Stationary phase capillary columns

In general, the longer a chromatographic column, the better will be the separation of mixture components. In modem gas chromatography, columns are usually made from quartz and tend to be very long (coiled), often 10-50 m, and narrow (0.1-1.0 mm, internal diameter) — hence their common name of capillary columns. The stationary phase is coated very thinly on the whole length of the inside wall of the capillary column. Typically, the mobile gas phase flows over the stationary phase in the column at a rate of about 1-2 ml/min. 

For carrying out of given researches method of synthetic pyrethroids determination in air has been developed. Chromatographic behaviour is investigated and optimum conditions of the synthetic pyrethroids analysis with application of capillary column with stationary phase DB-5 and electron-capture detector are selected. 

Fused silica capillary columns of various internal bores and of lengths in the range 25 to 50 m are mainly employed for analytical separations. A variety of polar and non-polar column types are available including those open tubular types with simple wall coatings (WCOT), those with coatings dispersed on porous solid-supports to increase adsorbent surface area (SCOT) and porous layer open tubular (PLOT) columns. Important stationary phases include polyethylene glycol, dimethylpolysiloxane and different siloxane copolymers. Various sample introduction procedures are employed including ... 

Keywords. Capillary electrochromatography, Theory, Electroosmotic flow, Separation, Instrumentation, Column technology, Stationary phase, Conditions, Applications... 

Fused silica capillary column containing stationary phase... 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

It is seen from equation (7) that the longitudinal diffusion term is a function of (k ) the capacity factor of the solute. While this may be a significant effect in LC capillary column systems, where the film of stationary phase is continuous along the length of the column, it will not be so in a packed column. The stationary phase in a packed column is not only broken into segments between each particle but also between each pore in each particle so free diffusion would be impossible. It follows that the longitudinal diffusion term for packed columns will be independent of the k of the solute or, very nearly so, and the experimental support for this will be discussed in the next chapter. 

Figure 4. Separation of selected aromatic amines on a basic WCOT glass capillary column with stationary phase Carbo wax 20 M solvent, 2-butanone. Peak identities 1, 1,2-diaminotoluene 2, 2,4-diaminotoluene 3, N,N-dipheny famine 4, 1-aminonaphthalene 5, 2-aminonaphthalene 6, 2,4-diamino-l-methoxybenzene.

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. 

For capillary columns, numerous stationary phases are known [e.g. 39] but a few of them are very frequently utilized because of their ability to separate a variety of compounds. Such phases are... 

The separation of essential oil components is usually carried out by GC with fused-silica capillary columns. The properties and conditions of columns used are variable, depending on the polarity of the components to be separated. The most used columns include stationary phases such as DB-1, Carbowax, OV-1, OV-101, PEG 20M, BPS, and DB-5, which cover a wide range of polarities. Column lengths normally range from 25 to 100 m, and stationary phase film thickness ranges from 0.2 to 0.7 pm. Elution of components is usually performed with a temperature gradient ranging from 50°C to 280°C. 

The pioneering gas-liquid chromatographic studies in the early 1950s were carried out on packed columns in which the stationary phase was a thin film of liquid retained by adsorption on the surface of a finely divided, inert solid support. From theoretical studies made during this early period, it became apparent that unpacked columns having inside diameters of a few tenths of a millimeter could provide separations that were superior to those of packed columns in both speed and column efficiency. In such capillary columns, the stationary phase was a film of liquid a few tenths of a micrometer thick that uniformly coated the interior of capillary tubing. In the late 1950s, such open tubular columns were constructed the predicted... 

In open tubular columns, the stationary phase is held on the inner surface of a capillary, whereas in packed columns, the stationary phase is supported on particles that are contained in a glass or metal tube. Open tubular columns contain an enormous number of plates that permit rapid separations of closely related species. They suffer from small sample capacities. 

A 30 to 50 m fused silica capillary column with a 5% phenyl-95% methyl-polysiloxane chemically bonded stationary phase (DB-5, CP Sil-8, HP Ultra 2, PTE-5) is very often used, while several oven temperature programs have been applied for PCB analysis. Table 18.7 shows a selection of combinations of column lengths, stationary phases, oven temperature programs, and detectors. Table 18.8 shows the stationary phase composition of the capillary columns listed in Table 18.7. Cochran et al. " have reviewed the most recent developments for the capillary GC of PCBs with detailed lists of PCB retention times on common capillary columns. 

Separation number (SN) is a practical, alternative means of describing the separating capabilities of a capillary column. SN shows the ability of a given column and stationary phase to separate a mixture into its components with a resolution of 1.0 between the peaks. SN is calculated from retention times and peak widths of two consecutive homologous n-alkanes having Z and Z + 1 carbon atoms and indicates the number of component peaks that can be resolved R 1.0) between the two alkanes in a given part of the chromatogram. 

OV-11, OV-17, OV-101, QF-1, SE-54, SP-2250, EGA, Dexsil-300, and others) have been used successfully in packed columns. Extensive reviews on detectors, column supports, stationary phases, reproducibility, and separation efficiency of TAB, HFB, and TMS derivatives have been published (Husek and Macek, 1975 Blackburn, 1978) and require no further elaboration. However, the capillary columns deserve further mention. The use of various stationary phases, especially SE-30, SE-54, SE-2100, OV-1, OV-17, OV-101, OV-210, EGA, and Carbowax 20M, have been utilized OV-101 (Chauhan et al., 1982 Chauhan and Darbre, 1982 Moodie, 1981 Husek, 1982 Desgres et al., 1979), SE— 54 (Gajewski et al., 1982), and SE-30 (Poole and Verzele, 1978) are apparently superior m terms of separability, low background noise, and low column bleed... 

In practice, for packed columns the stationary phase is not continuous along the length of the column, as was implicitly assumed in the derivation of Equation [3.35], but is broken into discrete portions surrounding the stationary phase particles and even among different pores within a given particle. Accordingly diffusion within the stationary phase does not occur to any extent for packed columns within typical elution times, so this contribution is usually negligibly small relative to that from diffusion in the mobile phase, i.e., Hl is almost independent of k. This is not necessarily the case, however, for capillary columns in which the stationary phase is coated as a continuous film on the walls such columns are of course common for GC, but are almost never used for EC. 

Both packed and open capillary columns (both WCOT and SCOT columns) can be used for GLC separations. In packed columns and SCOT columns, the high-boiling liquid stationary phase is distributed evenly on a solid totally porous particle, called the support or the matrix. In WCOT columns, the stationary phase is distributed as a thin film on the inner wall of a capillary, which is often fused silica. 

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