Split ratio

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

Split Injection2 In the split injector, the injected sample is vaporized into the stream of carrier gas, and a portion of the sample and solvent, if any, is directed onto the head of the GC column. The remainder of the sample is vented. Typical split ratios range from 10 1 to 100 1 and can be calculated from the equation ... 

Recommended injection volume with a split injection is 1-2 ft 1. If a large sample has to be injected, inject it slowly as previously mentioned. Typical split ratios are 1 10 to 1 100. (Use a packed liner or other suitable liner.)... 

The use of a fused silica capillary column for the GC analysis of the neutral oil extract has provided the means for improving the resolution of components in a more inert system. The sultones are determined by temperature-programmed GC over CP-Sil-5 CB (methyl silicone fluid) in a 25 m x 0.2 mm fused silica capillary column using nonadecane as internal standard. A sample split ratio of 1 100 is recommended for a 3-pl injection. 

Reaction conditions 0.1 g of the zeolite Y modified catalyst, tested in a conventional glass microreactor with racemic butan-2-ol (7.35 x 10" mol h-1), prevaporized in a nitrogen diluent (6.2 -6.7 x 10" mol h-1). Products were analyzed using on-line GC with a 40m capillary y- cyclodextrin colimm with trifluoroacetyl stationary phase, temperature programmed from 25-70 "C with a split ratio of 120 1. 

Column Solvent A Solvent B Injection volume Flow rate Split ratio... 

Split/splifless (approximately 1 1 split ratio), 270 °C Splifless, purge on at 0.6 min... 

Inject the test mixture under conditions that allow ca. 2 ng of a single test substance to enter the column (e.g., 1 microliter with a split ratio of 1 20 to 1 50, depending on injector design). 

Unfortunately, the preset split flow ratio is only an approximate indication of the sample split ratio. The latter depends in a complex way on many parameters, including the range of sample volatilities, sample solvent, volume of sample injected. 

An alternative form of split injection is the timed split technique, Figure 6.11 [130,131,133]. In this case the column is connected directly to the valve and the valve actuator is controlled electronically to turn the valve to the inject position and back very rapidly with only a portion of the sample in the loop displaced to the column. Timed split allows variable volumes to be injected by changing the valve actuator tine and provides more reproducible splitting than the dynamic split technique. However, it suffers from many of the same problems as dynamic split, namely, poor accuracy, split ratios that depend on pressure, and high detection limits. 

Instrumentation allowing high inlet pressure (4-10 bar) and high split ratios (1 1000). 

Hot split Sample (usually liquid) passes from syringe into hot inlet rapid vaporisation initial oven temperature not critical small fraction allowed to column (split ratios 1 20 to 1 400) Concentrated samples Narrow 0.1-2 0.01-10... 

Layout of several tested prototype HPLC hypemations. Splitting ratios are indicated... 

The loop for the 2nd-D was loaded with the effluent of the 1 st-D at 50 pL/min for 1 min 58 s, and then the injection valve was turned to inject the 100 pL fraction for 2 s onto the 2nd-D HPLC. The flow rate was 5 mL/min, and the valve was turned back for the next loading, resulting in fractionation of the lst-D every 2 min. In this case less than 2% of the effluent from the 1 st-D was wasted during sample injection. The 2nd-D effluent eluted at 5 mL/min from the 2nd-D column, passed through a UV detector, and then was split by using a T-joint at approximately a 1/140 split ratio, resulting in a flow rate of ca. 36 pL/min going into the spray capillary for ESI-TOF-MS detection. 

The above devices are flow intrusive, subjected to wear and the splitter itself cannot control changing downstream conditions. A potentially more direct and efficient approach is to monitor the change in flow conditions downstream of a splitter (Barnes and Mumane, 1995) and employ active splitters (Selves et al., 1995) to control the split ratio of air and hence, material. Some of the active splitters being investigated and developed by Selves et al., 1995 include ... 

Modified riffle box, as shown in Fig. 26, which uses air injection to control the split ratio. 

Figure 27. Control of split ratio using induced swirl and a Y splitter. (Selves et al., 1995.)...

Selves, T. P., Barnes, R. N., and Reed, A. R., The Use of Flow Diverting Air Injection to Actively Control the Split Ratio of Pneumatically Conveyed Particulate Materials, 5th Int. Conf. on Bulk Materials Storage, Handling and Transportation, IEAust. Proc, 1 263-271, Newcastle (1995)... 

Imperfect technology also leads to complications the splitting ratio of the Y-junctions will not be exactly equal to 1 1 and he channel structures of both... 

All of the injections were 1 microliter and the capillary column split ratio was nominally set at 200 1. Column and program times and temperatures were varied depending on the volatile products being analyzed. 

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