Gas chromatography columns used

Z. Fiu and J. B. Phillips, Farge-volume sample introduction into narrow-hore gas chromatography columns using thermal desorption modulation and signal averaging , /. Microcolumn Sep. 2 33-40 (1990). 

Z. Liu and J. B. Phillips, Sample introduction into a 5 pan i.d. capillary gas chromatography column using an on-column thermal desorption modulator , J. Microcolumn Sep. 1 159-162(1989). 

Gas Chromatography Column Use a stainless steel column, or equivalent, 3 m x 3.2 mm (od), packed with 10% Carbowax 20 M on 80/100-mesh Gas Chrom 2, or equivalent. After packing and before use, condition the column overnight at 200°, using a helium flow of 25 mL/min. 

Whole oil gas chromatography of the oil and condensate samples was performed using a Hewlett Packard 7673 Autosampler to inject 0.1 pi of whole oil spiked with internal standard into a split/splitless injector of a Hewlett Packard 5890 GC equipped with flame ionization detection. Products were swept into a 60 m J W Scientific DB-1 capillary gas chromatography column using helium as the carrier gas under constant flow conditions. The oven temperature program started at 30 °C, held for 5 min, ramped to 320 °C at 3°C/min, and held for 20 min. The injector was held at a constant 275 °C. 

Analytical and Test Methods. Gas chromatography is used for the quantitative analysis of malonates. Typical analysis conditions are 5% Reoplex 400 on Chromosorb G 80—100 mesh 2 m, 0.3 cm diameter metal column temperature for column = 120° C detector, 150°C and injector, 120°C. 

Deuterium exchange of conjugated enones and dienones on pretreated gas chromatography columns has been found useful for the characterization of these compounds by combined gas chromatography-mass spectrometry. ... 

Detectors. The function of the detector in HPLC is to monitor the mobile phase as it emerges from the column. The detection process in liquid chromatography has presented more problems than in gas chromatography there is, for example no equivalent to the universal flame ionisation detector of gas chromatography for use in liquid chromatography. Suitable detectors can be broadly divided into the following two classes ... 

Using the 3 mm. by 2 m. gas chromatography column described above, a mixture of stereoisomers of 2-allyl-5-methylcyclohexanone [Cyclohexanone, 5-methyl-2-(2-propenyl)-], prepared by allylation of the enamine of 3-methylcyclohexanone,7a showed peaks at retention times of 8.4 minutes (more stable isomer) and 9.6 minutes. A mixture of the two isomeric 2-allyl-3-methylcyclohexanones and the two isomeric 2-allyl-5-methylcyclohexanones clearly exhibited four distinct peaks on gas chromatography. 

The simplest analytical method is direct measurement of arsenic in volatile methylated arsenicals by atomic absorption [ 11 ]. A slightly more complicated system, but one that permits differentiation of the various forms of arsenic, uses reduction of the arsenic compounds to their respective arsines by treatment with sodium borohydride. The arsines are collected in a cold trap (liquid nitrogen), then vaporised separately by slow warming, and the arsenic is measured by monitoring the intensity of an arsenic spectral line, as produced by a direct current electrical discharge [1,12,13]. Essentially the same method was proposed by Talmi and Bostick [10] except that they collected the arsines in cold toluene (-5 °C), separated them on a gas chromatography column, and used a mass spectrometer as the detector. Their method had a sensitivity of 0.25 xg/l for water samples. 

In the commonly used pulse technique introduced by Kokes et al. C2), a spike of reagents is introduced into a carrier gas flowing over the catalyst and after that over a gas chromatography column which is used to determine the conversion of reagents to products. In this method, the concentrations of reagents in the catalyst bed are not defined, and kinetic measurements relating reaction rates to concentrations are impractical. 

Gas ionization detectors are widely used in radiochemistry and X-ray spectrometry. They are simple and robust in construction and may be employed as static or flow detectors. Flow studies have received attention in the interfacing of radioactive detectors with gas chromatographs. A radio-gas chromatograph (Figure 10.9) uses a gas flow proportional counter to monitor the effluent from the gas chromatography column. To achieve... 

Other combinations are available. For example, liquid chromatographs connected to mass spectrometers (known as liquid chromatography-mass spectrometry [LC-MS]) are fairly common. Almost any combination of two instruments that can be thought of has been built. In addition, two of the same instruments can be connected so that the output from one is fed directly into the other for further separation and analysis. Examples include two mass spectrometers in an MS-MS arrangement and two different gas chromatography columns connected in a series, known as GC-GC. To keep up with these advances, one needs to have a working knowledge of the fundamental principles involved in the techniques and of the abbreviations used for the various instrumentation methods. 

Capillary Column use in Purge and Trap Gas Chromatography II Use of the Model 1000 Capillary Interface, Tek/Data B021684, Tekmar Company, Cincinnati, Ohio. 

Gas chromatography makes use, as the stationary phase, a glass or metal column fdled either with a powdered adsorbent or a non-volatile liquid coated on a non-adsorbent powder. The mobile-phase consists of an inert-gas loaded with the vapourised mixture of solutes flowing through the stationary phase at a suitable temperature. In the course of the passage of the vapour of the sample through the column, separation of the components of the sample occurs in two ways, namely ... 

Gas chromatography analysis using a silicone gum column indicated the product to be 97% pure. 

The product may be analyzed by use of a gas chromatography column packed with either LAC-728 (diethylene glycol succinate) or Carbowax 20M suspended on Chromosorb P. Using a 2.5-m. LAC-728 column heated to 100°, the submitters found retention times of 9.4 and 13.0 minutes for cyclohexyl methyl ketone and cyclohexyldimethylcarbinol. Less than 1% of the carbinol by-product was present. 

