Column, capillary phase

Carmine extracted from cochineal insects is one of the most used natural colorings for beverages and other foods. Some representative articles refer to isolation and spectrometric analysis or the use of HPLC or capillary electrophoresis (CE) to separate and characterize all cochineal pigments. Its active ingredient, carminic acid, was quantified by rapid HPLC-DAD or fluorescence spectrometry. Carminic acid, used as an additive in milk beverages, was separated within 9 min using a high-efficiency CE separation at pH 10.0 after a previous polyamide column solid phase extraction (SPE), ... 

FIGURE 7.13 Two-dimensional separation of tryptic digest of BSA in simple 2D-HPLC. Capillary monolithic silica-C18 column (0.1 mmi.d., 10 cm) was used as 2nd-D column. Mobile phase for 2nd-D gradient started with 0% B at 0.5 min, increased to 50% B at 3.3 min, to 100% B at 3.5 min, then returned to the initial condition and held for the last 0.5 min. Flow rate 3.0 pL/min in capillary, and 2 mL/min at the pump. Other conditions are similar to those for Figure 7.11 (reproduced from the reference, Kimura et al. (2004) with permission from Wiley). 

Gas-Liquid Chromatography. In gas-liquid chromatography (GLC) the stationary phase is a liquid. GLC capillary columns are coated internally with a liquid (WCOT columns) stationary phase. As discussed above, in GC the interaction of the sample molecules with the mobile phase is very weak. Therefore, the primary means of creating differential adsorption is through the choice of the particular liquid stationary phase to be used. The basic principle is that analytes selectively interact with stationary phases of similar chemical nature. For example, a mixture of nonpolar components of the same chemical type, such as hydrocarbons in most petroleum fractions, often separates well on a column with a nonpolar stationary phase, while samples with polar or polarizable compounds often resolve well on the more polar and/or polarizable stationary phases. Reference 7 is a metabolomics example of capillary GC-MS. 

Several manufacturers offer GC-FT IR instruments with which a vapor-phase spectrum can be obtained on nanogram amounts of a compound eluting from a capillary GC column. Vapor-phase spectra resemble those obtained at high dilution in a nonpolar solvent Concentration-dependent peaks are shifted to higher frequency compared with those obtained from concentrated solutions, thin films, or the solid state (see Aldrich, 1985). 

Three types of columns can be used in gas chromatography. From the oldest to the most recent, these are packed columns, capillary columns and wide bore or 530 columns (which have a 530 pm inner diameter) (shown in Fig. 2.6). For packed columns, the stationary phase is deposited onto a porous support. For the latter two, the stationary phase is deposited onto or bound to the inner surface of the column. The performance of these columns differs. 

Up to now, most efforts have been directed towards the preparation of uniformly sized spherical MIP particles in the micrometre range. This is the obvious consequence of the need for this kind of materials as fillers for high-performance chromatographic columns, capillaries for electrophoresis, cartridges for solid-phase extractions and other applications requiring selective stationary phases. Additionally though, strategies for the preparation of other more sophisticated MIP forms, such as membranes, (nano)monoliths, films, micro- and nanostructured surfaces etc. 

H. G. J. Mol, J. Staniewski, H.-G. Janssen and C. A. Cramers, Use of an open-tubular trapping column as phase-switching interface in on-line coupled reversed-phase hquid chromatography-capillary gas chromatography , J. Chromatogr. 630 201 -212 (1993). 

L. G. McLaughlin and J. D. Henion, Determination of dexamethasone in bovine tissues by coupled-column normal-phase high-performance liquid chromatography and capillary gas chromatography-mass spectrometry ,./. Chromatogr. 529 1-19 (1990). 

Several techniques have been used to overcome the problem of low column loadings on capillary columns. Capillary columns have also been used after preconcentration of alkyl derivatives on a wide-bore fused silica column103 or by solid-phase microextraction (SPME).106... 

