Open tubular column split

Injection into open tubular columns split routine for introducing small sample volume into open tubular column splitless best for trace levels of high-boiling solutes in low-boiling solvents on-column best for thermally unstable solutes and high-boiling solvents best for quantitative analysis... 

Figure 6.11 Schenatic diagran of a split/splitless valve injector (A) and a timed-split injector (B) for open tubular column SFC.

Figure 24-14 Injection port for split injection into an open tubular column.

Figure 24-16 Split and splitless injections of a solution containing 1 vol% methyl isobutyl ketone (b.p. 118°C) and 1 vol% p-xylene (b.p. 138°C) in dichloromethane (b.p. 40°C) on a BP-10 moderately polar cyanopropyl phenyl methyl silicone open tubular column (0.22 mm diameter x 10 m long, film thickness = 0.25 m, column temperature = 75°C). Vertical scale is the same for A-C. In D, signal heights should be multiplied by 2.33 to be on the same scale as A-C. [From R J. Marriott and P. D. Carpenter, Copillory Gas Chromatography Injection," J. Chem. Ed. 1996, 73, 96.]...

The most general purpose detector for open tubular chromatography is a mass spectrometer. Flame ionization is probably the most popular detector, but it mainly responds to hydrocarbons and Table 24-5 shows that it is not as sensitive as electron capture, nitrogen-phosphorus, or chemiluminescence detectors. The flame ionization detector requires the sample to contain SlO ppm of each analyte for split injection. The thermal conductivity detector responds to all classes of compounds, but it is not sensitive enough for high-resolution, narrow-bore, open tubular columns. 

The split/splitless detector has been designed for use with open-tubular columns or solid-coated open-tubular (SCOT) columns. Due to the small dimensions of such columns, they have very limited sample load capacity and, thus, for their effective use, require sample sizes that are practically impossible to inject directly. The split injector allows a relatively large sample (a sample size that is practical to inject with modern injection syringes) to be volatilized, and by means of a split-flow arrangement, a proportion of the sample is passed to the column while the remainder is passed to waste. A diagram of a split/splitless injector is shown in Fig. 1. 

Where the C-term is split into two parts — one for the resistance in the Uquid phase (Ciu) and the another one for the resistance to mass transfer in the gas phase (Cgu). Hawkes [22] suggested that the Cg term was an indefinite combination of several factors, including particle size, column diameter and the diffusion coefficient of the analyte in the carrier gas. The most important parameter in Hawkes equation is the column diameter, dc. For both packed and open tubular columns, the analyte zone broadening is a function of the square of the diameter. For further details, please consult the paper by Hawkes. 

The benzene fraction was initially examined by GLC using 100 ft. support coated open tubular columns containing Carbowax 1540 polyethylene glycol) and squalane (Figure 3) as the liquid phases. Quantitative data were obtained at 45 °C. on the squalane column with a helium flow of 3.0 ml./min. The Perkin Elmer Model 880 gas-liquid chromatograph, equipped with a stream splitting device and hydrogen flame... 

Figure 3.5. Schematic diagram of a hot split/splitless injector for open tubular columns, (From ref. [50] Perkin-Elmer Co.).

Figure 3 A hot split/splitless injector for open tubular column gas chromatography. (From Tipler A and Ettre LS (1997) The Prevent System and its Application in Open-Tubular Column Gas Chromatography. Norwalk Perkin-Elmer Corporation.)...

Figure 22-7 Injection port operation for (q) split, (b) splitless, and (c) on-column injection into an open tubular column. A slow flow of gas past the inside surface of the septum out to waste cools the rubber and prevents volatile emissions from the rubber from entering the chromatography column.

In the dynamic split mode, which is the most frequently applied technique in open tubular column SFC, the split ratio is determined by the ratio of the flow out of the column to the flow out of the split restrictor. Thus, if the flow out of the split is 500 times faster than the flow out of the column, the split ratio is 1 500. The disadvantage of the dynamic split technique is that obtaining reproducible results can be difficult with certain samples. 

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