Moving belt coupling

Different methods are used to tackle these problems [10-13], Some of these coupling methods, such as moving-belt coupling or the particle beam (PB) interface, are based on the selective vaporization of the elution solvent before it enters the spectrometer source. Other methods such as direct liquid introduction (DLI) [14] or continuous flow FAB (CF-FAB) rely on reducing the flow of the liquid that is introduced into the interface in order to obtain a flow that can be directly pumped into the source. In order to achieve this it must be reduced to one-twentieth of the value calculated above, that is 5 pi min. These flows are obtained from HPLC capillary columns or from a flow split at the outlet of classical HPLC columns. Finally, a series of HPLC/MS coupling methods such as thermospray (TSP), electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) can tolerate flow rates of about 1 ml min 1 without requiring a flow split. Introducing the eluent entirely into the interface increases the detection sensitivity of these methods. ESI can accept flow rates from 10 nl min-1 levels to... 

Flow limitations restrict application of the DFI interface for pSFC-MS coupling. pSFC-DFI-MS with electron-capture negative ionisation (ECNI) has been reported [421], The flow-rate of eluent associated with pSFC (either analytical scale - 4.6 mm i.d. - or microbore scale 1-2 mm, i.d.) renders this technique more compatible with other LC-MS interfaces, notably TSP and PB. There are few reports on workable pSFC-TSP-MS couplings that have solved real analytical problems. Two interfaces have been used for pSFC-EI-MS the moving-belt (MB) [422] and particle-beam (PB) interfaces [408]. pSFC-MB-MS suffers from mechanical complexity of the interface decomposition of thermally labile analytes problems with quantitative transfer of nonvolatile analytes and poor sensitivity (low ng range). The PB interface is mechanically simpler but requires complex optimisation and poor mass transfer to the ion source results in a limited sensitivity. Table 7.39 lists the main characteristics of pSFC-PB-MS. Jedrzejewski... 

Table 7.46 shows the LC-FTIR interface detection limits. Detection limits approaching those for GC-FHR light-pipe interfaces have been reported for flow-cell HPLC-FTIR when IR-transparent mobile phases are employed. For both the moving-belt and thermospray LC-MS couplings the detection limits are in the ng range. Selective evaporation consisting of fraction collection followed by DRIFT identification achieves a detection limit of 100 ng. 

Coupling of liquid chromatography to mass spectrometry has not only led to a wide variety of interfaces, but also initiated the development of new ionization methods. [8-13,62] In retrospect, the moving belt interface seems rather a curiosity than a LC-interface. The LC effluent is deposited onto a metal wire or belt which is heated thereafter to desolvate the sample. Then, the belt traverses a region of... 

Many interfaces have been developed to meet these demanding challenges. Some of these coupling methods, such as the moving belt or the particle beam interface, are based on the concomitant elimination of the solvent before it enters the mass spectrometer. Other methods such as direct liquid introduction (DLI) or continuous flow FAB rely on splitting the flow of the liquid that is introduced into the interface in order to obtain a flow that can be directly infused into the ionization source. However, these types of interfaces can only handle a fraction of the liquid flow from the LC. 

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. ... 

The first approaches to the coupling of liquid-phase separation techniques with mass spectrometry were designed for HPLC needs, starting in the 1970s with since-forgotten techniques such as direct liquid introduction (DLI) and moving belt. In the 1980s, techniques such as thermospray, continuous-flow-fast atom bombardment (CF-FAB), and particle beam arose. 

The analysis of steroids is a challenging task. GC-MS has frequently been applied, but requires analyte derivatization [1]. Therefore, over the years most LC-MS interfaces have been tested or applied in the analysis of steroids. As early as 1981, Henion [2] demonstrated the analysis of dexamethasone and cortisone with micro-LC coupled to a capillary-inlet interface. Van der Greef et al. [3] described the quantitation of progesterone in serum using isotope dilution MS in anunonium Cl mode using the moving-belt interface. Henion and coworkers [4] described... 

