Tandem introduction system

Computer control of the switching valve to allow the HPLC to be used in tandem with the ICP-MS normal sample introduction system... 

The main advantages of the ms/ms systems are related to the sensitivity and selectivity they provide. Two mass analyzers in tandem significantly enhance selectivity. Thus samples in very complex matrices can be characterized quickly with Htde or no sample clean-up. Direct introduction of samples such as coca leaves or urine into an ms or even a gc/lc/ms system requires a clean-up step that is not needed in tandem mass spectrometry (28,29). Adding the sensitivity of the electron multiplier to this type of selectivity makes ms/ms a powerhil analytical tool, indeed. It should be noted that introduction of very complex materials increases the frequency of ion source cleaning compared to single-stage instmments where sample clean-up is done first. 

The mass spectra of mixtures are often too complex to be interpreted unambiguously, thus favouring the separation of the components of mixtures before examination by mass spectrometry. Nevertheless, direct polymer/additive mixture analysis has been reported [22,23], which is greatly aided by tandem MS. Coupling of mass spectrometry and a flowing liquid stream involves vaporisation and solvent stripping before introduction of the solute into an ion source for gas-phase ionisation (Section 1.33.2). Widespread LC-MS interfaces are thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB), electrospray (ESP), etc. Also, supercritical fluids have been linked to mass spectrometry (SFE-MS, SFC-MS). A mass spectrometer may have more than one inlet (total inlet systems). 

The impact of this new technique, which was called Accelerator Mass Spectrometry (AMS), on the radiocarbon and archaeologist communities, was immediate and revolutionary. The introduction of AMS is indeed recognized by some as the third revolution in radiocarbon dating[22,23] and it has provided the opportunity to date very precious finds by collecting very small samples. The interest in developing the technique of AMS was so evident that, just few years after the measurements cited above, a first dedicated AMS system (based on a tandem accelerator) was designed and built [24] then, the first dedicated... 

Snieckus synthesis85 involves an application of his ingenious tandem directed metallation reaction, which provides a one-step construction of the ellipticine ring system. Introduction of the remaining carbon atoms by the reaction of the quinone (120) with methyl-lithium, and removal of the protecting group, then gave ellipticine (119) in an overall yield of 40% (Scheme 16). 

As noted earlier, the development of the dual cell (37), tandem quadrupole-FTMS (46, 47) and external ionization cell (48, 49) has facilitated the coupling of FTMS and chromatographic methods. Advances in interfacing separation techniques with FTMS will be important in the analysis of mixtures, especially where high mass resolution is required. For example, liquid chromatographic introduction of mixtures isolated from biological systems directly into an FTMS for analysis would eliminate the need for laborious sample clean up. 

The developments in instrumentation include production of dedicated machines. For example, with the introduction of the Attomole 2000 , HVEE (High Voltage Engineering Europe B. V., P.O. Box 99,3800 AB Amersfoort, The Netherlands, Phone +31 33 4619741 Fax +31 33 4615291) has made available a compact C Isotope Ratio Mass Spectrometer ( C IRMS) for biomedical applications. The system provides C/ C ratios down to 10 from sub-milligram samples in typically a few minutes. Both solid samples (carbon) as well as CO, can be analyzed. The Attomole 2000 combines a compact instruments package with the extreme sensitivity of large tandem accelerators that are normally found in big research centres. 

The application of PAT for tabieting has spurred the introduction of systems such as the Tandem (Bruker Optics), which is available for use during tablet production to measure tablet weight, thickness, hardness, and diameter as well as online NIR content uniformity. The system can provide online analysis for the drug... 

The introduction of the open-tubular columns eliminated the need for concentrating devices as the mass spectrometer pumping system could cope with the entire column eluent. Consequently, the column eluent could be passed directly into the mass spectrometer and the total sample can enter the ionization source. The first mass spectrometer used in a GC-MS tandem system was a rapid-scanning magnetic sector instrument that easily provided a resolution of one mass unit. Contemporary mass spectrometers have vastly improved resolution and the most advanced system (involving the triple quadrupole mass spectrometer) gives high in-line sensitivity, selectivity, and resolution. 

Evidently, although the system tolerates both aromatic and aliphatic aldehydes, the introduction of an electron-withdrawing substituent on the aromatic substrate results in a decreased yield. To gain information about the mechanism of the overall tandem reaction, kinetic studies were carried out to identify the rate-determining step. Changing the catalyst concentration in the reaction between 3-methylbutyraldehyde, nitromethane and dimethyl malonate revealed that the reaction is first order in nickel catalyst, indicating that the Michael addition of dimethyl malonate to the nitroalkene is the ratedetermining step. 

Dual columns — The introduction of capillary columns brought about a revolution in the level of resolution, and these columns are now almost universally used. Nonetheless, no single column is able, for example, to resolve all of the 209 PCB congeners so that the application of two columns in tandem with separate ovens and detector systems has been advocated. Fraction cuts from one column are quantitiatively transferred to the other (Duinker et al. 1988). A few examples are given as illustration. 

Expert flow systems take advantage of iterative control devices which work in tandem and permit real-time alterations of the experimental parameters. They are designed to provide decisions for the real-time introduction of correction factors and, eventually, manifold self-optimisation. Enhanced system versatility and flexibility are also achieved. 

Alternatively, the recent introduction of EDESI-MS/MS provides another useful tool for analysing such systems. Tandem mass spectrometry (MS/MS) allows selection of a single ion using one mass analyser then introducing it to a collision cell. Energetic collisions with an inert gas in this cell cause fragmentation of the ion and a daughter ion spectrum is obtained. MS/MS techniques are especially useful for the analysis of complex mixtures, but their application to molecules... 

However, parameters with regard to vehicle characteristics (the type of tyres, introduction of more than three axle systems, vehicle suspension, vehicle dynamics, etc.) have changed ever since the AASHTO experiment or the European experiments have been executed. Research studies carried out by Bonaquist (1992) and Huhtala and Pihlajamaki (1992) have shown that the use of new wide-based single tyres (445 or 385/65R 22.5 and 350/75R 22.5 types) and the use of different types of trucks have a greater damaging effect than conventional tandem axles. 

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