Particle-beam interface efficiency

The particle-beam interface is an analyte-enrichment interface in which the column effluent is pneumatically nebulized into a near atmospheric-pressure desolvation chamber connected to a momentum separator, where the high-mass analytes are preferentially directed to the MS ion source while the low-mass solvent molecules are efficiently pumped away (71, 72). With this interface, mobile phase flow rates within the range O.l-l.O ml/min can be applied (73). Since the mobile phase solvent is removed prior to introduction of the analyte molecules into the ion source, both EI and CI techniques can be used with this interface. 

In a particle-beam interface (PBI), the column effluent is nebulized, either pneumatically or by TSP nebulization, into a near atmospheric-pressure desolvation chamber, which is connected to a momentum separator, where the high molecular-mass analytes are preferentially transferred to the MS ion source, while the low molecular-mass solvent molecules are efficiently pumped away. The analyte molecules are transferred in small particles to a conventional EI/CI ion source, where they disintegrate in evaporative collisions by hitting a heated target, e.g., the ion source wall. The released molecules are ionized by El or conventional CL... 

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]. 

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. 

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