However, the great improvement to solve the possibility of coupling HPLC to MS was the development of interfaces that allow the elimination of the solvent and the vaporization of the solute before this can be analyzed in the mass spectrometer. Several interfaces are now available, such as continuous flow FAB (CF-FAB), thermospray (TSP), moving belt (MB), direct liquid introduction (LDI), and atmospheric pressure ionization (API) in the field of API, three different, but fundamentally similar, techniques are available ion evaporation, electrospray, and ion spray. In each case, the removal of... 

Nevertheless, Figure 5 demonstrates that the enantiomeric separation using a phosphate buffer in the mobile phase can be coupled via the PSS approach on-line to an LC/MS moving belt interface. Other examples of the PSS approach or similar procedures with other compounds and other LC/MS interfaces have been described (2, 9-14). Besides the actual phase-system switching, which enables the choice of the most favorable solvent for a particular interface, the PSS approach offers some other features as well. The desorption flow-rate used can be adjusted to the capabilities of the LC/MS interface applied. While in the present example with the moving belt a flow-rate of 0.4 ml/min of methanol was used, desorption has also been demonstrated with 1.2 ml/min for a thermospray interfaced),... 

Figure 5.5. Moving-belt interface for LC/MS coupling. (Reproduced from ref. 6 by pra-mission of Wiley-Interscience, copyright 1997.)...

P. Arpino, Combined liquid chromatography mass spectrometry I Coupling by means of a moving belt interface. Mass Spectrom. Rev. 8, 35-55 (1989). 

MS has been used with LC (moving belt interface), though not as extensively as with GC. Atmospheric pressure chemical ionization and pneumatically assisted electrospray mass spectrometry coupled to LC have been used for PAC analysis. Since it is easy to collect fractions continuously from LC, bioassays of the collected fractions can be performed and a muta-chromatogram (a plot of mutagenic potency versus fraction number) obtained. 

SEC suffers from poor resolution and low sensitivity [5], while GC is limited by the high molecular weight and polar nature of many antioxidants and light stabilisers, which are designed to be reactive and so decompose when exposed to heat [9]. HPLC the most widely used instrumental method also has limitations [10-12]. HPLC lacks a simple sensitive universal detector that is compatible with all liquid mobile phases. UV or fluorescence detectors, which are commonly used, require that additives have a chromophoric moiety, while the universal refractive index detector only functions under isocratic conditions. As a result, Vargo and Olson have coupled HPLC with mass spectrometry (MS) for this type of application by using a moving belt interface [13]. 

A variety of interfaces was developed for on-line LC-MS coupling. A number of these found wide application when they became commercially available, e.g. the moving-belt interface, direct-liquid introduction, thermospray, particle-beam and continuous-flow fast-atom bombardment (Cf-FAB), but are hardly used any longer due to the introduction of interfaces based on atmospheric-pressure ionization (API), i.e. electrospray and atmospheric-pressure chemical ionization (APCI). Before discussing the API-based interfaces in detail, brief attention is given to three of the older LC-MS interfaces. 

Reciprocating compressors are available with a large variety of other drivers, which include the piston engine, steam turbine, or, in rare cases, a gas turbine. Next in popularity to the electric motor is the piston engine. The arrangement lends itself to skid mounting, particularly with the semi-portable units found in the oilfield. The unit is also popular as a lease unit, which may be lifted onto a flat bed trailer and moved from one location to another as needed. The engine is either direct-coupled or. as with smaller compressors, it may be belt-connected. 

The safety valve is normally situated atop the air reservoir. There must be no restriction on all blow-off points. Compressors can be hazardous to work around because they do have moving parts. Ensure that clothing is kept away from belt drives, couplings and exposed shafts. 

Expanded-metal guards on chains, couplings, belts, etc. Sheet-metal guards restrict easy inspection of lube points and moving seal parts. 

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... 

Simple apparatus may be connected directly to the shaft of a motor or a turbine. More often, there will be some form of transmission device between the driver and the load. This device may be a coupling, a gear train, a belt, or a chain. The following discussion will not cover variable-speed drives. Most of the safety considerations for the fixed-ratio devices treated below apply to all moving and rotary equipment. 

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