Transport systems moving belt

Various transport type interfaces, such as SFC-MB-MS and SFC-PB-MS, have been developed. The particle-beam interface eliminates most of the mobile phase using a two-stage momentum separator with the moving-belt interface, the column effluent is deposited on a belt, which is heated to evaporate the mobile phase. These interfaces allow the chromatograph and the mass spectrometer to operate independently. By depositing the analyte on a belt, the flow-rate and composition of the mobile phase can be altered without regard to a deterioration in the system s performance within practical limits. Both El and Cl spectra can be obtained. Moving-belt SFE-SFC-MS" has been described. 

Two LC-MS systems were developed, based on nearly full removal of the solvent moving-belt [520] and particle-beam [521], Mechanical transport devices... 

An alternative to direct liquid introduction is the moving belt, or moving-wire, transport interface. Because all l.c. solvents are evaporated before the sample is transported into the ion source, fewer restrictions are placed on solvent type, flow rates, or buffer composition. This system has been used for analysis of mixtures of pentoses, hexoses, and disaccha-rides. ... 

Most of the direct and indirect (transport) interfaces described here use chemical ionization (c.i.) ion-sources, which are not well suited to such polar, non-volatile compounds as tri- and higher oligosaccharides. The thermospray interface, which can operate on an ion-evaporative mode, is capable of producing intact molecular ions from such nonvolatile, polar molecules and should be useful in oligosaccharide analysis. Molecules of this type, however, can also be easily analyzed by fast-atom-bombardment ionization, and use of this technique, coupled to direct liquid introduction and moving-belt interfaces, has been reported. The latter system has been applied to complex oligosaccharide analysis. ... 

J. 2.2.2 Moving Belt System. Initially developed by McFadden et al. [13], the moving belt system was based on the physical method of evaporation of the mobile phase through heat and vacuum that leave analytes as a thin coating on a continuously cycling polyimide belt. The analytes were transported from atmospheric pressure region to the vacuum of the ion source through differentially pumped vacuum locks. Ionization methods used... 

A modified Pye Unicam moving-wire detector was described by Scott et al. [35] in 1974 to fit the vacuum requirements of a mass spectrometer (Figure 3.3). Part of the colunrn effluent is deposited on to a wire, which transports the liquid along a heating element to evaporate the solvents, and through a series of vacuum locks to the ion source where the analyte is thermally desorbed from the wire prior to the ionization. Ionization is independent of the LC system. Therefore, conventional El and Cl spectra can be obtained [35]. This approach was subsequently adapted in 1976 by MacFadden [36] into the moving-belt interface (Ch.4.4). 

Moving Belt Interface (MBI). The concept of transport systems was first demonstrated by Scott et aL (I) who designed a system using a moving wire to carry the solvent/solute into the MS source via two vacuum locks where the vaporization of the solvent was accomplished. Then vaporization of the remaining solute was carried out by passing a current through the wire. The major drawback of this early prototype to transport systems was that the efficiency of the system was a mere %. 

Transport system Segments of a conveyor belt line that move specimens to the appropriate location. 

There are two approaches to transporting material prepared for the press line. Belt conveyors are used for higher density materials, but the mat becomes very bulky when densities fall. For fibres, pneumatic transport systems, where the fibre is carried by a moving stream of air, are used although belt conveyors are used for the moving floor of the fibre bin or bunker and for the conveyors that carry the MDF mat from the former to the press. 

Early interfaces used liquid nitrogen or helium cryogenic techniques to remove the solvent vapour, but these were rather cumbersome and not too efficient. Moving belt transport systems were also one of the first interfaces to be developed incorporating a flash vaporiser to remove the solvent before the sample reached the ion source. The main approaches used today are based on thermospray, atmospheric pressure and particle beam interfacing techniques [10]. 

A belt conveyor is mainly formed by an endless belt translating around two or more rollers. The material is moved by placing it directly on the translating belt. This transportation system can mainly assume two different configurations (Fig. 4) ... 

Engineers design transportation systems to move people or goods in an organized and efficient maimer. Earher in this chapter, you read about an airport as an example of a transportation system. Now consider a different type of transportation system. How are products moved (transported) aroimd a large factory as they are being produced Sometimes they move on a conveyor belt type of system (Figure 2-14). 

Mass detector. The liquid chromatographer s demand for a universal detector which overcomes some of the problems encountered with the RI detector, (such as poor sensitivity and temperature instability) led to the development about ten years ago of the mass detector described here. The transport detectors of the 1960s detected the solute by means of a flame ionization detector after removal of the solvent from the eluent stream. They were abandoned, owing to lack of sensitivity and mechanical problems associated with the moving belt or wire. The new mass detector is similar in principle, but here the eluent leaves the column and is pumped into a nebulizer, assisted by an air supply. The atomized liquid is passed into a heated evaporation column where all the solutes less volatile than the solvent are carried down the column as a cloud of fine particles. A light source and photomultiplier arranged at the bottom of the column, perpendicular to the flow, detect the cloud of particles. The output from the photomultiplier, which is proportional to the concentration, can be amplified and directed to a recorder or data system. 

Van der Weij s (1932) comparison of the transport system with a unidirection-ally moving conveyor belt loaded with different amounts of auxin molecules was a first attempt to conceptualize the basipetal auxin transport mechanism. It is noteworthy that this rather mechanistic picture, which has found little experimental basis, has had something of a revival by assuming plasmalemma-somes to be possible vehicles of auxin transport (Wangermann and Withers 1978 see Fig. 3.7). 

Transport-flame ionisation detectors probably represent the future in HPLC analysis. With such systems, the eluent is entrained on a moving belt and carried through an oven where the solvent is removed, and then in essence into a flame ionization detector, where the separated components are combusted and detected as in a gas chromatograph. A wide range of solvents can be used, and the response is highly rectilinear with respect to mass. Unfortunately, the existing commercial instruments are rather too costly for most analysts, and their reliability has still to be ascertained. 

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