Capillary column installation

The column is swept continuously by a carrier gas such as helium, hydrogen, nitrogen or argon. The sample is injected into the head of the column where it is vaporized and picked up by the carrier gas. In packed columns, the injected volume is on the order of a microliter, whereas in a capillary column a flow divider (split) is installed at the head of the column and only a tiny fraction of the volume injected, about one per cent, is carried into the column. The different components migrate through the length of the column by a continuous succession of equilibria between the stationary and mobile phases. The components are held up by their attraction for the stationary phase and their vaporization temperatures. 

Hydrolytic Kinetic Resolution (HKR) of epichlorohydrin. The HKR reaction was performed by the standard procedure as reported by us earlier (17, 22). After the completion of the HKR reaction, all of the reaction products were removed by evacuation (epoxide was removed at room temperature ( 300 K) and diol was removed at a temperature of 323-329 K). The recovered catalyst was then recycled up to three times in the HKR reaction. For flow experiments, a mixture of racemic epichlorohydrin (600 mmol), water (0.7 eq., 7.56 ml) and chlorobenzene (7.2 ml) in isopropyl alcohol (600 mmol) as the co-solvent was pumped across a 12 cm long stainless steel fixed bed reactor containing SBA-15 Co-OAc salen catalyst (B) bed ( 297 mg) via syringe pump at a flow rate of 35 p,l/min. Approximately 10 cm of the reactor inlet was filled with glass beads and a 2 pm stainless steel frit was installed at the outlet of the reactor. Reaction products were analyzed by gas chromatography using ChiralDex GTA capillary column and an FID detector. 

One of the major practical problems to the installation of HPLC as a permanent process monitor is the need to replace solvent. A large solvent reservoir may present problems both in terms of size and safety. One solution is the use of packed capillary columns, which consume much less solvent than conventional columns, as the comparison (at constant linear velocity) in Table 1 shows. 

Column. The capillary column must be correctly installed into the inlet, a procedure that is inlet and instrument dependant. In general, the column end is placed a specified distance into the inlet, beyond a fitting at the bottom end of the inlet. Each instrument vendor provides specific instructions on column installation that should be followed carefully. It is especially important to ensure that the seal between the inlet and column is leak-free and not contaminated. 

The derivatized samples were analyzed on a Hewlett-Packard 5890 series IIGC (helium carrier gas) coupled to a Hewlett-Packard 5971 mass-selective detector (MSD). A 60 m, 0.32 mm i d., 0.25-im film, SE-30 fused silica capillary column (J W Scientific, Folsom, CA) was installed in the GC, and an on-column injector (SGE model OCl-3) held at ambient temperature was fitted to the colunrn inlet. Samples (0.5 p,L) were injected directly into the column held at 105°C... 

Capillary Gas Chromatography (HRGC). Analytical separations were performed on a Varian 3700 GC instrument as well as on a Carlo Erba type 5360 Mega Series gas chromatograph. The Varian 3700 GC system was modified with a hot split/splitless injector and additionally equipped with a commercially available inlet splitter (Gerstel, Mulheim/Ruhr) in order to install two capillary columns... 

Because of all these reasons, so-called wide-bore capillaries (dc 500 pm) have recently gained considerable popularity. These columns, which are usually provided with a thick (about 1 pm) film of stationary phase, behave in a fairly similar way to packed columns. They show low pressure drops (allowing them to provide a much higher efficiency than packed columns), may easily be installed in most instruments and have a high sample capacity. However, they also behave similar to packed columns in terms of separation speed. Therefore, the current capillary columns with diameters between 100 and 300 pm form a reasonable compromise between instrumental limitations and theoretical promises. 

Installation of Capillary Columns Glass columns, whidi are coiled when purdiased, must have straight ends to allow than to fit into imions at the injector and detector. A device is commercially available to straightoi capillary ends, but it is more usual to use a small butane flame. The column is suspended on a clamp stand and a supply of csilicone rubber tubing to produce a flow of about 0.5 ml/ min. A cool, small butane flame is used to apply... 

At optimized operating conditions, uncoated and deactivated restriction capillaries are installed between injector and precolumn by means of simple press-fit connectors to reduce carrier gas velocity within the precolumn. By means of such a column combination suitable pre- and main columns may be easily exchanged and adopted to optimal efficiency [28]. 

Figure 2.17 Three detectors connected in series. At the outlet of a capillary column, either in series or in parallel and depending upon whether any of them destroy the sample, several detectors can be installed. Here, three chromatograms of an injected mixture are obtained from each detector. Note that the sensitivity varies significantly from one detector to another.

Fused silica is the most common inert and temperature stable material used in the manufacture of capillary columns. They are flexible, robust and easy to install. Many laboratories find difficulty in separating the ever increasing list of volatile compounds requiring analysis. Many phases suffer from low thermal stability, and analysis times are unacceptably long. The most common column used in the analysis of VOCs is the 624 column, available from several suppliers worldwide. 

Figure 4. Glass capillary gas chromatograms of aromatic hydrocarbons in New York Bight surface sediments. Analysis conditions 20 m X 0.32-mm i.d. Jaeggi SE-54 column installed in a Carlo Erba Model 2150 gas chromatograph equipped with split/splitless injection helium carrier gas at 0.55 kg/cm2 injection at room temperature, program 80°-240°C at 3°/minute injector and detector at 250°C. Numbered peaks are identified in Table V.

For many years GC made use of TCDs almost exclusively, but with the advent of capillary columns, which are limited to smaller samples, greater sensitivity was required. One method of detection that can give greater sensitivity is a modification of the ionization chamber long used for radiation detection. The effluent from the chromatographic column is allowed to flow through such a chamber, where it is subjected to a constant flux of beta-ray electrons from a permanently installed radioisotope. 

When a capillary column is installed in an instrument it should be checked for carrier gas flow before connecting the detector end of the column to avoid the possibility of heating a column with no flow. 

Install the capillary column in the GC injector and condition the column according to the manufacturer s specifications. 

The second major advantage is their flexibility, cind especially the ease of column installation. Fused-silica capillary columns have virtually replaced gletss columns for this reason. 

The price of a column ( 200- 800) may be viewed as relatively small compared to the initial, the routine, and preventive-maintenance costs of the instrument. In fact, a laboratory may find that the cost of a set of air and hydrogen gas cylinders of research grade purity for FID operation is far greater than the price of a single conventional capillary column Consequently, the column should be carefully selected for an application, handled with care following the suggestions of its manufacturer, and installed as recommended in the user s instrument manual to derive maximum performance from a gas chromatographic system. 

It is important to select the proper ferrule inner diameter (i.d.) to be compatible with the outer diameter (o.d.) of the capillary column, or a carrier-gas leak will result after installation. Ferrules having an i.d. of 0.4 mm are recommended for 0.25-mm-i.d. columns, 0.5-mm-i.d. ferrules are recommended for... 

Outlined below are guidelines for the preparation of a capillary column for installation. 

FIGURE 3.56 Illustration of the quick-connect fitting for installation of capillary columns (a) internal sealing mechanism and (b) sealing mechanism inserted into fitting and locked into place (photographs courtesy of the Quadrex Corp.)... 

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