Open tubular columns evaluation

Having established that a finite volume of sample causes peak dispersion and that it is highly desirable to limit that dispersion to a level that does not impair the performance of the column, the maximum sample volume that can be tolerated can be evaluated by employing the principle of the summation of variances. Let a volume (Vi) be injected onto a column. This sample volume (Vi) will be dispersed on the front of the column in the form of a rectangular distribution. The eluted peak will have an overall variance that consists of that produced by the column and other parts of the mobile phase conduit system plus that due to the dispersion from the finite sample volume. For convenience, the dispersion contributed by parts of the mobile phase system, other than the column (except for that from the finite sample volume), will be considered negligible. In most well-designed chromatographic systems, this will be true, particularly for well-packed GC and LC columns. However, for open tubular columns in GC, and possibly microbore columns in LC, where peak volumes can be extremely small, this may not necessarily be true, and other extra-column dispersion sources may need to be taken into account. It is now possible to apply the principle of the summation of variances to the effect of sample volume. 

The separation nuaber is the only column efficiency par2uaeter that can be deterained under teaperature progr2uued conditions [45,46]. The critical parameters that aust be standardized to obtain reproducible SM values for coluans of different length are the carrier gas flow rate and the temperature program. The SN is widely used as part of a standardized test method to evaluate the quality of open tubular columns for gas chromatography (section 2.4.3). 

EPA. 1990a. Application of open-tubular columns to SW-846 GC methods. In Test methods for evaluating solid waste. SW-846. Washington, DC U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. EPA/600/S4-90/021. 

Dhanesar, S.C., Coddens, M.E., and Poole, C.R, Evaluation of tetraalkylammo-nium tetrafluoroborate salts as high-temperature stationary phases for packed and open-tubular column gas chromatography, /. Chromatogr., 349, 249-265,... 

According to Scott the average linear velocity can be replaced by (4uq / [P -i- 1]) in Eq. (1.23) to permit evaluation entirely in terms of the outlet velocity [130]. If X = 0, y = 1, and dp = rc is substituted into Eq. (1.23) then this equation can be used as an alternative to Eq. (1.22) to account for band broadening in evaluating open tubular columns [121,130]. For gas-solid chromatography the stationary phase mass transfer... 

Packed columns coated with a wide variety of stationary phases are commercially available. Unlike open tubular columns they are easily prepared in the laboratory and many chromatographers prefer to prepare their own columns. Almost any liquid not restricted by its vapor pressure can be studied extending the scope of packed columns to stationary phases unavailable on open tubular columns as well as allowing gas chromatography to be used to obtain physicochemical properties of a wide range of materials evaluated as stationary phases. 

Purification on an open tubular column with silicagel and Sephadex LH 20 gave irreproducible losses in the first experiments. For the evaluation of possible errors during an analytical procedure it is unsuitable to involve a clean up step with uncomplete recovery from the beginning. For this reason, purification of samples will be a part of the investigations later in this project. 

When one is deciding what column geometry is optimal for trace analysis with unlimited sample volume, two additional points should be evaluated. First, to what extent does the analysis require accurate and reproducible injections Strict performance specifications may eliminate microbore columns from consideration. The accuracy and reproducibility of injection systems that deliver 0.1-, 0.2-, and 0.5-/xL samples have not been adequately characterized. Second, if the analyte of interest requires postcolumn derivatization, construction of a postcolumn reaction system that is compatible with the exceedingly small band volumes characteristic of microbore columns may be extremely difficult, but not impossible. Apffel et al. (28) developed and evaluated both packed-bed and open tubular postcolumn reactors for use with 1-mm i.d. analytical columns. Catecholamines were postcolumn derivatized with o-phthal-aldehyde and detected spectrofluorometrically. The 5-/zm particle... 

GC capillary coliunns have a uniform geometry and in the absence of a stationary phase H in is directly proportional to the column internal diameter dc and retention characteristics, k, of the stationary phase film including polar character and film thickness [9-11]. Column design may be evaluated for efficiency and optimum mobile phase velocity using the following equation for proposed by Golay when he developed the theory for open tubular (WCOT) columns [9] ... 

Liu, J., Dolnik, V., Hsieh, Y.-Z., and Novotny, M. Experimental evaluation of the separation efficiency in capillary electrophoresis using open tubular and gel-filled columns. Anal. Chem. 64,1328, 1992. 

Upnmoor and Brunner [7] evaluated a packed column SFC with a light scattering detector using a mobile phase of carbon dioxide modified with methanol for the chromatography of polymer additives. Moulder and co-workers [8] transferred eluent fractions from a packed capillary size exclusion chromatographic (SEC) column using a solvent vented interface to an open tubular CSFC column. The system was evaluated for the analysis of polymer additives. 

Evaluation of a Gas-Liquid Chromatographic Method for the Determination of Urinary Steroids Using High-Resolution Open-Tubular Glass Capillary Columns... 

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