Belt transport, interface with

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. 

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. 

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. 

The slot in the interfaces for passage of the belt is formed by two "L"-shaped sapphire pieces which are attached to the stainless-steel flange or vacuum closure bar by epoxy cement. The belts used are either 0.05 or 0.075 mm thick and the slot tolerance is set to be 0.075 mm greater than the belt thickness (i.e., either 0.125 or 0.15 mm). The belt width is 0.317 cm and the slot width is 0.325 cm. A ribbon 0.32 cm wide travelling at a speed of 2.5 cm/sec will carry away a liquid film 0.2 mm thick from a solvent flow of 1 ml/min and if the solvent film can be evaporated without loss of solute, then the ribbon will transport virtually 100% of the solute into the mass spectrometer. Sample utilization will then depend only on the efficiency of the flash vaporization step. In practice, some sample is lost by spray processes and the flash vaporization cannot be fully efficient for all compounds. Nevertheless, yields in the range of 25-40% have been attained with an LC/MS ribbon interface system. It follows that the quantity of column eluent taken from the ribbon will be twenty times greater than that taken by the wire and provide significantly improved sensitivity. 

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