Gas Chromatography Analysis of Water for Pesticides. All analyses for pesticides in water were done by gas chromatography. Solvents used for extraction were checked by gas chromatography for purity and interferences and all glassware used in the extraction was cleaned in a chromic acid/sulfuric acid mixture. Standards consisted of mixtures of various pesticides (actual commercial formulations) suspended or dissolved in water. These aqueous standards were extracted in the same manner as unknown solutions. The standard concentrations encompassed the concentration of unknowns to be determined. A standard curve normally consisted of a set of four pesticide concentrations. Blanks were run and an internal standard (eicosane) was used. The internal standard concentration was kept constant for all analyses. The conditions for GC analysis were guided by the pesticides expected in the water. For the more complex mixtures, such as those employed in the synthetic waste and those encountered in the field, a 6 ft., 3 percent SE-30 on GAS CHROM Q column sufficed. A typical chromatogram of a complex pesticide mixture is shown in Figure 2. ( )... 

On a 6-m. gas chromatography column packed with silicone gum. No. XE-60, suspended on Chromosorb P and heated to 240°, 2-benzyl-2-methylcyclohexanone (retention time 35.0 minutes) and 2-benzyl-6-inethvlcycl<)h( xanon(i (r< -tention time 33.2 tnimites, cis- and [Pg.24]

An example of a piece of equipment that would need to be validated is a new gas chromatography column that a vendor is touting as especially useful for the work. For the validation study, the column is installed in the instrument and the procedure is executed, perhaps repeatedly on all types of possible samples, so that the analyst can be certain that, again, the quality of the work meets expectations. 

Materials. The gases used (methane, ethane, ethylene, propane, propylene, n-butane, 2-methylpropane, and the butenes) were at least 99% pure (Cambrian Chemicals, Ltd.). The purity of each gas was tested by gas chromatography (columns of molecular sieve 5A, silica gel, or Porapak Q). 

Capillary gas chromatography (GC) using modified cyclodextrins as chiral stationary phases is the preferred method for the separation of volatile enantiomers. Fused-silica capillary columns coated with several alkyl or aryl a-cyclo-dextrin, -cyclodextrin and y-cyclodextrin derivatives are suitable to separate most of the volatile chiral compounds. Multidimensional GC (MDGC)-mass spectrometry (MS) allows the separation of essential oil components on an achiral normal phase column and through heart-cutting techniques, the separated components are led to a chiral column for enantiomeric separation. The mass detector ensures the correct identification of the separated components [73]. Preparative chiral GC is suitable for the isolation of enantiomers [5, 73]. 

The aroma of foods is caused by volatile compounds which are perceived by the human nose. Many studies (reviews in [1, 2]) have indicated that only a small fraction of the hundreds of volatiles occurring in a food sample contribute to its aroma. To detect these compounds, a method proposed by Fuller et al. [3] is used. In this procedure, which is designated gas chromatography-olfactometry (GC-O), the effluent from a gas chromatography column is sniffed by an expert who marks in the chromatogram each position at which an odour impression is perceived. 

Different capillary columns are available for organic acid separation and analysis. In our laboratory, the gas chromatography column in all GC-MS applications is crosslinked 5% phenyl (poly)methyl silicone, 25 m internal diameter 0.20 mm stationary phase film thickness 0.33 pm (Agilent HP-5, DB-5, or equivalent). Several instrument configurations are commercially available, which allow for positive identification of compounds by their mass spectra obtained in the electron impact ionization mode. A commercially available bench-top GC-MS system with autosampler (Agilent 6890/5973, or equivalent) is suitable. Software for data analysis is available and recommended. The use of a computer library of mass spectra for comparison and visualization of the printed spectra is required for definitive identification and interpretation of each patient specimen. 

Historically, silica gel, which is thermally stable and insensitive to oxygen, was one of the first compounds used as a stationary phase for gas chromatography columns. Today, solid phases are made with more elaborate materials. The efficiency of graphite-based columns is very high (see Fig. 2.9 below). 

Materials. Cyclohexene, obtained by dehydration of reagent grade cyclohexanol (3), was heated at reflux over sodium metal, fractionated on a 60-cm. Helix packed column, stored over sodium, and filtered just before use. No impurity was found by gas chromatography (column, TCP and Si-550 carrier gas, helium). Propylene (Neriki Research Grade) used showed no impurity by gas chromatography (column, active carbon and acetonylacetone). 

Selected ion monitoring mass chromatogram showing caffeine and caffeine-D3 eluted from a capillary gas chromatography column. [From D. W. Hill, B. T. McSharry, and L. S. Trzupek, Quantitative Analysis by Isotopic Dilution Using Mass Spectrometry." J. Chem. Ed. 1988, 65, 907.]... 

In the early days of HPLC (1970-78), solid supports were coated with a liquid stationary phase as in gas chromatography. Columns with these packings had short lifetimes and a gradual decrease in resolution because there was continuous loss of the liquid stationary phase with use of the column. 

Gas chromatography is used to analyze volatile derivatives of amino acids. Phenylthiohydantoins (products of Edman degradation) may be analyzed directly by GC but are better resolved if converted to their trimethylsilyl derivatives with N, O-bis(trimethylsilyl) acetamide. Free amino acids are generally converted to their 7V-trifluoroacetyl- -butyl esters or trimethylsilyl derivatives before GC analysis. For best results, all gas chromatography of amino acid derivatives should be done with a glass column and injection port, as contact with metals causes extensive decomposition of the derivatives. 

---