Connectors, capillary columns

Apparatus Gas chromatograph with flame ionization detector (Flewlett-Packard 5890 Series n, or equivalent) equipped with a 5- xL syringe for 0.32-mm (id) columns. Automatic sampler (HP 7673, or equivalent). Chromatographic data system or integrator (HP 3365 Series II software, or equivalent). Retention gap, deactivated fused silica, 1-mm x 0.32-mm (id) with capillary column connectors. DB 5-HT,... 

Figure 20-25. Direct-connect capillary column connectors. (Courtesy - Alltech Associates Inc., Deerfield, IL)...

Figure 5.2. Schematic diagram of a standard liquid chromatograph modified for use with a packed capillary column. Typical pump settings are 300-400 p,l / min with flow splitting of 1 2000 to give a column flow of 150-200 nl / min. The microinjection valve has a 40 nl internal loop and an additional T.IO split creates an injection volume of 2-3 nl (larger volumes can be injected by on-column focusing with gradient elution separations). The detector uses a U- or Z-shaped flow cell with a 3 nl volume and 8 mm path length. Fused-silica capillary tubing with an internal diameter < 20 pm and zero-dead-volume connectors are used for column connections. (From ref [8j. American Chemical Society).

An integrated circuit connector pad, consisting of a polymer film 22 acting as a carrier for an array of metal tubes 24 which extend through the film and protrude from each side, is continuously dipped in molten indium until the tubes are filled with indium by capillary action. The indium-filled tubes are affixed on a read-out chip. Next, the original metal tubes are etched away and the carrier is lifted off. Finally, the detector chip is aligned in position with the indium columns and the read-out chip and the detector chip are joined by pressure welding. 

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]. 

A recent development is the direct-connect capillary connector shown in Figure 20-25. Two pieces of capillary tubing can be connected without tools or other fittings and be gas tight. Simply push the end of the tubing into the connector. You must heat them to 150 "C to complete the seal. The ends must be cut square to get a goodfit. If the column is old, dip the end into pentane before inserting it. 

Figure 3.18. Thermal modulators for comprehensive two-dimensional gas chromatography. The slotted moving heater (left) and longitudinally modulated cryogenic trap (right). Components 1 = injector 2 = first dimension column 3 = slotted heater 4 = stepper motor 5 = press fit connector 6 = thick film modulator capillary 7 = second dimension column 8 = detector. (Adapted from ref. [168 ] and [225] Elsevier).

You have to remove the column and connect the capillary from the injector directly to the detector using a dead volume-free connector. You now have to inject a U V-detect-able solute, for example 1 xl of acetone or simply your standard mixture at a low flow setting, for example 0.2 ml/min. If you use a recorder or an integrator, you should set the paper speed at its maximum value for an exact measurement. The injected solute will result in a peak. Please measure the elution time at the apex (see Fig. 9-1). 

Pentoney, S. L., Huang, X. H., Burgi, D. S., and Zare, R. N., Online connector for microcolumns— Application to the on-column ortho-phthaldialdehyde derivatization of amino-acids separated by capillary zone electrophoresis. Anal. Chem., 60, 2625, 1988. 

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