Capillary columns inner diameter

Although new types of columns will undoubtedly continue to be introduced, at present much research is being performed for the purpose of improving the existing ones. For packed columns the primary goal is the reduction in the number of active sites, while for capillaries it is the reproducible and uniform coating of capillaries with inner diameters closer to the theoretical optimum for mass transfer, the latter will unfortunately require further improvements in sample introduction and detection before the predicted improvements in resolution can be fully realized. 

Modem GC uses capillary columns (internal diameter 0.1-0.5 mm) up to 60 m in length. The stationary phase is generally a cross-linked silicone polymer, coated as a thin film on the inner wall of the fused silica (Si02) capillary at normal operating temperatures, this behaves in a similar manner to a liquid film, but is far more robust. Common stationary phases for GC are shown in Fig. 32.4. The mobile phase ( carrier gas ) is usually nitrogen or helium. Selective separation is achieved as a result of the differential partitioning of individual compounds between the carrier gas and silicone polymer phases. The separation of most organic molecules is influenced by... 

A compact sensor of greatly reduced dimensions (outer diameter x length 36 x 46 mm) has been constructed and is shown in Fig. 2. In order to conveniently accommodate enzyme columns and to ensure isolation from ambient temperature fluctuations, a cylindrical copper heat sink was included. An outer Delrin jacket further improved the insulation. The enzyme column (inner diameter x length 3x4 mm), constructed of Delrin, was held tightly against the inner terminals of the copper core. Short pieces of well-insulated gold capillaries (outer diameter/inner diameter 0.3/0.2 mm) were placed next to the enzyme column as temperature-sensitive elements. Microbead thermistors were mounted on the capillaries with a heat-conducting epoxy. Two types of mini system has been constructed as discussed below. 

Typical capillary column GC curves can be similarly generated, as shown In Figure 1c. In this case an Intermediate value for the binary diffusivity, 0.2 cm /s, was used along with two column Inner diameters, 250 pm and 50 pm. The 50 pm diameter Is unusually small for ultrahlgh resolution capillary GC work while the 250 pm diameter Is in the middle of the diameter range commonly used in this area. As seen in Figure 1c, a comparison of the 50 pm diameter SFC curve to the 50 pm GC curve (Curves 3 and... 

In an open tubular column, h= H/dc, where d is the column inner diameter. In capillary GC, reduced plate heights of less than 1 can be obtained. 

The following GC-MS analysis is commonly done using a 12-16 minute HP5MS capillary GC column (inner diameter 0.2 mm, film thickness 0.33 pm) with helium as carrier gas operated at constant pressure (approximately 12psi) with 0.8-1.0mL/min. The temperature gradient of the GC usually starts from 100°C to 300°C with 15°C/min. The... 

In capillary electrophoresis the conducting buffer is retained within a capillary tube whose inner diameter is typically 25-75 pm. Samples are injected into one end of the capillary tube. As the sample migrates through the capillary, its components separate and elute from the column at different times. The resulting electrophero-gram looks similar to the chromatograms obtained in GG or HPLG and provides... 

Capillary Tubes Figure 12.42 shows a cross section of a typical capillary tube. Most capillary tubes are made from fused silica coated with a 20-35-)J,m layer of poly-imide to give it mechanical strength. The inner diameter is typically 25-75 )J,m, which is smaller than that for a capillary GC column, with an outer diameter of 200-375 )J,m. 

The catalytic reforming of CH4 by CO2 was carried out in a conventional fixed bed reactor system. Flow rates of reactants were controlled by mass flow controllers [Bronkhorst HI-TEC Co.]. The reactor, with an inner diameter of 0.007 m, was heated in an electric furnace. The reaction temperatoe was controlled by a PID temperature controller and was monitored by a separated thermocouple placed in the catalyst bed. The effluent gases were analyzed by an online GC [Hewlett Packard Co., HP-6890 Series II] equipped with a thermal conductivity detector (TCD) and carbosphere column (0.0032 m O.D. and 2.5 m length, 80/100 meshes), and identified by a GC/MS [Hewlett Packard Co., 5890/5971] equipped with an HP-1 capillary column (0.0002 m O.D. and 50 m length). 

Motokawa, M., Ohira, M., Minakuchi, H., Nakanishi, K., Tanaka, N. (2007). Performance of octadecylsilylated monolithic silica capillary columns with 530 pm inner diameter in high performance liquid chromatography. J. Sep. Sci., 29, 2471-2477. 

Figure 5.19 Formation of amino acids on ice surfaces irradiated in the laboratory (Nature Nature 416, 403-406 (28 March 2002) doi 10.1038/416403a-permission granted). Data were obtained from analysis of the room temperature residue of photoprocessed interstellar medium ice analogue taken after 6 M HCl hydrolysis and derivatization (ECEE derivatives, Varian-Chrompack Chirasil-L-Val capillary column 12 m x 0.25 mm inner diameter, layer thickness 0.12 pirn splitless injection, 1.5 ml min-1 constant flow of He carrier gas oven temperature programmed for 3 min at 70°C, 5°C min-1, and 17.5 min at 180°C detection of total ion current with GC-MSD system Agilent 6890/5973). The inset shows the determination of alanine enantiomers in the above sample (Chirasil-L-Val 25 m, single ion monitoring for Ala-ECEE base peak at 116 a.m.u.). DAP, diaminopentanoic acid DAH, diaminohexanoic acid a.m.u., atomic mass units.

FIGURE 14.3 Fast analysis of control drugs and metabolites using a 15 cm x 300 fim inner diameter capillary column packed with 3 /tin C18 particles (Micro-Tech Scientific MC-15-C18SS-320-EU) operated at 10 /tL/min gradient flow rate. UV at 278 nm. (Source Drug Enforcement Administration, Southwest Laboratory, Vista, California and S. DiPari.)... 

FIGURE 14.4 Chromatograms of high speed isocratic capillary LC elution of three components. Column 15 cm x 320 /im inner diameter, 5 /im C18 particles. Column head pressure 6800 psi at 48 /(L/min flow rate. System XTS two-dimensional splitless ultrahigh pressure nano UHPLC, Micro-Tech Scientific, Vista, California. 

Ee was determined by gas chromatography (GC) on a Supelco Beta-DEX 120 column (fused-sihca capillary column, 30 m, 0.25 mm inner diameter, 0.25 mm film thickness Supelco, Buchs, Switzerland) with spht injection (20 1) and an isothermal oven temperature profile at 90 °C for separation of styrene oxide enantiomers. 

An open-tubular column is a capillary bonded with a wall-supported stationary phase that can be a coated polymer, bonded molecular monolayer, or a synthesized porous layer network. The inner diameters of open-tubular CEC columns should be less than 25 pm that is less than the inner diameters of packed columns. The surface area of fused silica tubing is much less than that of porous packing materials. As a result, the phase ratio and, hence, the sample capacity for open-tubular columns are much less than those for packed columns. The small sample capacity makes it difficult to detect trace analytes. 

Compared to packed columns, open-tubular columns have no bubble formation problems because end-frits are not needed, small internal diameter columns are used, and the stationary phase is homogeneous. The column length can also be easily shortened. Excellent mass sensitivity can be achieved by using capillaries with smaller inner diameters. The EOF in an open-tubular column is higher than that in a packed column because a greater... 

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