GC capillary column

Giddings [2] estimated that, for a well-packed column, (y) takes a value of about 0.6. Equation (11) accurately describes longitudinal dispersion in GC capillary columns and equation (12) accurately describes longitudinal dispersion in GC and LC packed columns. Experimental support for these equations will be given in a later chapter. 

The value of (q) takes into account the precise shape of the pool of stationary phase for a uniform liquid film as in a GC capillary column, q = 2/3. Diffusion in rod shaped and sphere shaped bodies (e.g., paper chromatography and LC) gives q=l/2 and 2/15, respectively [2]. 

The standard deviation of the extra-column dispersion is given as opposed to the variance because, as it represents one-quarter of the peak width, it is easier to visualize from a practical point of view. It is seen the values vary widely with the type of column that is used, (ag) values for GC capillary columns range from about 12 pi for a relatively short, wide, macrobore column to 1.1 pi for a long, narrow, high efficiency column. 

The packed GC column has a value for (og) of about 55 pi, whereas the high efficiency microbore LC column only 0.23 pi. It is clear that problems of extracolumn dispersion with packed GC columns are not very severe. However, shorter GC capillary columns with small diameters will have a very poor tolerance to extracolumn dispersion. In the same way, short microbore LC columns packed with small... 

It is for this reason that not only the various Sulfur-containing groups present, but also the mono- and dimethyl-substituted species of benzothiophenes and dibenzoth-iophenes have to be separated and quantified individually. As the number of sulfur compounds present in (heavy) middle distillate fractions may easily exceed 10 000 species, a single high resolution GC capillary column is unable to perform such a separation. 

The use of SPE with porous materials such as alumina, diatomaceous earth, Horisil and silica for the cleanup of fat-soluble organochlorine pesticides in fatty foods such as meat, flsh, shellfish, milk and vegetable oils has been well documented. The choice of elution solvents is critical because relatively small amounts of lipid in the final extract can cause rapid deterioration of GC capillary columns and also contaminate the gas chromatograph. A number of workers have used a porous material in tandem with Cig to effect an improved cleanup.Di Mucchio employed a multicartridge system comprising Extrelut, silica and Cig to extract organophosphorus pesticides from oils and fatty extracts. Relatively few literature applications include the pyrethroids, but Ramesh and Balasubramanian reported a simple carbon-based SPE method for the analysis of pyrethroids in vegetable oil. 

MaStovska et al5 demonstrated the use of a 5-m GC capillary column surrounded by a tube of resistively heated steel to raise the column temperature more rapidly and uniformly than a conventional GC oven. They analyzed 15 organophosphoms... 

Numerous types of GC injectors have been manufactured over the past four decades. The most commonly used injection techniques have been reviewed and described by Grob, who correctly states that analysts must fully understand the techniques before they can make the most appropriate choice for their particular application(s). For most GC capillary column applications, the split/splitless, programmed-temperature vaporization (PTV) and on-column injectors remain the most popular. However, over the last few years, technology has progressed rapidly to provide injectors that allow more of the sample extract on to the GC column without overloading it. 

Chlorinated Hydrocarbons by GC Capillary Column Technique 8131 Aniline and Selected Derivatives by GC... 

FIGURE 17.1 (iJ)-Af,Af,Af-trimethyl-2-aminobutanol-bis(trifluoromethane-sulfon)imidate as tbe cbiral additive. (A) CE BGE Na-pbospbate buffer pH 6.0 and lOmM ionic liquid, analyte propranolol. (B) HPLC, mobile phase H2O acetonitrile (AcN) (6 4) with 10 mM ionic liquid, analyte 2,2 -diamino-l,l -binafthalene. (C) GC capillary column coated with the chiral ionic liquid, analyte citronella. (Reprinted with permission from Anal. Lett., 39, 1447, 2006. Copyright 2006, Taylor Francis.)... 

Researchers have coupled two GC capillary columns with different lengths and polarities in series to optimize separation of complex mixtures of volatile organics in air samples (Clair et al. 1991). 

This was solved by use of a jet separator where the column effluent was passed across a very narrow gap between two jets and the highly diffusable carrier gas was largely removed, whereas the heavier analyte molecules crossed the gap without being vented. The problem of removing the carrier gas no longer exists since GC capillary columns provide a flow rate of 0.5-2 ml/min, which can be directly introduced into the mass spectrometer without it losing vacuum. 

This type of injector is used in conjuction with capillary column GC. Capillary columns commonly have internal diameters beteen 0.2 and 0.5 mm and lengths between 12 and 50 m. Injection takes place into a heated glass or quartz liner rather than directly onto the column. 

Consider a GC capillary column where the length, diameter and thickness of the film of the stationary phase could all be modified (one factor at a time and without adjustment of the apparatus physical characteristics, such as temperature and pressure, yet maintaining a flow such that the linear velocity of the gas remains the same). 

After the three solvent extractions, 50 mL of wet resin from each method was placed in separate columns and eluted three times with 1 bed volume of methylene chloride a 20-min contact time between elutions was used. The third elution was collected and concentrated to 1 mL. A homologous series of normal hydrocarbons from C7 to C26 were added as internal standards. Two and one-half microliters of each concentrate was injected onto a 60-m X 0.32-mm i.d., DB-1 fused-silica GC capillary column (J W Scientific). 

A method for determination of cholesterol oxidation products in milk powder and infant formulas is presented. Provides useful information on resolution of cholesterol oxidizing products from unoxidized cholesterol on a GC capillary column. 

Perkin Elmer HS-6 headspace sampler or equivalent 30-m x 0.32-mm i.d. x LO-pm film thickness DB-5 GC capillary column or equivalent Helium... 

This procedure allows the differentiation of odor active compounds from odorless substances within a complex mixture of volatiles. For decades this procedure has been successfully applied for aroma analyses of foods (Grosch, 1993). The mixture of volatile compounds either collected in a purified organic solvent extract or in a defined headspace volume is separated into its different components by means of GC and the effluent gas flow at the end of the GC capillary column is split between a FID and an experienced test person s nose. By sniffing the column effluent, the human nose is able to perceive the odor active compounds contained in a complex mixture and the test person can mark the corresponding spot in the FID chromatogram recorded in parallel and attribute a certain odor quality. A sample GC—O chromatogram of a solvent extracted material is shown in Figure 8.7. 

Naikwadi KP, Karasek FW. 1990a. Development of GC capillary column for isomer-specific separation of toxic isomer of PCCDs and PCDFs in environmental samples. Chemosphere 20 1379-1384. 

G. Alexander, Z. Juvancz, et al., Cyclodextrins and their derivatives as stationary phases in GC capillary columns, HRC CC J. High Res. Chromatogr. Chromatogr. Commun., 77 110-113 (1988). 

Monyl phenyl) acetic acid, octylphenol polyoxyethylate, C2-C4 diols, fatty acids Capillary column GC Capillary column GC-MS [90- 94]... 

NJ). Two microliters of the respective samples were injected (the solvent was vented) into a 50 m x 0.32 mm OV-1 methyl silicone GC capillary column. The GC was programmed from an initial temperature... 

To clarify the role of B-carotene to the aroma of roasted green tea, B-carotene was heated in a pyrolyzer at 180°C for 6 minutes. The reaction was carried out under air with and without catechin gallates, a component of tea leaves. The volatile products were trapped in a precolumn cooled by dry ice/acetone. The precolumn was then connected to a GC capillary column and the volatiles then analyzed by GC-MS. 

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