Stream-splitter

A stream-splitter may be used at the end of the column to allow the simultaneous detection of eluted components by destructive GC detectors such as an FID. An alternative approach is to monitor the total ion current (TIC) in the mass spectrometer which will vary in the same manner as the response of an FID. The total ion current is the sum of the currents generated by all the fragment ions of a particular compound and is proportional to the instantaneous concentration of that compound in the ionizing chamber of the mass spectrometer. By monitoring the ion current for a selected mass fragment (m/z) value characteristic of a particular compound or group of compounds, detection can be made very selective and often specific. Selected ion monitoring (SIM) is more sensitive than TIC and is therefore particularly useful in trace analysis. 

These have now been superseded by capillary columns, which offer greatly improved separation efficiency. Fused silica capillary tubes are used which have internal diameters ranging from 0.1 mm (small bore) to 0.53 mm (large bore) with typical lengths in excess of 20 m. The wall-coated open tubular (WCOT) columns have the internal surface of the tube coated with the liquid (stationary) phase and no particulate supporting medium is required. An alternative form of column is the porous-layer open tubular (PLOT) column, which has an internal coating of an adsorbent such as alumina (aluminium oxide) and various coatings. Microlitre sample volumes are used with these capillary columns and the injection port usually incorporates a stream splitter. 

A stream-splitter attached to the exit tube of a thermal conductivity detector can be used to identify the functional groups of gas chromatographic effluents. Table 4.1 lists functional group tests and limits of detection. A review of elemental analysis by GC is given by Rezl and Janak (9). 

An HPLC chromatograph was used together with a mass detector (when required, a stream splitter (app. 10 1) was inserted between the column and the detector). A column (250 X 4.6-mm ID) of NUCLEOSIL 5SA was flushed with 1% aqueous ammonium nitrate solution at a flow rate of 0.5 ml/min for 1 h, then with distilled water at 1 ml/min for 1 h. Silver nitrate (0.2 g) in water (1 ml) was injected onto the column in 50-/zl aliquots at 1-min intervals silver began to elute from the column after about 10 min. Twenty minutes after the last injection, the column was washed with methanol for 1 h, then with 1,2-dichloroethane-dichloromethane (1 1) for another hour. The three solvent reservoirs contained the following (A) 1,2-dichloroethane-dichloromethane (1 1) (B) acetone and (C) acetone-acetonitrile (9 1). For linoleic acid-rich seed oils, gradients of A were employed to 50% A-50% B over 15 min, then to 50% B-50% C over a further 25 min and held there for 5 min. For linolenic acid-rich seed oils, C was changed to acetone-acetonitrile (4 1), and the flow rate was increased to 1 ml/min gradients of A were utilized to 50% A-50% B over 10 min, then to 70% B-30% C over 20 more min, and finally to 100% C over another 30 min. 

Preparative separations in the grams per injection level are different. Separations are run isocratic in 1- to 3-in columns with large pore, fully porous packings (35-60jUm). An analytical, two-pump system can just barely reach the 20-mL/min flow rates needed to run a 1-in column. Special preparative HPLC systems deliver flow rates of 50-500 mL/min to handle the larger bore columns. A stream splitter is used to send part of the flow through a refractive index detector with a flow cell designed for concentrated solutions. 

However, the most economical and octane effective route to reduce benzene is to eliminate benzene and benzene precursors from the naphtha reformer feed by pre-fractionation in an up-stream splitter and then send these precursors to an isomerization unit. With this approach, benzene will be saturated and isomerised to a mixture of higher octane saturated cyclics. Depending on the feed benzene content, various solutions can be applied to handle the heat load from the saturation of benzene. These heat management solutions entail saturation of the benzene in the iso-... 

SPLITT-FFF uses stream splitters at the channel inlet and outlet which enables the separation of a mixture into two fractions. Although the separation of the sample is also achieved by the action of an external field, the mechanism of separation is different from FFF. The separation in FFF is along the flow axis of the channel because of the different flow velocities of each component, whereas in SPLITT separation is over the thinnest dimension of the channel. While conventional FFF is an analytical tool requiring operation with very small samples, SPLITT is a preparative tool which can be operated with continuous sample feed [336,337]. SPLITT channels are similar to FFF channels but with two carrier inlet streams a and b and two outflow streams a and b as illustrated in Fig. 26. 

Very fast hydrodynamic relaxation as can be achieved by stream splitters or frit inlets (see Fig. 12) so that there is no need for a stop-flow or focusing period. It is important that the injection time can serve as a triggering pulse for an automated fractionator coupled to the FFF outlet. 

Sample concentration after the sample fractionation as can be achieved by stream splitters or frit outlets. 

Ozone Competition Reaction Procedures. In the relative rate studies, the solvent-saturated ozone—oxygen stream was passed into a glass bubbler reactor vessel charged with 4 ml of about 4 X 10"2M concentration of each of the two silanes to be competitively ozonized as well as of an inert saturated aliphatic hydrocarbon to function as internal standard. (For example, n-undecane was used for the tributylsilane/trihexylsilane study.) The effluent from the reactor passed through a solvent-filled bubble counter to visualize the flow. The inlet stream splitter mentioned earlier was adjusted to allow 2—4 hours for each runs completion, as determined by experience. The temperature was controlled at 0°C in both the saturator and the reactor by ah ice bath. 

T. Raglione and R. Hartwick, Liquid chromatography-gas chromatography using microbore high-performance liquid chromatography with bundled capillary stream splitter, Anal. Chem., 55 2680-2683 (1986). 

In computer-based methods for solving the MESH equations, it is common to replace the energy balance of the condenser (with or without the associated stream splitter) and reboiler with a specification equation. Possible specifications include... 

---