Derivatized Species

2 Derivatized Species By exploring the specific reactivity of the primary amine group, derivative methods including with Fmoc chloride and 4-(dimethylamino)benzoic acid have been developed to enhance the analysis of PE species [44—46]. The enhancement of ionization efficiency in the negative-ion mode is achieved after derivatization through turning weakly anionic lipids (or weakly zwitterionic lipids) into anionic lipids (Chapters 2 and 3). 

As discussed in Chapter 2, ionization of anionic GPL species in the positive-ion mode is not favorable, but still can be formed in the presence of alkaline ion(s) in the solution or under acidic conditions. Generally, the sensitivity for ionization as alkaline adducts is markedly lower than what is observed as the [M-FH]+ ions in the positive-ion mode. Characterization of lithium and dilithium adducts of PI species (i.e., [M-FLi]+ and [M-H-l-2Li] ) or their protonated species has been performed [1]. 

PI species can be readily ionized as deprotonated form. The fragmentation pattern of deprotonated PI species ([M-H] ) is very informative and more complicated than those of other anionic GPLs [41]. The fragmentation pattern of deprotonated PI species contains the following fragments  

The fragmentation pathways of deprotonated phosphatidylinositol phosphate (PIP) and diphosphate (PIP2) species (i.e., [M-H] ) after low-energy CID are similar to that of PI [41]. However, the doubly charged (i.e., [M-2H] ) ions of PIP and PIP2 species undergo fragmentation pathways that are similar to that of 

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With 100 ng of cortisone only [M + Ag]+ is observed. The SIMS spectra of derivatized cortisone, on the other hand, show a single peak corresponding to the molecular ion of the derivatized species and an ion of low abundance corresponding to the same fragmentation observed for the underivatized species. The derivatized cortisone was detected at 10 ng with the same signal-to-noise ratio as that for 100 ng of underivatized cortisone, which is approximately an order of magnitude improvement in the detection sensitivity. 

We have implemented scanning methodologies using MALDI-TOF mass spectrometry to partially purified venom from C. striatus and C. ermineus. We have carried out specific derivatizations in order to deduce composition and sequence information. Together with an intact mass these measurements are used to determine whether an ionized species observed in the MALDI mass spectrum corresponds with the intact protonated molecule of a previously characterized conotoxin. The information obtained from derivatizations is also important when the ionized species does not correspond with the intact mass of peptides of known sequence. In that case, post source decay of the native and derivatized species may help assign the fragment ions. 

Postcolumn derivatization with absorbance spectroscopy Postcolumn derivatization reactions involve the chemical reaction of the analyte with a chromophore, after the analyte has passed through the column, followed by the detection of the analyte by UV-Vis absorbance spectroscopy. This type of detection system is typically used for transition and lanthanide metal cations due to the incompatibilities between the transition metal complexing eluent and the conductivity supressor. The properties of the postcolumn derivatization species should include high molar absorptivity of complexes, reactivity with most metals, formation of stable metal com-... 

Nowadays, atomic absorption spectrometry (AAS) systems are comparatively inexpensive element selective detectors, and some of the instruments also show multi(few)-element capability. There are flame (F AAS), cold vapor (CV AAS), hydride-generating (HG AAS), and graphite furnace (GF-AAS) systems. However, the use of AAS-based detectors for on-line speciation analysis is problematic. F AAS is usually not sensitive enough for speciation analysis at "normal" environmental or physiological concentrations and sample intake is high (4—5 ml/min), which complicates on-line hyphenations with LC an auxiliary flow is necessary. CV AAS and HG AAS use selective derivatization for matrix separation and increased sensitivity for the derivatized species. But, the detector response is species dependent and interferences can be a problem. GF AAS requires only a few microliters of sample and provides low detection limits, between 0.1 and 5 gg/1. Matrix interferences are widely eliminated by Zeeman correction and matrix modifiers nevertheless, quantification errors were reported as atomization temperature does not exceed 2900°C. The most critical problem in respect to speciation analysis is the discontinuous measiuement because of the temperature program operation employed, which takes a few minutes. Therefore, GF AAS is unsuitable for on-line hyphenations as chromatograms carmot be monitored with sufficient resolution. 

