Open tubular columns chemically bonded

The Liquid Phase. The stationary phase in an open tubular column is generally coated or chemically bonded to the wall of the capillary column in the same way the phase is attached to the support of a packed column. These are called nonbonded and bonded phases, respectively. In capillary columns there is no support material or column packing. 

Although open tubular columns have been used for RPLC,42 most applications use packed columns. The most widely used column packings are formed by chemically bonding butyl (C4), octyl (C8), or octadecyl (C18) chains to a silica surface. Phenyl (Ph), cyano (CN), and amino (NH2) functionalities are also used. Polymeric packings which are finding broad acceptance include alkyl-grafted poly(methylmethacrylate) and alkyl-grafted or unmodified... 

The chromatographic column used was a wall-coated, open tubular column (WCOT) (J W Scientific) with a DB-1 Durabond chemically bonded stationary phase that had a nominal film thickness of 0.25 pm. The column was 60 m long X 0.32 mm i.d. The DB-1 stationary phase has chromatographic properties similar to SE-30. 

Programmed temperature (120 -200°C) chiral separation on a 0.25-mm x 25-m open tubular column with a 0.25-nm-thick stationary phase containing 10 wt% fully methylated p-cyclodextrin chemically bonded to dimethyl polysiloxane. [From W. Vetter and W. Jun, Elucidation of a Polychlorinated Bipyrrole Structure Using Enantioselective GC," Anal. Chem. 3002, 74,4287.]... 

Hydrocarbons containing two and three carbons are generally separated on packed columns. Chemically bonded materials such as n-octane or phenyl isocyanate on Porasil have proven to be good separator systems for these highly volatile nonmethane hydrocarbons. However, these systems require a separate analysis from that employed for the C4-C12 hydrocarbons (7). Recent developments include the use of capillary-type columns [e.g., Al203 porous layer open tubular (PLOT)] for separation of the lower molecular weight hydrocarbons (8). 

Because of unfavorable mass transfer properties in liquids, highly efficient separations and short separation times potentially available for open tubular columns can be realized only in columns of small internal diameter (< 25 xm) [309]. These columns have very low phase ratios and serious detection problems arise. Several methods have been proposed to Increase the surface area, and hence the stationary phase capacity, by chemical etching of the interior wall [335] or by adhesion of a thin porous silica or polymer layer to the wall [336-338]. The sol-gel process allows an increase in surface area and formation of a retentive chemically bonded phase in a single step. None of these processes, however, adequately address the problems of low retention, low sample capacity, poor sample detectability, and unfavorable handling characteristics that prevent wider use of open tubular columns in capillary electrochromatography. 

Jorgenson, J.W. Guthrie, E.J. Liquid chromatography in open-tubular columns Theory of column optimization with limited pressure and analysis time, and fabrication of chemically bonded reversed-phase columns on etched borosilicate glass capillaries. J. Chromatogr. 1983, 255, 335-348. 

Figure 15. Open tubular liquid chromatography of amine-NBD derivatives using on-column fluorescence detection. Peaks correspond from left to right to ethylamine, n-propylamine, n-butylamine, cyclohexylamine, and n-hexylamine. Conditions 20-p.m X 8.3-m column with C-18 bonded phase 20% acetonitrile and 80% water (v/v) mobile phase at a linear velocity of 0.50 cm/s on-column injection of 5 nL. (Reproduced from reference 59. Copyright 1984 American Chemical Society.)...

Gas Chromatography. The basic components of a gas chromatograph are a carrier gas system, a column, a column oven, a sample injector, and a detector. Very pure helium is the near-universal carrier gas for environmental and many other analyses. Open tubular GC columns are constructed of fused silica with low-bleed stationary phases of varying polarity chemically bonded to the silica surface. Columns are typically 30-75 m in length and have inside diameters (ID) in the range of about 0.25-0.75 mm. The column oven is capable of precise temperature control and temperature programming at variable rates for variable times. 

In gais chromatography (GC), open-tubular caplllaury columns cam produce much more theoretical plate numbers tham conventional packed columns. Open-tubular capillary columns have been examined am separation tools also in liquid chromatography(LC)(8-12). Coated columns, ca. 20 m X 10-30 vim l.d., produced theoretical plate numbers in excess of 100,000 but long-term stability of these columns was scxnewhat poor even if the mobile phame is saturated with the mobile phase. Accordingly chemically bonded or immobilized stationaury phatses should be preferred. 

This paper describes the performance of micro padced fused-silica columns and chemically bonded octadecylsilane(ODS) open-tubular capillary columns. 

Micro packed fused-silica columns showed high resolution by resolving a lot of components of complex mixtures. Solutes with wide poleurity were sepeirated on high-resolution micro packed fused-silica columns with the help of gradient elution. Chemically bonded open-tubular capillary columns with 31 ym i.d. could resolve epoxy resin oligomers although their performance was somewhat poorer than that of packed columns. 

Gas chromatography columns for interplanetary exploration should be very efficient, due to the stringent demands imposed on payload. Porous-layer open tubular (PLOT) columns loaded with a styrene-divinyl benzene copolymer showed better performance than Cromosorb 103 or Porapak Q columns in the analysis of low molecular weight hydrocarbons and nitriles. Potassium chloride-deactivated alumina PLOT columns, on the other hand, were not good for the intended purpose, because low molecular weight nitriles were difficult to elute. Wall coated open tubular (WCOT) columns with a stationary chemically bonded phase of dimethyl siloxane have the mechanical resilience to endure the conditions of extraterrestrial exploration and separated efficiently C1-C4 nitriles. Permanent gases were analysed in the presence of hydrocarbons and nitriles with a PLOT capillary column. The equilibrium constant for the interaction of nitrile groups with various solutes was determined by GLC. ... 

For open tubular (OT) or capillary columns, the liquid is coated on the inside of the capillary. To make it adhere better, the liquid phase is often extensively cross-linked and sometimes chemically bonded to the fused silica surface. See Chapter 6 for further details. 

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