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CHROMATOGRAPHY SPECIALISTS SPECIFY
ALLTECH
You're a specialist, and so are we. It takes a specialist to keep up with the changes and advancements in the field, and it takes a specialist to pioneer those changes. Alltech does both. For 30 years, Alltech Associates, Inc. /Appl ied Science Labs has been the l e a d e r in i n n o v a t i v e chromatography products. Our Gas Chrom Q is an industry standard; we pioneered the use of Vespel ferrules; we developed the Microbore HPLC column; and our new NON-PAKD GC columns are fast replacing Packed GC columns in labs around the world; and on and on and on; product af ter p r o d u c t , innovation after innovation.
It takes a specialist to understand what another specialist needs, both now, and in the future. At Alltech, we understand. For your free copy of our catalog, please contact us at:
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Figure 10. Chromatogram of a C^Cg hydrocarbon mixture (alkanes, alkenes, cy-cloalkanes, 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 ionization detector. The first five peaks: 1 = methane, 2 = ethane, 3 = propene, 4 = propane, 5 = 2-methyl-propane. Courtesy of Marcel Dekker, Inc., New York, N.Y.
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 Reference 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-tubular columns, columns prepared with a thin film have a higher absolute efficiency. 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 thickness 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
changing the film thickness from 0.25 μΐη to 0.50 μπι; in fact, columns with a 0.50-μπι film (in addition to 0.25-μΐη 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. columns coated with l-μΐη film.
The introduction of immobilized phases finally permitted the preparation 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 simultaneously by the Grobs (42), Sandra (43), and ourselves (44,45). Such columns, particularly with the simultaneous increase of the tube diameter, represent an exciting new field in the application of open-tubular columns.
Although this discussion dealt only
1430 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985
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