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as the 'state of the art' column, in fact, due to certain sampling problems, the packed column may have the edge on the capillary column for quantitative accuracy. Nevertheless, because of its speed and high resolution, the capillary column is by far the most popular in current use in gas chromatography.   The capillary column was invented by Golay, the theory of which was presented at the 1958 Symposium on Gas Chromatography and published in 1958 (1). The efficiencies provided by the capillary columns were, at that time, startling, to say the least. It will be seen when the theory of capillary columns is considered, the plate height of a capillary column is not very different from that of the packed column, the main advantage of the capillary column being its low flow impedance. As result of its greater permeability relative to the packed column, much longer column scan be used thus, providing much higher efficiencies. In addition, because there is no multipath term (see

History of Capillary Columns   There were no commercial capillary columns available in 1958 and all operational columns were 'home made'. In fact, the basic characteristics of capillary columns and their operating conditions were determined, almost exclusively, using these home made columns. The first columns were made from copper capillary 1/16 in. O.D. and 0.010 I.D. which was readily available commercially and relatively inexpensive. The standard length then was 100 ft and the stationary phase was coated on the walls of the column from a solution

is available in most chromatographs. By using a syringe with a long needle, the tip can be made to penetrate past the liner and discharge its contents directly into the column packing. This procedure is called 'on-column injection' and, as it reduces peak dispersion on injection and thus, provides higher column efficiencies, is often the preferred procedure.   Open Tubular Column Injection Systems Due to the very small sample size that must be placed on narrow bore capillary columns, a split injection system is necessary, a diagram of which is shown in figure 8. Figure 8 The Split Injection System The basic difference between the two types of injection systems is that the capillary column now projects into the glass liner and a portion of the carrier gas sweeps past the column inlet to waste. As the sample passes the column opening, a small fraction is split off and flows directly into the capillary column, ipso facto this

columns. In any event, most chromatographers do not want the trouble of coating their own columns and prefer to purchase proprietary columns. Very difficult separations can be achieved using the capillary column, and in a relatively short time. An example of the separation of a complex mixture on a capillary column is shown in figure 17. The column used was designated as a VOCOL column and was 60 m long, 0.75 mm I.D. and carried a film of stationary phase 1.5 micron thick. The column was held a 10˚C for 6 minutes and then programmed to 170˚C at 6˚C per minute. The carrier gas was helium at a flow rate 10 ml/min. The detector employed was the FID. This chromatogram demonstrates the clear advantages of capillary columns over packed column. Not only does the column produce exceeding high efficiencies but they are also achieved with reasonable separation times. Open Tubular Column Types Open Tubular columns are broadly split into two

nbsp;      or,                     (56) It is seen that, in a similar manner to the packed column, the optimum mobile phase velocity is directly proportional to the diffusivity of the solute in the mobile phase. However, in the capillary column the radius (r) replaces the particle diameter (dp) of the packed column and consequently, (uopt) is inversely proportional to the column radius

In addition it is seen, from equation (56), that the expression for uopt is very similar to that for a packed column but the expression for Hmin. is much simpler as it is devoid of the (A) term from the multipath effect. Due to the relative simple, and precisely defined, geometry of the capillary column it contains no arbitrary constants involved with the packing quality of the column such as (g) and (l). As a consequence, the properties of the capillary column can be explored further in a relatively straightforward manner. In the following treatment an LC capillary column will be considered despite, at this time, equipment for the efficient use of LC capillary columns is not available. From Poiseuille's Equation, describing the flow of liquid through an open tube, operating at the optimum velocity,            &