A fast gradient reversed-phase liquid chromatography (LC) method, using an acetonitrile gradient was developed to determine the chromatographic hydrophobicity index (CHI), as reported by Valco et al. (Anal. Chem. 1997, 69, 2022-2029). The analytical method provides retention times, based on UV detection at two different wavelengths, which then are converted into CHI values after calibration with a set of test compounds. The CHI of each compound is measured at three different pH values, 2.0, 7.4, and 10.5; so using an 8-min gradient at each pH value one compound can be analyzed in approximately 24 min. The aim of this work is to improve the throughput of the CHI screening using a LC/MS approach, so the application of the LC/MS technique is an extension of the LC/UV approach previously reported by Valco et al. This approach allows contemporary injection of N compounds into the LC/MS system, the retention time of each compound can be then extracted from the selected ion recording chromatograms. The throughput of the existing screening method could be increased by N times, where N is the number of compounds injected, so only three runs are needed to determine the CHI at three different pH values for a set of N compounds. The highest value of N depends on the total number of channels that can be monitored simultaneously; in the present work, 32 channels were used. This LC/MS method has been tested for a number of commercial products analyzed as mixtures, and data obtained were compared with those coming from the classical LC/UV approach. In the same way, the method was tested for a number of compounds associated with two GlaxoWellcome projects in the antibacterial area. Data reported show that the LC/MS method can be successfully applied for analyzing compounds in mixtures and for compounds with poor UW absorption, which cannot be analyzed with the standard LC/UV method.

This paper describes the successful transfer of benzotriazole-based chemistry on solid support. The strategy followed to anchor this peculiar heterocycle on solid phase and the full analytical characterization of the various supported benzotriazoles are herein described. The chemistry assessment process on solid phase, the preparation of discrete libraries by parallel synthesis, the semiautomated purification procedures, and the complete analytical characterization of the library components are also presented and discussed.

The presence of dansyl or dabsyl chromogenic moieties in a solid-phase analytical construct, an assembly of linkers/spacers/sensitizers for improving analytical characterization, allows the accurate estimation of products from solid-phase synthesis by UV detection during liquid chromatography-mass spectrometry analysis in the cleavage solution. The spectroscopic properties of dansylated molecules have been evaluated to verify the "compound-independent UV absorption" necessary for using the chromophore in the accurate estimation. First, measurements on commercial dansylated compounds were made, then a series of construct-like molecules were prepared by solution-phase synthetic procedures and their UV properties were determined. Compound calibration curves were determined, and UV absorption was shown to be both proportional to the compound concentration and compound-independent. An example of a dansyl construct derivative was then prepared on a polymeric matrix, and an accurate estimation using the calibration curves was carried out in the cleavage solution. Good agreement was found between the calculated amount of released compound using the UV calibration curves and the calculated amount using both (1)H NMR and LC/chemiluminescent nitrogen detection quantitative techniques. Preliminary studies using the dabsyl moiety as an improved chromophore with higher wavelength and extinction coefficient are also reported.

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The composition of a commercial dehydroascorbic acid (DA) solution at pH 2 was investigated by liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) to establish the nature of its different forms and its decomposition products. In freshly prepared solutions, dimeric forms of DA and the hydrated bicyclic hemiketal of DA are the species mainly present in solution. In the presence of light, the initial dimeric species disappears over time to give other dehydrated dimers some of which decompose to the monomer. The comparison of these data with similar data obtained for ascorbic acid (AA) solutions under the same experimental conditions revealed that, in the presence of light, the aging of such AA solutions gives rise to only the hemiketal form of DA, and that no dimeric species of DA were formed. The presence of the hemiketal form of DA was not revealed by analysis of the same AA solutions using the conventional LC/UV technique. The natural form of DA from the oxidation of AA is the hydrated bicyclic form.