Belt transport interface

In reduced-flow LC-MS systems, the solvent flow into the spectrometer is reduced to a level where the pumping system can cope. Essentially, three such systems have been developed direct-liquid-introduction (DLI), flowing FAB [531] and electrospray [532]. An alternative approach to belt transport interfacing is to deliver the column eluate directly into the MS source and use Cl techniques. Methods based on this principle are called direct-liquid-injection systems, which are comprised of capillary flow restrictors, diaphragms,... 

The Spray Deposition Device for Belt Transport Interfaces... 

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. ... 

For LC/MS the main problem is the large amount of mobile liquid phase that must be removed to get the effluent reduced to the high vacuum of the MS. Microbore columns are desirable for this reason.22 The three most popular devices have been summarized by Majors23 direct liquid interface (DLI), moving belt transport, and thermospray.24 The thermospray device consists of a small bore capillary tube that is heated to produce a stable, high-velocity jet consisting mostly of vapor with a small amount of mist. It not only provides an interface to the MS, it also causes the ionization of analytes necessary for the MS. Some think it may find more widespread use as a transport device. 

The scientific curiosity to explore the utility of mass spectrometry to compounds that could not be analyzed by conventional GC/MS was supported by the need to extend the technique into the expanding field of biochemistry. While the development of LC/MS is still undergoing rapid evolution as evidenced by the number of reviews published at regular intervals, three main technological approaches have been constructed which continue to gain popular acceptance for practical use. These three introduction interfaces that are available commercially are the moving belt or transport interface (MB1), direct liquid introduction (DLI), and thermospray (TSP). This review will concentrate on these three interface types that are currently in widespread use. 

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]. 

Moving belt interface. This solute(s) is deposited after HPLC onto a moving belt, HPLC solvents being flash evaporated. The belt transports... 

Later it was found that the polluting lubricant droplets originating from the transport belts used in the production they had fallen into the paint bath and prevented adhesion of the paint to the metal. It can be concluded that the high sensitivity of SSIMS in the detection of submonolayer coverage of organic species makes it an extremely powerful tool for solving such interface problems. 

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. 

Scott et al. [53] and McFadden et al. [54] first described this mechanical interface in 1974 and 1976. A diagram of a commercialized moving belt interface is shown in Fig. 19.11. The interface first consisted of a spool of wire, which was unrolled off one spool and onto another. As the wire was wound from spool to spool, the effluent from a liquid chromatographic separation was applied to the wire. As the wire was transported through... 

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 %. 

In contrast with the limited ability to reconfigure conveyor belt systems and their limited ability to handle different sized specimen containers, mobile robots are easily adapted to carry various sizes and shapes of specimen containers,. and can be reprogrammed to travel to new (and distant) locations with changes in laboratory geometry. Limitations of mobile robots include their requirement of having to batch specimens, and their difficulty in interfacing mechanically with laboratory analyzers so that specimens are introduced directly from the mobile robot onto the analyzer. In many situations, laboratory personnel are still required to place specimens onto or remove specimens from the mobile robot at each stopping place. Mobile robots have been used to return conveyor belt specimen carrier racks to the central dispatch area and for transport of specimens within and outside the laboratory. In the latter application, mobile robots may be a useful alternative to pneumatic tube defiv-ery systems. 

When assembly at a workstation is impossible for technological or economical reasons, the assembly can be carried out with several chained manual assembly stations (Lotter 1992). Manual assembly systems consist of a multiplicity of components, as shown in Figure 20. The stations are chained by double-belt conveyors or transport rollers. The modules rest on carriers with adapted devices for fixing the modules. The carriers form a defined interface between the module and the... 

There have been numerous successful approaches to LC/MS, ranging from mechanical transport of solute to the mass spectrometer after external solvent removal (belt/wire systems and parhcle-beam interfaces) to bulk soluhon introduchon (with or without splitting) involving nebulizahon and ionization direcly from the solvent stream. However, LC/MS has been surprisingly underutilized for the characterization of synthetic polymers despite its apparent advantages over the direct application of mass spectrometry. 

Gas chromatography (GC) and MS have long been used in conjuction, as we have repeatedly mentioned. However, GC is not suitable for the separation of glycerides and other complex lipids, because these molecules are thermolabile. Liquid chromatography provides a suitable substitute for MS lipid analysis (Fig. 9.35). Techniques for coupling LC with MS have been reviewed by Privett and Erdahl (1978) these authors have also described an interface for the analysis of lipids by MS. This interface is based on the moving wire transport principle using an endless stainless-steel belt (Erdahl and Privett, 1977). After evaporation of the solvent, the solute remains as a... 

Other LC-MS ionization techniques are available but their utility for clinical research is low. Until the advent of ESI and APCI the most popular LC-MS interface was thermospray. Other techniques used with varying degrees of success included flow-FAB, transporter belts, and particle beam interfaces. These have been almost wholly superseded by ESI and APCI. 

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