Analyte derivatization

Despite the successful application of MALDl and DIOS in the analysis of LMM compounds, the analysis remains a challenge. This stems primarily from low ionization efficiencies due to a lack of functional groups with high proton affinity, matrix suppression effects, isobaric overlay of the matrix with the analyte, and the high volatility of many analytes. One approach to improve the analysis of LMM compounds is by derivatization. The derivatization of samples prior to MS analysis has been widely employed in gas chromatography-mass spectrometry (GC-MS) 

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Knapp, D.R., Handbook of Analytical Derivatization Reactions, Wiley, New York, 1979. 

Fluorophores and analytes derivatized with a fluorophoric label [56-105]... 

As can be seen in Table 3, a wide range of analytes derivatized with different labels have been detected using the POCL reaction. Most of these applications have employed flow injection or liquid chromatographic techniques. An area of growing interest is the combination of capillary electrophoresis with chemiluminescence. Several strategies have been used to detect analytes with fluorescent... 

In principle, all of the methods for selective oxidations of di- and polyenes28 can be employed for analytical derivatization. However, the complexity of products obtained rules out some of these. Despite this, epoxidation of selected double bonds is used for comparison of spectra (see previous discussion on MS). Epoxidation of isolated non-conjugated... 

Rosenfeld, J. M., Recent Developments in the Chemistry and Application of Analytical Derivatizations, In Sampling and Sample Preparation for Field and Laboratory Fundamentals and New Directions in Sample Preparation, Pawliszyn, J., Ed., Vol. XXXVll, Elsevier Science, Amsterdam, Netherlands, pp. 609-668, 2002. 

Brede, C., Skjevrak, I. and Herikstad, H. (2003). Determination of primary aromatic amines in water food simulant using solid-phase analytical derivatization followed by gas chromatography coupled with mass spectrometry, J. Chrom. A, 983, 35-42. 

Knapp, K. R. "Handbook of Analytical Derivatization Reactions" John Wiley and Sons New York, 1979 p. 267. 

Analytical chemistry applied to foods widely uses separation techniques in order to characterize foods on the basis of their major and minor constituent compounds. The minor compounds often highlight important differences rather than the major compounds. Chromatographic techniques have been widely applied however, when only gas chromatography (GC) was available, the application of this technique was severely limited by the thermal stability of the analytes. Derivatization reactions are able to somewhat protect organic molecules from degradation, but generally these procednres are rather time consuming and, sometimes, artifacts could be formed. 

Polar and ionic analytes can be extracted from a variety of sample matrices using in-situ chemical derivatization under SFE conditions followed by SFE extraction of the derivatized analytes. Derivatization of the analytes during a... 

Analyte derivatization is commonplace, particularly for chromatographic separation. Derivatization serves mainly three purposes in this context.124... 

In the ideal case, all the three objectives can be combined. Common examples are the derivatization of polar or ionic analytes for GC. In the case of organic analytes, molecules with active H atoms have to be derivatized in order to prevent the formation of hydrogen bonds between analyte molecules, which reduces their volatility or may even lead to thermal decomposition before volatilization. In the case of ionic organometallic analytes, derivatization may involve, for example, hydridization or alkylation, so that the ionic species can be transformed into neutral and thus volatile ones. 

Analyte derivatization has been the subject of a large number of books, book chapters, and... 

Rosenfeld, J.M. 1999. Solid-phase analytical derivatization Enhancement of sensitivity and selectivity of analysis. J. Chromatogr. A 843 19-27. 

CWC-related chemicals in aqueous liquid samples (water samples) are usually recovered by extraction with an organic solvent. Modem methods such as SPE and solid phase micro extraction (SPME) have also been presented 04 24). Organic extractions and these modem methods mainly recover nonpolar CWC-related chemicals, but leave behind the water-soluble and nonvolatile chemicals. These must also be recovered, however, because the agents tend to decompose (hydrolyze) rapidly under conditions in the environment. In the past few years, techniques such as CE and LC, relying on element specific or mass spectrometric detection, have been intensively developed to provide easy and effective ways of recovering these chemicals from water samples with only minor sample preparation (2S 44,1. For GC/MS analysis, the water must be displaced and the analytes derivatized. 

ANALYTICAL DERIVATIZATION FOR GAS CHROMATOGRAPHY/ MASS SPECTROMETRIC ANALYSIS... 

In addition to an increase in the volatility of the analytes, derivatization may also bring about an enhancement in the sensitivity of detection. This is particularly relevant with fluorine-containing reagents (perfluorobenzylation, trifluoroacetylation, heptafluorobutylation), followed by GC/MS analysis under electron-capture negative-ion Cl conditions. 

There are a number of reasons why derivatization of samples is necessary. First, the hydroxide and carboxylic moieties may form hydrogen-bonds in the gas phase, thus resulting in poor chromatography. Secondly, the compounds may sorb onto the chromatographic system, resulting in poor chromatography performance, peak shape, and in the case of very low concentrations, non-detection of the analytes. Furthermore, it is known that -tetrahydrocannabinol carboxylic acid thermally decarboxylates at temperatures above 110-120° C, and converts into A -tetrahydrocannabinol. While in some laboratories this is assumed to be quantitative, this may not always be the case. Derivatization will allow determination of both the A -tetrahydrocannabinol and its carboxylic acid. In addition, in the case of very low concentrations of analytes, derivatization will improve the limits of determination and quantification. 

KNAPP, D.R., 1979, Flandbook of analytical derivatization reactions (New York, John Wiley Sons). 

The enantiomeric purity or composition of drugs, synthetic intermediates, analogs, etc., in bulk samples can be determined via chiral derivatiza-tion in laboratory research, manufacturing processes, dosage forms, quality control, etc. In these applications, limitations on the amount of material available are usually nonexistent, allowing for convenient derivatization and ready detection. In such derivatizations, 0.1-1.0 mg is typically the amount of analyte derivatized. 

While analytical derivatizations are an effective way for extracting compounds, these often require additional steps in the analytical procedure and can introduce side products that may interfere with the analysis. Solid phase extraction has provided an alternative method to this process. The advantage of solid phase extraction is that the reagents, derivatives, and side products are maintained on the solid phase. As needed, these derivatives and side products can be selectively eluted after the desired derivative has been formed on the column. In addition, this method can eliminate potential problems associated with emulsion formulation that may occur with liquid-liquid extraction of compounds from the biological matrix. Finally, solid phase extraction is easily amenable to automation with other analytical detection methods such as gas and liquid chromatography. The phases used in solid phase extraction are the standard ones employed in other extraction methods. ... 

As noted earlier for the extraction of BTX compounds and shown in Fig. 4.28, coating/sample partition coefficients depend largely on the type of coating for a given analyte. Derivatization and temperature also have some influenee on selectivity and must be adjusted as a funetion of the analytes, matrix and state of the sample. 

MS is a universal detector for LC Analysis of thermolabile analytes, not amenable to GC-MS Analysis of nonvolatile analytes Avoid analyte derivatization MS affords a low detection limit (<10g) Identification of the analytes Assessment of peak purity... 

ESI is best described as a mixed-mode ionization, where various processes contribute to the final result. The soft-desolvation and lEV models indicate the importance of generating preformed analyte ions in solution. For most analytes with basic functions, e.g., amines and amides, or acidic functions, e.g., carboxylic acid or aromatic phenols, preformed ions can be produced by the selection of an appropriate pH of the mobile phase. For basic compounds, acidic mobile-phase conditions ate selected, and basic conditions for acidic compounds. Analyte derivatization has been described to introduce a basic site or a fixed charge from a quaternary ammonium group in analytes that lack such properties. 

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