Anions of another group were derivatized with formation of gaseous chemiluminescing species. Chemical reaction - gas extraction has been used with chemiluminescence detection in the stream of canier gas in on-line mode. Rate of a number of reactions has been studied as well as kinetic curves of extraction of gaseous products. Highly sensitive and rapid hybrid procedures have been developed for the determination of lO, BrO, CIO, CIO, NO,, N03, CrO, CIO, Br, T, S, 803 with detection limits at the level of pg/L, duration of analysis 3 min. 

Accordingly, the resulting current reflects the rate at which electrons move across the electrode-solution interface. Potentiostatic techniques can thus measure any chemical species that is electroactive, in other words, that can be made to reduce or oxidize. Knowledge of the reactivity of functional group in a given compound can be used to predict its electroactivity. Nonelectroactive compounds may also be detected in connection with indirect or derivatization procedures. 

Figure 48 Cage cleavage of T8[c-C5H9]8 and T8[c-C6Hn]8 and derivatization of trisilanol species.

In 1975, the fabrication of a chiral electrode by permanent attachment of amino acid residues to pendant groups on a graphite surface was reported At the same time, stimulated by the development of bonded phases on silica and aluminia surfaces the first example of derivatized metal surfaces for use as chemically modified electrodes was presented. A silanization technique was used for covalently binding redox species to hydroxy groups of SnOj or Pt surfaces. Before that time, some successful attemps to create electrode surfaces with deliberate chemical properties made use of specific adsorption techniques... 

Fluorescence analysis has been extended to many nonfluorescent species by the development of a wide range of derivatizing agents that form a fluorescent product. This approach has been especially useful with biochemical molecules, many of which are not natural fluorophores. 

In general, a nonspecific method is not acceptable because it is possible for the identity of the source of the analyte to be called into question. However, in cases where derivatization from a common species is the only method available (e.g., dithio-carbamate compounds), the use of a nonspecific common moiety method may be acceptable. 

Complex (51b) was prepared according to Equation (11). The dangling formyl groups can be used for further derivatization (e.g., (517) shown in Figure 16), and (516) serves as a valuable starting material for the synthesis of macrocyclic dinuclear species (compare Section 6.3.4.12).1367... 

Utilizing the difference in selectivity between a monolithic silica-C18 column (2nd-D) and another particle-packed column of C18 phase (lst-D), 2D HPLC separation was shown mainly for basic compounds and other species (Venkatramani and Zelechonok, 2003). The authors also reported other examples of reversed-phase 2D HPLC, using amino- and cyano-derivatized particle-packed columns for 2nd-D separation. The combination of normal-phase separation for the 1 st-D and reversed-phase separation on monolithic Ci g column for the 2nd-D was reported (Dugo et al., 2004). The use of a microbore column and weak mobile phase for the lst-D and a monolithic column for the 2nd-D was essential for successful operation. Improvement in the 2D separation of complex mixtures of Chinese medicines was also reported (Hu et al., 2005). Following are practical examples of comprehensive 2D HPLC using monolithic silica columns that have been reported. 

In a specific example in the same paper [17], one polymer contained triphenyl-methane fragments and the other o-nitrophenol moieties (A and B, respectively, in Scheme 5.1). The triphenylmethane residues were reacted with an alkyllithium and converted to surface-confined trityllithium species. This derivatized polymer was then mixed with an excess of the second polymer and the combination was used in the stoichiometric benzoylation of y-butryrolactonc (Scheme 5.2) or of phenylace-tonitrile (Scheme 5.3). The procedure was also demonstrated successfully using solid sodium hydride instead of the lithiated polymer. 

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