Open tubular column thick films

Restek Rtx-IMS fused-silica open-tubular column (FSOT) with integral guard column, 30 m X 0.25-mm i.d. and 0.25-p.m film thickness Eppendorf fixed-volume pipets, 0.50-mL Eppendorf fixed-volume pipefs, 1.0-mL Eppendorf pipel lips, 1.0-mL Amber-glass boftles wifti Teflon-lined caps, 4-oz... 

Figure 1.4 Variation of the resistance to mass transfer in the mobile phase, C , and stationary phase, Cj, as a function of the capacity factor for open tubular columns of different internal diameter (cm) and film thickness. A, df 1 micrometer and D, 5 x 10 cm /s B, df 5 micrometers and D, 5 x 10 cm /s and C, df - 5 Micrometers and 0, 5 x 10 cm /s.

Numerous materials have been used to fabricate open tubular columns. Most early studies were conducted using stainless steel tubing and later nickel tubing of capillary dimensions [147-149]. These materials had rough inner surfaces (leading to non-uniform stationary phase films), metal and oxide impurities at their surface which were a cause of adsorption, tailing, and/or decomposition of polar solutes and because their walls were thick, thermal Inertia that prevented the use of fast temperature programming. None of these materials are widely used today. 

There are surprisingly few studies of the retention mechanism for open tubular columns but the theory presented for packed columns should be equally applicable. For normal film thicknesses open tubular columns have a large surface area/volume ratio and the contribution of interfacial adsorption to retention should be significant for those solutes that exhibit adsorption tendencies. Interfacial adsorption has been shown to affect the reproducibility of retention for columns prepared with nonpolar phases of different film thicknesses [322-324]. The poor reproducibility of retention index values for columns prepared from polar phases was demonstrated to be c(ue to interfacial... 

Figure 8.19 Two-diaenslonal separation of the components of a coal derived gasoline fraction using live switching. Column A was 121 n open tubular column coated with poly(ethelene glycol) and column B a 64 m poly(dimethylsiloxane) thick film column. Both columns were temperature programmed independently taking advantage of the two oven configuration. Peak identification 1 acetone, 2 2-butanone, 3 > benzene, 4 isopropylmethylketone, 5 isoprop-anol, 6 ethanol, 7 toluene, 8 => propionitrile, 9 acetonitrile, 10 isobutanol, 11 — 1-propanol, and 12 = 1-butanol. (Reproduced with permission from Siemens AG).

The chromatographic column used was a wall-coated, open tubular column (WCOT) (J W Scientific) with a DB-1 Durabond chemically bonded stationary phase that had a nominal film thickness of 0.25 pm. The column was 60 m long X 0.32 mm i.d. The DB-1 stationary phase has chromatographic properties similar to SE-30. 

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.]...

Gas Chromatograph -- A Varian 6000 equipped with two constant-current/pulsed-frequency electron capture detectors, a 30-m x 0.53-mm ID DB-5 fused-silica open-tubular column (1.5-/xm film thickness), and a 30-m x 0.53-mm ID DB-1701 fused-silica open-tubular column (1.0-/im film thickness), both connected to a press-fit Y-shaped fused-silica inlet splitter (Restek Corporation, Bellefonte, Pennsylvania), was used to analyze for the nitroaromatic compounds. The columns were temperature-programmed from 120°C (1.0-min hold) to 200°C (1-min hold) at 3°C/min, then to 250°C (4-min hold) at 8°C/min injector temperature 250°C detector temperature 320°C helium carrier gas 6 mL/min nitrogen makeup gas 20 mL/min. 

A programmed temperature-vaporization (PTV) injector (with a sorbent-packed liner) was used to preconcentrate and inject the sample. Thermal desorption was performed and the analytes were passed to a primary column (16 m X 0.32 mm i.d., film thickness 5 p.m, 100% methyl polysiloxane) and separated according to analyte vapour pressure. Selected heart-cuts were transferred to a second column (15 m X 0.53 mm i.d., Al203/Na2S04 layer, open tubular column with 10 (im stationary phase) where final separation was performed according to chemical functionality. 

Open tubular columns are simply capillary tubes in which the inside of the column wall is used as the support for the liquid phase. These wall-coated open tubular columns (WCOT) have the stationary phase distributed in the form of a thin film on the inside surface of the open capillary tube, the walls thus serving as the support. In order to reduce the thickness of the liquid phase film, a porous layer may be formed on the inside wall of the capillary tubing and then coated with the liquid phase to produce a support-coated open tubular column (SCOT). Porous-layer open tubular colunms (PLOT) are similar to SCOT colunms, the difference being that in the former, the stationary phase is deposited on fine crystalline particles or glass powder which is adsorbed onto the walls of the tube. In both cases, the available surface area of the wall is increased, and allows an increased amount of liquid phase to be accommodated in the same length and diameter of tubing. The whisker-walled (WW) colunm consists of whiskers chemically etched on the surface of the wall, which also result in a significant increase in the available surface area. Wall-coated, porous-layer, and support-coated capillary columns are all available as whisker-walled, i.e., WWCOT, WWPLOT, and WWSCOT, respectively. 

The pioneering gas-liquid chromatographic studies in the early 1950s were carried out on packed columns in which the stationary phase was a thin film of liquid retained by adsorption on the surface of a finely divided, inert solid support. From theoretical studies made during this early period, it became apparent that unpacked columns having inside diameters of a few tenths of a millimeter could provide separations that were superior to those of packed columns in both speed and column efficiency. In such capillary columns, the stationary phase was a film of liquid a few tenths of a micrometer thick that uniformly coated the interior of capillary tubing. In the late 1950s, such open tubular columns were constructed the predicted... 

It is interesting that while hm n is smaller for low-k solutes in open tubular columns of conventional film thickness, in these very thick film columns the reverse is true h, is now smaller for high-k solutes (Figure 6). 

Figure 2.1. Van Deemter plots indicating the influence of the choice of carrier gas on column efficiency for thin-film (A) and thick-film (B) open tubular columns for solutes with different retention factors.

Figure 7.6. Affect of column internal diameter and stationary phase film thickness on efficiency for open tubular columns operated at 10 Uopi with low-density supercritical fluid carbon dioxide as the mobile phase. (From ref. f 100 and 101] Wiley-VCH)...

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