Particle-beam interface advantages

The particle-beam interface provides El spectra from HPLC eluates and this is of great advantage over other interfaces which provide only molecular weight information. Why then, is it of advantage to be able to generate Cl spectra from the particle-beam interface ... 

MS is becoming the detection system of choice for LC by virtue of its flexibility and high selectivity for individual solutesHowever, LC-MS is always less sensitive than GC-MS as a result of the need to transfer the analytes from the liquid phase into a high-vacuum gas phase. Other limitations of LC-MS combination include the inability to use nonvolatile buffers, the narrow optimum range for eluent flow rate influence of the proportion of organic modifier on the sensitivity, and the narrow choice of ionization methods.Nevertheless, LC-MS has been widely accepted as an advantageous choice for the determination of carbamate pesticides in water matrices, which is more robust and flexible in the absence of derivatization. Thermospray and particle-beam interfaces are probably most commonly used for offline and online determination of carbamates in Atmospheric pressure sources such as... 

The particle beam interface (Fig. 6) was created under the acronym MAGIC (monodisperse aerosol generator interface for chromatography) [28]. Now, the aerosol is produced by a variety of means (with auxiliary gas, thermospray, or ultrasonic nebulizers) at atmospheric pressure and a uniform distribution of the droplets results in particles of a narrow size distribution, which can be handled more efficiently by the separator. The droplets are dried to particles in a heated expansion chamber, and a momentum separator isolates the particles from the gas. In the source, the particles are destroyed by impact and the sample is released and ionized by using El, Cl, or even FAB. The appearance of the El spectra is almost identical to conventional El spectra obtained by direct probe or GC/MS. Therefore, library searches are possible, which is the major advantage of this interface. 

The obvious alternative for the in-line flow-through cell in HPLC-FTIR is mobile-phase elimination ( transport interfacing), first reported in 1977 [495], and now the usual way of carrying out LC-FTIR, in particular for the identification of (minor) constituents of complex mixtures. Various spray-type LC-FTIR interfaces have been developed, namely, thermospray (TSP) [496], particle-beam (PB) [497,498], electrospray (ESP) [499] and pneumatic nebulisers [486], as compared by Som-sen et al. [500]. The main advantage of the TSP-based... 

For the HPLC-MS systems, many different ionization techniques have been described in the past. Various interface, ionization methods, and operating techniques applicable to LC-MS are discussed in [117J for instance Thermospray, particle beam, electrospray (ES), field desorption (FD), fast atom bombardment (FAB), time of flight (TOF), etc. The electrospray technique produces a soft ionization for thermally labile compounds, while FAB has the advantage that higher molecular mass samples can be introduced into the mass spectrometer. Table 8 offers a rough guide to the applicability of various LC-MS interfaces. For more detailed information on LC-MS, see [118]. 

In principle, there is no upper bound in measurements of particle velocity (or stress) using laser velocity interferometry. In practice, very high-pressure shock fronts can cause copious jetting of microparticles from the free surface (Asay et al., 1976), obscuring the surface from the laser beam. To alleviate this, optically transparent materials can be bonded to the specimen, and particle velocity measurements are then made at the specimen/window interface. This has the added advantage of simulating in situ particle velocity... 

The interferometer has several advantages over dark field scattering instruments. Because it is a bright field instrument it is less sensitive to the stray light scattered by interfaces between the instrument s capillaiy cell wall and the liquid medium. The instrument can also identify signals created by bubbles thus avoiding false counts. It can also measure flow-rate and it is more sensitive to particles with a refractive index near that of the liquid than dark field instruments because it can look at forward light without noise interference from the incident laser beam. 

The use of optical methods which probe interface electronic and vibrational resonances offers significant advantages over conventional surface spectroscopic methods in which, e.g. beams of charged particles are used as a probe, or charged particles emitted from the surface/interface after photon absorption are detected. Recently, three-wave mixing techniques such as second-harmonic generation (SHG) have become important tools to study reaction processes at interfaces. SHG is potentially surface-sensitive at nondestructive power densities, and its application is not restricted to ultrahigh vacuum (UHV) conditions.However, SHG suffers from a serious drawback, namely from its lack of molecular selectivity. As a consequence, SHG cannot be used for the identification of unknown surface-species. 

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