Other Hyphenated Systems

Several other hyphenated systems are LC coupled with infrared spectroscopy (IR) for compound identification and LC couple with inorganic spectroscopy such as atomic absorption (AA) or inductively coupled plasma (ICP) for studies of metal speciation in samples. 

Solid-phase microextraction (SPME) [63] is normally used for sample collection, pre-concentration and desalting before analysis. It is usually used off-line. However, SPME can be implemented in temporal monitoring of biomolecules with low to medium temporal resolution (minutes, hours) [64]. In one method, SPME fibers were used to sample metabolites from live animals followed by analysis using LC-MS [65]. The method enabled extraction of metabolites directly in the tissue of moving animals. It was not necessary to withdraw a representative biological sample for analysis. In this case, the amount of analyte extracted into the SPME fiber was independent of the sample volume [65]. Recently, SPME was also coupled on-line with a MS ion source operated at atmospheric pressure [66]. 

On-line extraction and preconcentration systems are sometimes coupled directly with MS decreasing sample preparation time [67-69]. Cig pipette tips can be used to purify complex samples, and directly introduce them to the mass spectrometer via an ESI interface [70]. This technique is characterized by great simplicity however, one may expect that it may 

Other on-line sample pretreatment methods can be combined with MS directly or before the separation column. For example, on-line hydrogen/deuterium exchange (UDX) could 

From syringe From HPLC Position A pump pump (sample injection) 

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The use of filament-on thermospray LC-MS in environmental pesticide analysis is a valuable technique with points of similarity in the ionization process with other hyphenated systems such as direct liquid introduction (DLI) LC-MS and chemical ionization GC-MS. The relative merits of ammonium formate as ionizing additive in PI and NI modes TSP LC-MS for three different... 

Iodine and Se speciation in breast milk provides an example of the use of CE in hyphenated systems with ICP-MS detection. By employing CE, Michalke and colleagues determined selenoaminocids and identified two chemical forms of iodine, I- and thyroxine, which were present in comparable amounts in milk [115-117]. Other authors used SEC and IEC for I speciation in various types of milk and infant formulae (see Table 8.3) and found I- as the main species, with the exception of breast milk and formulae. The latter were found to contain less I than commercial and human milk, and mostly as an unidentified macromolecular compound. 

There is a pronounced tendency towards coupling flow analysis with other analytical systems. Hyphenation has proved to be an excellent development, as the favourable characteristics of both sub-systems are better exploited [165]. 

Major trends in the future growth of flow analysis are likely to include the evolution of instrument design (including miniaturisation and expert flow systems), the recognition of more flow-based standard methods, hyphenation with other detection systems and an impact on chemical measurements in new and emerging areas of science. 

Hyphenation of flow analysers with other detection systems will become increasingly common, e.g., using flow manifolds for sample conditioning at the front end of other detection systems. 

Analyte identification based only on the retention time of a component is suspect even for simple mixtures. Selective detectors reduce the uncertainty to some extent by detecting only the components sharing a certain characteristic, but these do not eliminate the chance of false identification. On the other hand, spectroscopic techniques provide qualitative information about the analyte which is often specific enough to make the identification of a component certain. It is therefore not surprising that attempts to couple GC with various spectroscopic techniques were undertaken from the early days of GC. Today, combined instruments, often referred to as hyphenated systems, are used routinely, and gradually replace conventional gas chromatographs in many areas. 

The capsaicinoids are extracted using different solvents and more recently ultrasound-assisted extraction [61], extraction by means of supercritical fluids [65], extraction by pressurized liquids [58] and enzymatic extraction [59], and analyzed by HPLC [64,93-95], GC [72-76], hyphenated systems as HPLC-MS [96-100], and GC-MS [77]. Normally the GC methods require derivatization of the compounds to make them sufficiently volatile for determination. There are many other reported papers have been found in the literature for the analytical separation, quantitation, and identification of naturally occurring capsaicinoids in different matrices. Select matrices are discussed here. 

The problem of cross-talk between several microcoils has been solved by Professor Andrew Webb and his coworkers, but application in parallel HP LC-NMR detection has stiU yet to be achieved. For this, adequate NMR instrumentation will be necessary. Parallel HPLC-NMR detection with four microcoils in a hyphenated system will surely be realized within the next few years, and in the longer term a configuration of 16 microcoils in four parallel horizontal detection planes, as introduced by Professor Raftery, will be realized. Besides parallel detection, the capillary technique in principle opens the door for the hyphenation of NMR spectroscopy with other capillary separation techniques such as gas chromatography and supercritical fluid chromatography (SFC). The long spin-lattice relaxation times in the supercritical and gaseous states can be reduced by relaxation agents present in the separation capillary prior to the actual NMR detection. 

The combination of LC and NMR is arguably the most attractive hyphenated system for polymer analysis, as well as in many other fields. NMR may yield a wealth of information on molecular composition and structure (e.g. chain regularity, branching, comonomer sequence see Section 7.4.1). Also, as mentioned in Section 7.4.1, NMR provides excellent opportunities for quantitative analysis. Thus, LC-NMR is a highly desirable proposition for polymer analysis. 

The possibiHties for multidimensional iastmmental techniques are endless, and many other candidate components for iaclusion as hyphenated methods are expected to surface as the technology of interfacing is resolved. In addition, ternary systems, such as gas chromatography-mass spectrometry-iafrared spectrometry (gc/ms/ir), are also commercially available. 

Section 6.4 deals with other EI-MS analyses of samples, i.e. analyses using direct introduction methods (reservoir or reference inlet system and direct insertion probe). Applications of hyphenated electron impact mass-spectrometric techniques for poly-mer/additive analysis are described elsewhere GC-MS (Section 7.3.1.2), LC-PB-MS (Section 7.3.3.2), SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

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