Types of columns and packings

Bruun column. A type of all-glass bubble-cap column. 

Dufton column. A plain tube, into which fits closely (preferably ground to fit) a solid glass spiral wound round a central rod. It tends to choke at temperatures above 100° unless it is lagged (Dufton J Soc Chem lnd (London) 38 45T 1919). 

Hempel column. A plain tube (fitted near the top with a side arm) which is almost filled with a suitable packing, which may be of rings or helices. 

Oldershaw column. An all-glass perforated-plate column. The plates are sealed into a tube, each plate being equipped with a baffle to direct the flow of reflux liquid, and a raised outlet which maintains a definite liquid level on the plate and also serves as a drain on to the next lower plate [see Oldershaw lnd Eng Chem (Anal Ed) 11 265 1941], 

Todd column. A column (which may be a Dufton type, fitted with a Monel metal rod and spiral, or a Hempel type, fitted with glass helices) which is surrounded by an open heating jacket so that the temperature can be adjusted to be close to the distillation temperature (Todd lnd Eng Chem (Anal Ed) 17 175 1945). 

Types of columns and packings. A slow distillation rate is necessary to ensure that equilibrium conditions operate and also that the vapour does not become superheated so that the temperature rises above the boiling point. Efficiency is improved if the column is heat insulated (either by vacuum jacketing or by lagging) and, if necessary, heated to Just below the boiling point of the most volatile component. Efficiency of separation also improves with increase in the heat of vaporisation of the liquids concerned (because fractionation depends on heat equilibration at multiple liquid-gas boundaries). Water and alcohols are more easily purified by distillation for this reason. 

Condensers. Some of the more commonly used condensers are  

Air condenser. A glass tube such as the inner part of a Liebig condenser (see below). Used for liquids with boiling points above 90°. Can be of any length. 

Coil condenser. An open tube, into which is sealed a glass coil or spiral through which water circulates. The tube is sometimes also surrounded by an outer cooling Jacket. A double coil condenser has two inner coils with circulating water. 

Double surface condenser. A tube in which the vapour is condensed between an outer and inner water-cooled jacket after impinging on the latter. Very useful for liquids boiling below 40°. 

---

CEC columns are generally made of fused-silica tubing, usually packed with the appropriate stationary phase. Today, the most commonly used CEC columns have i.d. of 100 p,m or less, with 50 and 75 p,m i.d. being the most popular. The stationary phase is retained in the column by two frits. Column designs can be categorized into two major types OT columns and packed structures, which include packed columns, monolithic columns, and microfabricated stractures (open or continuous beds). Packed capillary columns are most commonly used, as has been demonstrated in numerous papers [9-11]. They can be subdivided into three different categories columns packed with particles, columns with continuous beds fabricated in situ creating a rod-like monolithic structure, and columns with immobilized or entrapped particulate materials. 

Modes of HPLC other than GPC can be used to evaluate polymer mixtures, copolymer composition, and to analyze additives. As indicated in Fig. 8 and in Secs. II.A and II.D, for this work a number of changes are made to the system, especially the type of column and detection methods. The mechanism of separation is no longer exclusion, in which no adsorptive interaction between the sample components and the column packing material is tolerable. Instead, there is deliberate adsorptive interaction between the samples and the column packing in order to achieve separations based on differences in chemical composition of the sample components, independent of molecular size. Sec. III.C. 

The separation of close boiling components in a mixture has been accomplished commercially by cascading several evaporations and condensations of such mixtures in a device known as a distillation or rectification column. There are two types of columns, namely, packed columns and plate columns. The former are vertical cylinders filled with a variety of packings that provide a large surface area per unit volume to promote maximum contact between the downward liquid flow and the upward vapor flow. Since this type of column can encounter poorer vapor-liquid contact than the plate column, it is only seldomly used in cryogenic separation systems. 

