Open tubular column testing

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). 

In practice, it is more difficult to optimize resolution as a function of the relative retentlvity than to optimize retention. Thus, unless the mixture is very complex or contains components that are particularly difficult to separate it may be possible to optimize a particular separation using the linear equation (1.72) as demonstrated by Bttre [177]. Figure 1.13 illustrates the relative change in peak position for a polarity test mixture with two identical, serially coupled open tubular columns, coated with a poly(dimethylslloxane) and Carbowax 20 M stationary phases, as a function of their relative retentlvity on the second column. The linear relationship predicted by equation (1.72) effectively predicts the relative peak positions and indicates that a nearly... 

Standardized Quality Test for Coated Open Tubular Columns... 

RELATIVE CONTRIBUTION (PERCENTAGE BASIS) OF MASS TRANSFER RESISTANCE IN THE MOBILE AMD STATIONARY PHASE TO COLUMN PLATE HEIGHT FOR A SERIES OF 0.32 mm I.D. OPEN TUBULAR COLUMNS USING UMDECAME AT 130 C AS THE TEST SOLUTE... 

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. 

The United States Pharmacopeia (USP) test (467) describes three different approaches to measuring organic volatile impurities in pharmaceuticals. Method I uses a wide-bore coated open tubular column (G-27, 5% phenyl-95 % methylpolysiloxane) with a silica guard column deactivated with phe-nylmethyl siloxane and a flame-ionization detector. The samples are dissolved in water and about 1 p is injected. Limits are set for benzene, chloroform, 1,4-dioxane, methylene chloride, and trichloroethylene. Methods V and VI are nearly identical to method I except for varying the chromatographic conditions. For the measurement of methylene chloride in coated tablets, the headspace techniques described above are recommended. 

Once the open tubular column has been properly installed into the gas chromatograph and tested to be leak free, set the column and detector gas flows. Before heating the column, allow the system to purge with carrier gas at ambient temperature for at least 30 min. 

Figure 1.13 separation of a polarity test aixture on two 25 x 0.25 iDit I.O. (df - 0.25 aicrometers) serially coupled open tubular coluims, coated with a bonded poly(diwethylsiloxane), column i, and stabilized Cari>owax 20 M, colunn 2, stationary phases. The... 

As a further test of the etched open tubular approach for the analysis of optical isomers, another column was fabricated based on the selector naphthylethylamine that had been attached to porous silica by the silanization/hydrosilation method for use in HPLC [70]. As in the HPLC experiments, this column was best suited for the resolution of the optical isomers of dinitrobenzoyl methyl esters of amino acids. The best separation (a = 1.14) was obtained for the alanine derivative. In addition, the peak symmetry and efficiency for the naphthylethylamine column was significantly better than that obtained on the cyclodextrin column. However, as shown in HPLC experiments, changes in the amino acid moiety (replacing alanine with valine, etc.) often results in a loss of chiral resolution. In the case of optical isomers, the separation mechanism in HPLC and CEC modes is identical since only interaction between the solute and the bonded phase can result in resolution of the enantiomers. 

In the test, a sample aliquot diluted with a viscosity-reducing solvent is introduced into the gas chromatographic system, which uses a nonpolar open tubular capillary gas chromatographic column for eluting the hydrocarbon components of the sample in the order of increasing boiling point. The column oven temperature is raised at a reproducible linear rate to effect separation of the hydrocarbons. Quantitation is achieved with a flame ionization detector. The sample retention times are compared with those of known hydrocarbon mixtures, and the cumulative corrected area of the sample determined to the 371°C (700°F) retention time is used to calculate the percentage of oil volatilized at 371°C (700°F). 

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