The medium-film thickness is about 0.3-0.6 pm and generally offers the best compromise of sample capacity, retentivity, and phase stability. The phase ratio determines the capacity of the column and influences its retentivity of solutes. The phase ratio (j8) can be defined as the ratio of the inner column radius to that of the product of twice the stationary-phase film thickness or 0 = r/2df. We can now also use phase ratios to group film thicknesses and now say that thick-film columns have phase ratios of less than about 80. (In capillary SFC the typical stationary-phase film thicknesses are 0.1-0.3 pm.) The effective phase ratio can change in capillary SFC, depending on the characteristics of the stationary phase and the operating density [57]. The change in phase ratio can be attributable to a swelling of the stationary phase under certain SFC conditions. 

Columns Capillary columns, which are usually made of fused silica, have a 0.2- to 0.53-mm id and are 5 to 30 m long. The liquid or stationary phase is 0.1 to 1.0 jxm thick, although nonpolar stationary phases may be up to 5 p,m thick. 

Figure 14 Separation of the test mixture using a step voltage gradient and a short packed column. Capillary 75 mm i.d., 8 cm packed with Dionex AS9-HC (8.5 cm to detector, 34.5 cm total). Mobile phase 2.5 mM hydrochloric acid (titrated to pH 8.05 with Tris). Flow is a combination of 10-bar pressure and EOF with -30 kV added at 1.3 min. All other conditions as given in Figure 1. (Reprinted from Ref. 75, with permission.)...

In a study presented by Jinno et al. [124], packed column capillary electrochromatography, open-tubular CEC, and microcolumn liquid chromatography using a cholesteryl silica bonded phase have been studied to compare the retention behavior for benzodiazepines. The results indicated that CEC was a promising method, as it yielded better resolution and faster analysis than microcolumn LC for benzodiazepines. Similar selectivity to HPLC was noted, except for a few solutes that were charged under the separation conditions. Columns packed with the ODS and cholesteryl phases were compared and showed totally different migration orders of the analytes. The retention on the cholesteryl silica sta-... 

As with any form of chromatography, the separating efficiency of capillary columns in gas chromatography is strongly dependent on the column stationary phase, carrier gas flow rate, and temperature. Because of the high separation efficiency of capillary columns, only a limited number of stationary phases can be substituted for the numerous phases used in most packed column applications. The choice of a stationary phase is commonly dictated by experience. A phase that has been successfully used by others is usually a good choice. Fre-... 

A polar stationary phases such as ODS and TMS and polar such as CN, diol, or NO2 have been successfully applied to the separation of monosaccharides Separation of maltodextrin derivatized with trifluoroacetic anhydride using FID and a CN packed column Capillary supercritical fluid chromatography-MS is well suited to confirm the identity of the TMS derivative of inositol triphosphate Chiral analytes Enantioseparation... 

This type of column has become the most widely used because of its superior resolving power for complex mixtures compared to that of a packed column. Capillary columns are typically 5 to 50 metres long and between 0.1 mm and 0.60 mm internal diameter. A thin him (0.1 to 5 /zm thick) of the liquid stationary phase is coated or bonded onto the inner wall of the tube (hence the alternative description of wallopen tubular or WCOT columns)... 

A wide variety of stationary phases and bonded-phase particles for SFC are available. Capillary columns are coated with substituted and cross-linked polysiloxanes, which exhibit good inertness, efficiency, and stability. There are three main classes of capillary column stationary phases for SFC apolar, polarizable, and polar. 

Apart from the sample material the following capillary columns (stationary phases) are suitable for flavour analysis ... 

One of the most valuable usage for the McReynolds system is to identify stationary phases. For example, SE-30 and DC-200 or OV-101 are very similar stationary phases (with different names but practically similar retention patterns). This system also allow for a rapid selection of phases with different retention properties, to separate compounds that have different functional groups, such as alcohol from ketones, aromatic fi-om aHphatics, or saturates from unsatvaates. It shoxdd be noted that the McReynolds system is not only apphed to packed columns, but also to the selection of capillary column stationary phases. 

A large variety of normal phase HPLC columns (packed type) or GC columns (capillaries) are used. These two types of columns are complementary. For a packed column of HPLC type, the high flow rate of the supercritical mobile phase will render detection by FID or coupling with a mass spectrometer more difficult. Adding a modifier to the supercritical fluid would have the same effect. 

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