It is a common procedure to assume certain conditions for the chromatographic system and operating conditions and, as a result, simplify equations (20) and (21). However, in many cases the assumptions can easily be over-optimistic, to say the least. It is necessary, therefore, to carefully consider the conditions that may allow such simplifying procedures and take steps to ensure that such conditions are carefully met when such expressions are used in practice. Now, the relative magnitudes of the resistance to mass transfer terms will vary with the type of columns (packed or capillary), the type of chromatography (GC or LC) and the type of particle, i.e., porous or microporous (diatomaceous support or silica gel). 

The Shodex GPC KF-600 series is packed with 3- im styrene-divinylbenzene copolymer gels in a column having a volume of about one-third compared to standard-types of columns, which are best suited for reducing the organie solvents eonsumption, shortening the analysis time, and lowering the detection limit (Table 6.5). 

Three different types of columns packed with gels of different pore sizes are available. Columns should be selected that are suitable for the molecular weight range of specific samples, as each type has a different exclusion limit (Fig. 6.41, page 215). Bovine serum albumin (BSA), myoglobin, and lysozyme show good peak shapes using only 100 mM of sodium phosphate buffer as an eluent. There is no need to add any salt to the eluent to reduce the ionic interaction between protein and gel. 

Gels made in this way have virtually no usable porosity and are called Jordi solid bead packings. They can be used in the production of low surface area reverse phase packings for fast protein analysis and in the manufacture of hydrodynamic volume columns as well as solid supports for solid-phase syntheses reactions. An example of a hydrodynamic volume column separation is shown in Fig. 13.2 and its calibration plot is shown in Fig. 13.3. The major advantage of this type of column is its ability to resolve very high molecular weight polymer samples successfully. 

Fair reports that the data for mass transfer in spray, packed, and tray columns can be used for heat-transfer calculations for these columns. The pressure drop in these types of columns is usually quite low. 

The analysis demonstrates the elegant use of a very specific type of column packing. As a result, there is no sample preparation, so after the serum has been filtered or centrifuged, which is a precautionary measure to protect the apparatus, 10 p.1 of serum is injected directly on to the column. The separation obtained is shown in figure 13. The stationary phase, as described by Supelco, was a silica based material with a polymeric surface containing dispersive areas surrounded by a polar network. Small molecules can penetrate the polar network and interact with the dispersive areas and be retained, whereas the larger molecules, such as proteins, cannot reach the interactive surface and are thus rapidly eluted from the column. The chemical nature of the material is not clear, but it can be assumed that the dispersive surface where interaction with the small molecules can take place probably contains hydrocarbon chains like a reversed phase. 

Five types of columns are routinely used in gas chromatography classical packed columns with internal diameters greater than 2 mm containing particles in the range 100 to 250 micrometers micropacked columns having diameters less than 1 mm with a packing density similar to classical packed columns (dp/d less than 0.3, where dp is the particle diameter and d the column diameter) packed capillary lumns have a column diameter less than 0.5 mm and a packing density less than classical packed columns (dp/d 0.2-0.3) SCOT columns (support-coated open... 

Thin-layer chromatography (TLC) is a type of liquid chromatography in which the stationary pease is in the form of a thin layer on a flat surface rather than packed into a tube (column). It is a member of a family cf techniques that include some types of electrophoresis and paper chromatography, more generally referred to as planar chromatccraphy. Since we will not discuss electrophoresis in this section, and since TLC has virtually superseded paper chromategr pby in most analytical... 

Unfortunately, the fractionating column you usually get is not a bubble-plate type. You have an open tube that you fill with column packing (see Class 3 Fractional Distillation ) and noplates. The distillations up this type of column are not discreet, and the question of where one plate begins and another ends is meaningless. Yet, if you use this type of column, you do get a better separation than if you used no column at all. It s as if you had a column with some bubble-plates. And if your distilling column separates a mixture as well as a bubble-plate column with two real plates, you must have a column with two theoretical plates. 

---