Micropacked columns

The advantages of micropacked columns have been overtaken by the development of thick film wide bore WCOT capillary columns with internal diameters of 0.5-0.7 mm and up to 5.0 pm stationary phase films (section 5.5). 

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Selected applications of coupled SEE-SEC consider the analysis of tocopherols in plants and oil by-products (65) or the analysis of lipid-soluble vitamins (66) by using a dynamic on-line SEE-SEC coupling, integrated in the SE chromatograph, based on the use of micropacked columns. 

E. Ibanez, M. Heiraiz and G. Reglero, On-line SEE-SEC coupling using micropacked columns , J. High Resolut. Chromatogr. 18 507-509 (1995). 

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... 

COMPARISON OF WCOT AND MICROPACKED COLUMNS HAVING SIMILAR PHASE RATIOS... 

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. 

Packed Columns. If the stationary phase is a liquid, it is held in the column on an inert solid support, which will still appear dry. This support, or an active solid, is the material packed in the column. The nature of these packed beds was discussed in Chapter 2. Theory predicts that improved performance should result from the use of small particles, so some attempts have been made to pack them into columns. Because the diameter of these columns is usually small too, they have been called packed capillaries or, more generally, micropacked columns. Packed columns with a dpldc 0.3 have been put in this classification and reviewed.5 Some very high efficiencies have been obtained, but sometimes at the expense of very high inlet pressures. 

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

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. 

The small internal volume and low mobile-phase mass flow rates in capillary and micropacked column SFC place significant demands on the injection system and... 

Capillary Chromatography Including Glass Micropacked Columns Kaiser, R. E., Ed. Institute fur Chromatographie Bad Durkheim, Germany, 1975 p. 1. 

Besides the stationary-phase selectivity, the phase ratio (volume of the mobile phase/volume of the stationary phase) is an important consideration in practical chromatography. Thus, within the available arsenal of GC columns, the efficiency increases in the following direction packed column < micropacked column < support-coated open tubular column (or wide-bore capillary column) < conventional... 

While the developments in capillary GC were slow in coming in the late 1960 s, many researchers then considered the support-coated open tubular and micropacked columns to be viable alternatives to the conventional capillaries. Although some interesting results were reported about 10 years ago [94,95] on the performance of such columns, they were largely overshadowed by the rapid advances in technology of wall-coated columns. The limited column permeability of micropacked columns and an excessive surface activity of support-coated open tubular columns are the major drawbacks of these column types. However, they may still offer a suitable compromise between sample capacity and column efficiency in certain special instances. 

Figure 5.4 Cross-section of GC columns, (a) in. packed column (b) thin film WCOT column (c) thick film WCOT column (d) in. micropacked column (e) PLOT column (f) SCOT...

Micropacked, packed capillary, and support coated open tubular (SCOT) columns are rarely used today, having been superceded by developments in WCOT and PLOT column technology. Micropacked columns have diameters less than 1 mm and a similar packing density to classical packed columns. Packed capillary columns have an internal diameter less than 0.6 mm and are packed with particles of 5-20 pm diameter. SCOT columns are capillary columns containing a liquid phase coated on a surface covered... 

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. 

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