Jet separation

Jet separator. An interface in which carrier gas is preferentially removed by diffusion out of a gas jet flowing from a nozzle. Jet separator, jet-orifice separator, jet enricher, and jet orifice are synonymous terms. 

Separator GC/MS interface. An interface in which the effluent from the gas chromatograph is enriched in the ratio of sample to carrier gas. Separator, molecular separator, and enricher are synonymous terms. A separator should generally be defined as an effusion separator, a jet separator, or a membrane separator. 

When the temperature of an air jet attached to the ceiling is lower than the temperature of the ambient air, the jet will remain attached to the ceiling until the downward buoyant force becomes greater than the upward static pressure (Coanda force). At this point, the jet separates from the ceiling and... 

FIGURE 7.42 Maximum jet separation from ceiling b = width of two-dimensional slot, b - beam height, Xj = jet core zone length. Reproduced from Holmes and Sachariewicz. ... 

GC/MS Hewlett Packard HP5890 connected to HP5971 mass detector with a jet separator... 

Jet Separator The jet separator contains two capillary tubes that are aligned with a small space (ca. 1 mm) between them. A vacuum is created between the tubes by using a rotary pump. The GC effluent passes through one capillary tube into the vacuum region. Those molecules that continue in the same direction will enter the second capillary tube and will be directed to the ion source. Enrichment occurs because the less massive carrier gas (He) atoms are more easily collisionally diverted from the linear path than the more massive analyte molecules. 

I Most of the GC conditions given in this book are for 0.25-mm ID columns, but 0.32- or 0.53-mm ID columns also can be used. The wide bore fused silica columns are found to be more inert, probably because of the greater film thicknesses. A splitter arrangement with a jet separator is used with 0.53-mm ID columns. This arrangement shown in Figure 11.1 has the advantage of simultaneous flame ionization quantitation. 

There are two notable features of the quantitative performance of this type of interface. It has been found that non-linear responses are often obtained at low analyte concentrations. This has been attributed to the formation of smaller particles than at higher concentrations and their more easy removal by the jet separator. Signal enhancement has been observed due to the presence of (a) coeluting compounds (including any isotopically labelled internal standard that may be used), and (b) mobile-phase additives such as ammonium acetate. It has been suggested that ion-molecule aggregates are formed and these cause larger particles to be produced in the desolvation chamber. Such particles are transferred to the mass spectrometer more efficiently. It was found, however, that the particle size distribution after addition of ammonium acetate, when enhancement was observed, was little different to that in the absence of ammonium acetate when no enhancement was observed. 

Figure 9.2 Common interfaces for 6C/MS. Effusion separator (A), jet separator (B) and a membrane separator (C).

Fig. 11.15. Gas chromatography interfaces (jet separator, top membrane separator, bottom). In the jet separator, momentum of the heavier analyte molecules causes them to be sampled preferentially by the sampling orifice with respect to the helium carrier gas molecules (which diffuse away at a much higher rate). In the membrane separator, the analyte molecules are more soluble in the silicone membrane material leading to preferential permeability. Helium does not permeate the membrane with the same efficiency and is vented away.

The particle beam system is a simple transport device, very similar to a two-stage jet separator. The solvent vapour is pumped away, while the analyte particles are concentrated in a beam and allowed to enter the mass spectrometric source. Here they are vapourized and ionized by electron impact. 

A gas chromatograph (GC) can be used for the chromatographic separation of volatile analytes in complex mixtures prior to mass spectrometric analysis. This becomes especially advantageous if the GC elutes directly ( online ) into the ion source of a mass spectrometer, so-called GC-MS coupling. [63-65] Packed GC columns with a high flow can be connected via a jet-separator, but these are almost out of use at present. [66] Capillary columns provide flow rates in the order of a few milliliters per minute, therefore their back end can be connected directly at the entrance of the ion volume. 

In early GC-MS with paeked GC columns eluting several tens of milliliters per minute most of the flow had to be separated before entering the ion source to prevent the vacuum system from breakdown. [4,29,34] This was either effected by a simple split to divide the effluent in front of the inlet system by a faetor of about 1 100 or by means of a more elaborate separator, the jet separator being the best... 

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