Micropacked columns for

Open-Tubular and Micropacked Columns for Supercritical Fluid Chromat Brian Jones... 

Sternberg, R., Szopa, C., Coscia, D., Zubrzycki, S., RauUu, E, Vidal-Madjar, C., Niemaun, H., Israel, G. (1999) Gas chromatography in space exploration—capillary and micropacked columns for in situ analysis of Titan s atmosphere./oitmo/ of Chromatography A,846(l-2), 307-315. 

Electrochemical detectors for liquid chromatography have reached a level of maturity in that thousands of these devices are used routinely for a variety of mundane purposes. Nevertheless, the technology is advancing rapidly in several respects. Multiple electrode and voltammetric detectors have been developed for more specialized applications. Small-volume transducers based on carbon fiber electrodes are being explored for capillary and micropacked columns. Recently, electrochemical detection has also been coupled to capillary electrophoresis [47]. Finally, new electrode materials with unique properties are likely to afford improved sensitivity and selectivity for important applications. 

One of the drawbacks of using modifiers is their response in some of the detectors. The flame ionization detector (FID) is very popular with capillary and micropacked columns in SFC because of its near-universal response and high sensitivity and the lack of response of CO2 as the most popular mobile phase. The low mass flow rate of the mobile phase in small columns allows for a direct interfacing of the column to the FID and other detectors without flow splitting or back-pressure regulation. 

In the later work," the micropacked GC column was replaced with a 50-m-long narrow-bore capillary column with probably more than 10 times as many theoretical plates. Comparing the P2 profile (micropacked GC column) in Figure 7.8 with the P2 profile (narrow-bore capillary GC column) in Figure 7.9 illustrates the tremendous additional amount of detail that can be obtained through the use of high-resolution capillary columns for the separation of pyrolyzates. 

GC. Today, there are no commercial sources for instruments designed for open tubular columns, although packed column and micropacked column instruments can be adapted for this use. 

Packed columns of different diameters have been used in SFC. Large-diameter columns (4.6 nun i.d.) provide high sample capacities, and, because of the relatively large flow of mobile phase, variable end column restrictors can readily be employed. Such restrictors make it possible to programme the flow of mobile phase, keeping the pressure constant. It is possible to use a variable end column restrictor also with micropacked columns (Janak et al, 1992b Janssen, Rijks and Cramers, 1990) but that is quite complicated and systems for this are not commercially available. 

Micropacked columns are available with most of the bonded-phase packings used in HPLC. Porous and non-porous silica particles are optionally functionalized with covalently ound silanes or other strongly adsorbed materials. ALkyl-bonded silicas produce separations, generally based on solute volatility, but with the potential for selectivity differences based on interaction with silanol groups. Underivatized silica is popular for petroleum separations of aliphatic and aromatic hydrocarbons. Silver-ion-containing silica columns are selective for olefin separations. Huoroalkyl-bonded... 

Most chemically bonded silicas can be used up to stationary temperatures of about 250 C. HPLC sorbents of this type are successfully used in capillary micropacked columns (see, for example,... 

Fig. 5-14 [63] shows van Deemter plots obtained for columns packed with 5, 10 and 30 p,m oc-tadecylsilica. The smaller the particle the less was the dependence of linear velocity on the theoretical plate height. Chromatograms of aliphatic and aromatic hydrocarbons are shown in Fig. 5-15 [65]. Use of the octadecylsilica in micropacked columns allows improvement of the efficiency of capillary packed columns. No tailing was observed. Application of these sorbents to gas chromatography, especially in packed capillary columns, is, in our opinion, a very promising direction [55, 63-69]. We also think that this type of modified adsorbents can be successfully used in gas adsorption on open capillary columns.

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