Capillary columns analysis time

A more complex sample containing many more (at least five times as many) components can be separated on a capillary column than in an equivalent packed column analysis time alternatively longer analysis times can be used to obtain the maximum separating capability for complex samples. 

Gas chromatography is not an identification method the components must be identified after their separation by capillary column. This is done by coupling to the column a mass spectrometer by which the components can be identified with the aid of spectra libraries. However tbe analysis takes a long time (a gasoline contains aboutTwo hundred components) so it is not practical to repeat it regularly. Furthermore, analysts have developed te hpiques for identifying... 

Time, Cost, and Equipment Analysis time can vary from several minutes for samples containing only a few constituents to more than an hour for more complex samples. Preliminary sample preparation may substantially increase the analysis time. Instrumentation for gas chromatography ranges in price from inexpensive (a few thousand dollars) to expensive (more than 50,000). The more expensive models are equipped for capillary columns and include a variety of injection options and more sophisticated detectors, such as a mass spectrometer. Packed columns typically cost 50- 200, and the cost of a capillary column is typically 200- 1000. 

Although the OTHdC has several unique applications in polymer analysis, this technique has several limitations. First, it requires the instrumentation of capillary HPLC, especially the injector and detector, which is not as popular as packed column chromatography at this time. Second, as discussed previously, the separation range of a uniform capillary column is rather narrow. Third, it is difficult to couple capillary columns with different sizes together as SEC columns. 

The products were identified by comparing the retention times of the reaction products with commercial compounds, and by GC-MS analysis in a Hewlett-Packard 5973/6890 GC equipped with an electron impact ionization at 70 eV detector and a cross-linked 5% PH ME siloxane (0.25 mm coating) capillary column. The reaction products were separated from the catalyst with filter syringes and analyzed in an Agilent 4890D and a Varian 3400 GC equipped with a flame ionization detector, and CP-Sil 8CB (30 m x 0.53 mm x 1.5 pm) and DB-1 (50 m x 0.52 mm x 1.2 pm) columns, respectively. Decane was used as an internal standard. The catalyst was thoroughly washed after reaction with acetonitrile, acetone and water, and dried overnight under vacuum at 40°C. 

GC-MS analysis is schematically indicated in Figure 7.13. In GC-MS data collection, account should be taken of the fact that GC peaks eluting from a capillary column are only a few seconds wide, which imposes fast scan times. As most compounds analysed by GC-MS are low-MW (<800 Da), a relatively short... 

Mclnnis and Dobbs179 showed that both a DB-5 megabore capillary-GC column and a packed (20% SP2100 on 60-80 mesh Supelcoport) GC column could be used for the analysis of C-14 labelled chlorotrimethylplumbane. Analysis times using the DB-5 megabore column were approximately one-half those required on the packed column. 

The analysis of estrogens and progestogens by GC-MS has been carried out with a variety of capillary columns using helium as carrier gas [7,26,36,43, 59, 66]. LODs in the range of 0.1—1.8 ng L 1 have been achieved. In terms of sensitivity, GC- and HPLC-tandem mass spectrometry are comparable techniques. However, the derivatization carried out prior to GC separation is time consuming and can be a source of inaccuracy [7]. 

In order to perform qualitative and quantitative analysis of the column effluent, a detector is required. Since the column effluent is often very low mass (ng) and is moving at high velocity (50-100 cm/s for capillary columns), the detector must be highly sensitive and have a fast response time. In the development of GC, these requirements meant that detectors were custom-built they are not generally used in other analytical instruments, except for spectroscopic detectors such as mass and infrared spectrometry. The most common detectors are flame ionization, which is sensitive to carbon-containing compounds and thermal conductivity which is universal. Among spectroscopic detectors, mass spectrometry is by far the most common. 

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