Hyphenated MS techniques

Dalbergia odorifera Heartwood Flavonoids, isoflavonoids ESI(-) Liu etal, 2005 

Lupinus albus, L. angustifolius, L. luteus Root Flavonoid glycosides, isoflavonoid glycosides (O-linked and C-linked) ESI( ) Kachlicki et cd. 2005, 2008 Muth eta/., 2008  

Medicago truncatula Root and cell culture Flavonoids, isoflavonoids (glycosides) ESI( ) Farag / al., 2007 

Sophora flavescens Root Flavonoids, isoflavonoids ESI (H-) Zhang et al, 2007 

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Table 3 presents an overview of so-called hyphenated MS techniques, with their individual suitability and features. 

B. Le Bizec, P. Marchand, D. Maume, F. Monteau, F. Andre, Monitoring anabolic steroids in meat-producing animals. Review of current hyphenated MS techniques, Chromatographia, S59 (2004) S3. 

Since the advent of hyphenated MS techniques, gas chromatography (GC)-MS in the 1980s and LC-MS in the 1990s autosamplers have become a necessity at the front of MS-based instrument systems. Indeed the autosampler is a critical component of any modem LC-MS-based analysis system. Autosamplers have evolved to meet the increased demand requirements of automated well-based MS analysis. The primary figures of merit for autosampling devices are robustness, speed, lack of memory effect, swept volume, plate capacity, integration with MS software, and flexibility ... 

Coupling of analytical techniques (detectors) to high-performance liquid chromatographic (HPLC) systems has increased in the last tree decades. Initially, gas chromatography was coupled to mass spectrometry (MS), then to infrai ed (IR) spectroscopy. Following the main interest was to hyphenate analytical techniques to HPLC. 

In the deformulation of PE/additive systems by mass spectrometry, much less fragmentation was observed with DCI-MS/MS using ammonia as a reagent gas, than with FAB-MS [69]. FAB did not detect all the additives in the extracts. The softness and the lack of matrix effect make ammonia DCI a better ionisation technique than FAB for the analysis of additives directly from the extracts. Applications of hyphenated FAB-MS techniques are described elsewhere low-flow LC-MS (Section 7.3.3.2) and CE-MS (Section 7.3.6.1) for polar nonvolatile organics, and TLC-MS (Section 7.3.5.4). 

Applications of hyphenated LSIMS techniques are described elsewhere, e.g. TLC-MS (Section 73.5.4). 

FD-MS is a very effective technique for determining molecular weights of thermally labile and nonvolatile compounds, such as polymer additives which do not give good molecular ion spectra during electron impact or chemical ionisation [108], In order to enhance the structural information of the technique, MS/MS approaches must be used [96], Hyphenated chromatography-FD/FT-MS techniques appear to be restricted to on-line GC-MS. 

Principles and Characteristics The main reasons for hyphenating MS to CE are the almost universal nature of the detector, its sensitivity and the structural information obtainable, including assessment of peak purity and identity. As CE is a liquid-phase separation technique, coupling to the mass spectrometer can be achieved by means of (modified) LC-MS interfaces. Because of the low flow-rates applied in CE, i.e. typically below lOOnLmin-1, a special coupling device is required to couple CE and the LC-MS interface. Three such devices have been developed, namely a... 

Coupled (hyphenated) analytical techniques of a separation method and a method of analytical determination, e.g. GC-MS, see Fig. 3.13, by which higher-dimensional signal functions are obtained. Strictly speaking, the dimension is 2(n + 1) in the case that n mass spectra are recorded. 

Hyphenated analytical techniques such as LC-MS, which combines liquid chromatography and mass spectrometry, are well-developed laboratory tools that are widely used in the pharmaceutical industry. Eor some compounds, mass spectrometry alone is insufficient for complete structural elucidation of unknown compounds nuclear magnetic resonance spectroscopy (NMR) can help elucidate the structure of these compounds (see Chapter 20). Traditionally, NMR experiments are performed on more or less pure samples, in which the signals of a single component dominate. Therefore, the structural analysis of individual components of complex mixtures is normally time-consuming and less cost-effective. The... 

Numerous papers have relied on only UV-visible spectra for their identification of phenolics, but for positive identification purposes, HPLC-mass spectrometry (MS) is another detection mode that can provide detection of all phenolic compounds in foods. This technique involves a hyphenated instrument that uses a mass spectrometer as a detector for HPLC or uses HPLC as cleanup step for mass spectrometry. After preparative HPLC, the MS technique has frequently been employed for structural identification of phenolics in many foods and essential oils because of its sensitivity and selectivity and its ability to provide structural information. 

Hyphenated chromatographic techniques of various types (e.g., HRGC/HRGC and HPLC/HRGC) are being used in conjunction with a variety of detectors to improve detectability, increase specificity, and reduce cleanup costs for routine analysis. Vuruls et al. (1992) reported ng/L quantitation for aqueous atrazine samples by LC/GC/MS. 

The thermal characterisation of elastomers has recently been reviewed by Sircar [28] from which it appears that DSC followed by TG/DTG are the most popular thermal analysis techniques for elastomer applications. The TG/differential thermal gravimetry (DTG) method remains the method of choice for compositional analysis of uncured and cured elastomer compounds. Sircar s comprehensive review [28] was based on single thermal methods (TG, DSC, differential thermal analysis (DTA), thermomechanical analysis (TMA), DMA) and excluded combined (TG-DSC, TG-DTA) and simultaneous (TG-fourier transform infrared (TG-FTIR), TG-mass spectroscopy (TG-MS)) techniques. In this chapter the emphasis is on those multiple and hyphenated thermogravimetric analysis techniques which have had an impact on the characterisation of elastomers. The review is based mainly on Chemical Abstracts records corresponding to the keywords elastomers, thermogravimetry, differential scanning calorimetry, differential thermal analysis, infrared and mass spectrometry over the period 1979-1999. Table 1.1 contains the references to the various combined techniques. 

Table 1.4 shows that the most numerous applications of hyphenated thermogravimetric techniques for the study of elastomeric material make use of TG-DTA, followed by TG-FTIR, TG-DSC, TG-MS and TG-DTA-MS, with only occasional recourse to TG-DSC-MS and TG-GC-MS. Table 1.5 indicates the general performance characteristics of the thermogravimetric techniques in use for the study of elastomeric materials. 

Both Soderstrom et al. (25) and Creasy et al. (26) have applied GC/FTIR together with several other hyphenated chromatographic techniques to analyze CWC-related chemicals in complex matrices. The results of the different technique have been combined to unequivocally identify the relevant chemicals in low concentrations. In both studies, IR and MS spectra have been used together in spectral interpretation. Weimaster et al. (70) studied samples collected in Iraq, using a very wide variety of instrumentation, but they could not find any scheduled chemicals. 

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