Column tube material

The suitability of a column for a particular use depends on various factors, such as stationary phase, solid support, column tubing material, inside diameter, percent liquid loading, and temperature. Columns may be prepared in various lengths and diameters depending on the particular objective. Preparative columns may range from 0.95 to 10 cm (3/8-4 ) in diameter or larger for the collection of quantities of individual... 

Before discussing the suitability of the different column tubes that are available, it is worthwhile summarizing the packing procedures that have been applied as these usually restrict the choice of the column tube material in practice. Mainly two packing procedures have been applied up to now ... 

Dry packing involving tapping can be applied with all column tube materials. 

Apart from the restriction in the selection of the packing procedure, other demands such as resistance to chemical action by the eluent or inertness of the surface might play a decisive role in the selection of the column tube. Up to now, glass, metal and to a lesser extent polymeric materials have been tested as column tube materials. 

A major requirement for column tubes in HPLC is constancy of the column diameter when changing the pressure drop along them. If this is not so, the stability of the packing is affected on changing the pressure drop, which destroys the column efficiency. All available polymeric tubes, such as PTFE, nylon or plastic tubes, show a definite pressure dependence of the tube diameter. Apart from this, polymeric materials, except PTFE, are easily attacked by organic solvents. For these reasons polymeric materials are unsuitable as column tube materials in HPLC. Recently, however, the application of a radial compressed PTFE column for preparative LC was reported (Waters Assoc.). 

Since the introduction of GC in the early 1950s, many different column types have been developed, as is widely documented by numerous column technology studies reported in the chemical literature. The column design is extremely important to the analytical performance and utility for different sample types and applications. The most important features include (a) type of column sorption material (in both physical and chemical terms), (b) column diameter, (c) column length, and (d) surface characteristics of a column tubing material. A proper combination of these column design features can often be crucial to a particular chemical separation. 

Column Tubing. The chromatographic column is contained in a tubing, the composition of which may have a dramatic effect on the separation process, because the sample components may also interact with the walls of the tube. Some of the materials used for columns are... 

Inlets for syringe sampling are divided kito two main categories one for packed-column and the other for capiHary-column devices. Eor packed columns, all material kijected is carried by the mobile phase onto the column. The inlet is usually an open tube, but sometimes, albeit rarely, the inlet itself may be packed, eg, to assure that the first centimeters of the column do not become contaminated with degradation products or nonvolatile materials that may affect the efficacy of the column. 

Figure 1 The column tube end is drawn to a fine tip. To prevent fouling the ion source with packing material a small amount of coarser HPLC material is placed inside the tip. By coating with high-temperature epoxy glue (EPO-TEK 353ND) the tip is mechanically protected. This design gives the best chromatographic results. A 30-cm packed column with 3 ym Spherisorb ODS particles gives almost 5 x 10 theoretical plates (3). The separation impedance (unretained solute time per plate multiplied by the pressure drop per plate and divided by the viscosity of the eluent) has been calculated as 750.

The column consists of a stainless steel tube which for analytical work may be up to 20 cm in length and in the region of 5 mm internal diameter, although the tendency in recent times is for even narrower columns. For preparative operations the column length may be up to 50 cm and the internal diameter up to 20 mm. The column-packing material is of a very uniform particle size, and may be, for example, 10, 7, 5 or 4/im the smaller particle sized material is preferred for analytical applications, and the larger particle size for preparative work. The... 

Extensive experience of the preparation of bonded-silica columns for CEC has suggested to us that all packing methods have similar problems associated with the fragility of the fused-silica tubing material, especially at the Mt and detection window, where the polyimide coating had been removed. A less commonly met effect is the production of loosely packed silica particle beds with voids, giving rise to unstable currents. Approximately 70% of capillaries could be successfully packed by an experienced operator, with approximately 80% of packed and tested columns giving satisfactory CEC [23],... 

Extracts from all samples were analyzed by gas chromatography as described by Hindin, May, and Dunstan (5). After the residue had been taken up in a measured volume (0.1 or 1.0 ml.) of petroleum naphtha, a 10-/Jiter aliquot was injected into a Beckman temperature programmer coupled with a Dohramann microcoulometric titration detector. The column-packing material used for the separation of the insecticides was 5% by weight of EPON 1001 on 60/80-mesh acid-washed, flux-calcined diatomite (Chromosorb P). This material was packed in aluminum tubing % inch in o.d. by 3 feet. 

Set stirrer going and heat rapidly until temperature is about 15° below the melting-point. Meanwhile introduce a f to f-inch column of the powdered sample (previously dried to remove moisture) into a tube and tap and tamp down gently. Attach the tube to the thermometer by a rubber ring so that the center of the column of material is level with the center of the thermometer bulb, and replace thermometer as before. Reduce the heat so that the temperature rises 1° in two or three minutes. The slower rate should be adopted if several determinations are to be made at the same time. 

To prevent an undesirable degradation of the compounds to be analyzed, glass columns have mostly been used for gas chromatography of alkaloids because they are indifferent to the compounds. Possible catalytic decomposition of sensitive compounds and adsorption phenomena caused by metal columns, e.g. copper, aluminium and stainless steel, may, however, be eliminated in some cases by a simple coating of the tubing material with the stationary phase... 

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