Detection of Small Organic Molecules

There is a limited number of studies on aptasensors (aptamer sensors), particularly for the detection of small organic molecules. An electrochemical aptasensor was developed by Kim et al. " for the detection of tetracycline using an ssDNA aptamer that selectively binds to tetracycline as the recognition element. The aptamer was highly selective for tetracycline and distinguishes minor structural... 

Kibbey CE. Quantitation of combinatorial libraries of small organic molecules by normal-phase HPLC with evaporative light-scattering detection. Molecular Diversity 1, 247-258, 1996. 

Taylor EW, Qian MG, Dollinger GD. Simultaneous online characterization of small organic molecules derived from combinatorial libraries for identity, quantity, and purity by reversed-phase HPLC with chemiluminescent nitrogen, UV, and mass spectrometric detection. Anal Chem 1998 70 3339-3347. 

Because of the variety of interfaces and the low detection limits, hyphenated mass spectrometers are among of the fastest growing markets for scientific instrument manufacturers in the 1990s and beyond. Every available type of chromatographic separation has been analyzed by mass spectrometry from desorption methods for TLC plates26 to online CE-MS.27,28 Not all techniques are routinely used for the characterization of small organic molecules of pharmaceutical interest (Table 4). The two workhorse instruments for the characterization of small molecules are GC-MS and... 

Kibbey, C.E. Quantitation of Combinatorial Libraries of Small Organic Molecules by Normal-phase HPLC with Evaporative Light-scattering Detection, Mol. Divers. 1,247-258 (1996). 

Taylor, E.W. Qian, M.G. Dollinger, G.D. Simultaneous Online Characterization of Small Organic Molecules Derived from Combinatorial Libraries for Identity, Quantity, and Purity by Reversed-Phase HPLC with Chemiluminescent Nitrogen, UV, and Mass Spectrometric Detection, Anal. Chem. 70,3339-3347 (1998). 

Model predictions can also be inaccurate due to the incompleteness of the chemical model, e.g. if some reactions or species were incorrectly omitted from the mechanism. If the missing species or reactions are completely missing from the database used by the model-construction software, there is no easy way to detect them (though perhaps a human expert might notice the omission in the tree databases described in Section II). There is certainly chemistry which is not well understood, even in the well-studied thermal gas-phase chemistry of small organic molecules for example some of the important reactions of peroxyl radicals are still unclear (Taatjes, 2006), the true reaction path for CH + N2 was only recently identified (Moskaleva and Lin, 2000), and recently some reactions that occur over ridges rather than saddle points have been identified (Townsend et al., 2004). It will be some time before there is a community consensus on how to correctly generalize from some of these observations. 

The direct interaction of small organic molecules with receptors immobilized on the sensor surface is difficult to detect. Two approaches may be used to detect or quantify the presence of small analytes in a process stream, displacement assays or competition assays. 

Matrix-assisted laser desertion ionization (MALDI) was first described by Karas and Hillenkamp in 1988 [469]. At that time it was a revolutionary method for the ionisation and analysis of large biomolecules. Now many more MS methods have been devised, but the analysis of complete protein masses is still only possible by MALDI [470]. With MALDI, a matrix (crystals of small organic molecules) with a small amount of analyte is ionised by a short laser pulse at a wavelength close to the adsorption band of the matrix molecules. This produces predominantly singly charged molecular ions, which are detected by the TOE spectrometer. The ana-... 

The separation and detection of small organic and inorganic ions is an important activity in the pharmaceutical industry. CE is routinely used for ion analysis in the pharmaceutical industry for a number of applications, these include counterion determination, stoichiometry, salts, and excipients in drug formulations. Most pharmaceutical molecules are charged and are commonly manufactured... 

EMIRS has been successfully applied to many systems. Briefly it can be mentioned the study of adsorbates at the electrode surface [10], the detection of adsorbed reaction intermediates for the oxidation of small organic molecules [12], and the determination of the water structure in the double layer [13]. However, the potential modulation in EMIRS is its drawback, since it prevents the study of irreversible processes as the system must return to the same conditions each time the potential is changed. Other important limitations of EMIRS are related to both the electrical and chemical relaxation effects caused by the potential modulation at 12 Hz. The electrical relaxation is due to the high ohmic drop of the electrolyte confined in the thin solution layer required for the in situ measurements. The chemical relaxation is due to ion migration induced by the change in solution composition caused by the electrode potential change. These aspects have been discussed in detail in the following text [14-16] (see Sect. 3.4.2.3). 

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