CHROMATOGRAPHY SPECIALISTS SPECIFY ALLTECH
Figure 10. Chromatogram of a C^Cg hydrocarbon mixture (alkanes, alkenes, cycloalkanes, and aromatics) on a SCOT column (from the publication of Ettre, Purcell, andBilleb, 1966 [50]) 100-ft X 0.50-mm i.d. SCOT column, prepared with squalane liquid phase; phase ratio: 67. Flame ioniza tion detector. The first five peaks: 1 = methane, 2 = ethane, 3 = propene, 4 = propane, 5 = 2-methylpropane. Courtesy of Marcel Dekker, Inc., New York, N.Y.
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Figure 11. Chromatogram of an oil of marjoram sample obtained in a GC/MS system using a SCOT column (from the investigations of Averill and Struck, 1966; see Ref erence 49) 50-ft X 0.50-mm i.d. SCOT column, prepared with OS-138 polyphenyl ether liquid phase. Phase ratio: 50. Temperature: programmed, as given. Total ion current recording
duce the activity of the inside tube surface. Thus, conscious variation of the liquid-phase film thickness was not plausible until the advent of glass columns. According to the theory of open-tu bular columns, columns prepared with a thin film have a higher absolute effi ciency. This was the primary reason why most of the glass columns were prepared with a relatively thin (about 0.2-μΐη) film. However, it had been understood for a long time that it is advantageous to select the film thick ness according to the type of sample: This had been pointed out as early as 1961-63 by Jentzsch and Hôvermann (27,28). In 1974 in our laboratories, Averill and March (40) illustrated the differences in the separation of early peaks in complex natural samples, such as gasolines and essential oils, when
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changing the film thickness from 0.25 μΐη to 0.50 μπι; in fact, columns with a 0.50-μπι film (in addition to 0.25μΐη film columns) were commercially introduced at that time. Continuing these investigations, in 1979 Johansen (41) published his pioneering study on the characteristics of 0.27-mm i.d. col umns coated with l-μΐη film. The introduction of immobilized phases finally permitted the prepara tion of open-tubular columns with film thicknesses well above 1 μιη. The first detailed reports on such columns, with film thicknesses up to 8 μπα., were published in 1983 almost simulta neously by the Grobs (42), Sandra (43), and ourselves (44,45). Such col umns, particularly with the simulta neous increase of the tube diameter, represent an exciting new field in the application of open-tubular columns. Although this discussion dealt only
