), 340 nm (123), or 345 nm (116) has become the method of choice for more selective detection and matrix interferences reduction. An alternative precolumn reaction using iodoacetamide as derivatizing reagent has been described in ceftiofur analysis (124), while imidazole-mercuric chloride has also been suggested for on-line postcolumn derivatization of penicillin G (69). 

The sensitivity and simplicity of an analytical method always improves when selective detection can be used. Because of detection selectivity, a sample in a complex matrix can be analysed with minimum sample preparation. Wouldn t it be ideal to have an ultra-specific reagent that would allow the determination of a compound in an environment containing thousands of substances ... 

There are few sensitive assays for the selective detection of resin-bound alcohols. Electrophilic derivatization with a chromophore-containing reagent (see, e.g., [62]) will usually give a positive result with resin-bound amines or thiols as well, and is therefore of limited diagnostic value. 

We have also employed other derivatization techniques to selectively label other moieties such as carbonyls and applied these to the selective detection of steroids [119]. Girard s Reagent P reacts with the carbonyl-containing compounds according to Equation 5. 

Steroid hormones chemical derivatization, reagent selection and optimization Derivatization of steroids to enhance LC/MS detection, e.g., LSI1 /MS, A PCI VMS, and APPP VMS. [16, 17]... 

The resulting alkyl or aryl diethyl phosphates were selectively detected at the 10-25 ng level with the P-mode FPD. Similarly, Jacob et al (36) used dimethyl thiophosphinic chloride in the presence of excess triethylamine to convert primary aliphatic, aromatic and heterocyclic amines to the corresponding N-dimethyl-thiophosphinic amides. The excess reagent was easily removed by treating the reaction mixture with methanol-sodium hydrogen car-... 

The remainder of the chapter is devoted to the discussion of two color derivatizing reagents, one irreversible the other reversible, to explore the thesis that greater selectivity is always achieved with CD detection. Results turned out to be rather surprising because for one of the reagents, absorbance detection has defied its reputation as a non-selective detector and performs better than CD. 

The development of a biosensor capable of selectively detecting a point mutation in human DNA would enable an early diagnosis of inherited human diseases. With this aim, a prototype of a sequence-selective DNA biosensor based on hybridization indicators was evaluated [90]. For the covalent immobilization of single-stranded DNA onto the carboxylic groups present on the surfaces of oxidized glassy carbon, water-soluble carbodiimide and /V-hydroxysuccinimide coupling reagents were used. 

In addition to TMS ethers, dimethylsilyl ethers [36] were studied for the analysis of alcohols and phenols. They were prepared by reaction with reagents analogous to those used for TMS ethers [dimethylmonochlorosilane and tetramethyldisilazane in pyridine (1 3 9)] and they provide shorter retention times in comparison with TMS ethers on Apiezon L. Grant [37] converted phenols into bromomethyldimethylsilyl ethers. In addition to a higher sensitivity, selective detection, permitting, e.g., phenolic substances to be determined in tars without any preliminary separation, was even achieved by using an ECD. 

Eluents must have sufficient transparency at the selected detection wavelength and Fig. 1 shows the absorption spectra of several solvents commonly employed. The spectra were recorded in 1-cm cells with water as the reference. These represent purified solvents reagent grade solvents contain impurities which can limit their use to even longer wavelengths. Buffer salts can also limit transparency. 

Compound identification is initially made by comparing sample and standard zones based on R values and colors produced by selective detection reagents. Identification is confirmed by off- or on-line combination of TLC and spectrometric methods such as visible/UV, fluorescence, FT-Raman, solid... 

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