PLOT column

Heijmans, H., de Zeeuw, J., Buyten, J., Peene, J., and Mohnke, M. PLOT columns. American Laboratory, August, 28C, 1994. 

Fused silica capillary columns of various internal bores and of lengths in the range 25 to 50 m are mainly employed for analytical separations. A variety of polar and non-polar column types are available including those open tubular types with simple wall coatings (WCOT), those with coatings dispersed on porous solid-supports to increase adsorbent surface area (SCOT) and porous layer open tubular (PLOT) columns. Important stationary phases include polyethylene glycol, dimethylpolysiloxane and different siloxane copolymers. Various sample introduction procedures are employed including ... 

Suitable PLOT columns for the determination of vinyl chloride monomer in PVC include 15.00 m, 0.53 mm bonded polystyrene-divinyl benzene and 30 m, 0.53 mm porous divinyl benzene homopolymer types. Typical responses for vinyl chloride monomer standards (0.06, 0.19 and 0.31 mg/1) in N,N-d imethylaceta-mide expressed as mg/kg vinyl chloride (PVC sample) using the 30 m homopolymer column and flame ionisation detection are shown in Figure 38. An automatic static headspace sampler was employed. 

Porous layer open tubular (PLOT) columns, 4 615 6 379... 

Several approaches towards monolithic GC columns based on open pore foams prepared in large diameter glass tubes were reported in the early 1970s [26,27, 110]. However, these columns had poor efficiencies, and the foams possessed only limited sample capacities in the gas-solid GC mode. Subsequent experiments with polymerized polymer layer open tubular (PLOT) columns where the capillary had completely been filled with the polymer were assumed to be failures since the resulting stationary phase did not allow the gaseous mobile phase to flow [111]. 

These have now been superseded by capillary columns, which offer greatly improved separation efficiency. Fused silica capillary tubes are used which have internal diameters ranging from 0.1 mm (small bore) to 0.53 mm (large bore) with typical lengths in excess of 20 m. The wall-coated open tubular (WCOT) columns have the internal surface of the tube coated with the liquid (stationary) phase and no particulate supporting medium is required. An alternative form of column is the porous-layer open tubular (PLOT) column, which has an internal coating of an adsorbent such as alumina (aluminium oxide) and various coatings. Microlitre sample volumes are used with these capillary columns and the injection port usually incorporates a stream splitter. 

Guess Second-Order Kinetics. Equation 16 tells that 1/C vs. t should give a straight line. So calculate column 4, plot column 1 vs. column 4, as shown in Fig. E3.16. Again, this does not give a straight line, so a second-order kinetic form is rejected. 

Figure 2.9—Gas analysis. On the left is one of the first chromatograms ever obtained, point by point, representing a mixture of air, ethylene and acetylene separated on silica gel (E. Cremer and F. Prior, Z. Elektrochem. 1951, 55, 66). On the right is a gas analysis obtained on a PLOT column (reproduced by permission of Supelco).

PLOT Columns. Porous-layer open tubular columns wherein the internal wall is coated with a layer of adsorbent support. If the support is then coated with a liquid phase it is referred to as a SCOT Column (i.e., support-coated open tubular column). 

Capillary columns coated with aluminum oxide and molecular sieves can be described as absorption phases [22]. These columns are also known as porous-layer open tubular (PLOT) columns. Aluminum oxide PLOT columns deactivated with potassium chloride have been very effective at the separation of C,.,0 hydrocarbons. 

Fig. 6.18. Electrochromatogram of four basic proteins obtained by isocratic separation using a modified polychloromethylstyrene-based PLOT column (Reprinted with permission from [50]. Copyright 1999 Elsevier). Column 47 cm (active length 40 cm) x 20 pm, inner polymer layer 2 pm mobile phase 20% acetonitrile in 20 mmol/1 phosphate buffer pH 2.5 voltage -30 kV EOF velocity measured with dimethylsulfoxide (DMSO) -3.46 x 10"8 m2V ls 1, migration time for DMSO 3.10 min. Peaks a-chymotrypsinogen (1), ribonuclease (2), lysozyme (3), cytochrome C (4).

For a period of time, OT columns that had characteristics intermediate between those of WCOT and packed columns were popular. There were two types, but they were similar. Support coated open tubular (SCOT) columns had a thin layer of solid support coated on the inside wall of a capillary tube of larger diameter than that used for WCOT columns. This layer was coated with stationary liquid similar to packed columns. Porous layer open tubular (PLOT) columns were similar but made differently for example, the solid support was added while the capillary tube was being drawn. With a few exceptions, SCOT and PLOT columns are no longer popular because wide diameter WCOT fused silica columns are as good, more stable (no layer to flake off), and easier to use. Subsequent discussion will be restricted to WCOT columns. 

Porous layer open tubular (PLOT) columns were used to separate basic proteins and peptides [15]. The use of these types of columns was prompted by their high permeability and by the relatively high loading capacity due to an increased surface area by the porous layer. The authors showed that under conditions of reversed-phase chromatography at acidic pH, the EOF mobility was over 8-fold higher than that in raw fused-silica capillary, which is an indication of the high surface charge present in the porous layer. As expected, the EOF... 

The concentrations of hydrocarbon at the inlet and outlet of the reactor were measured using FTIR (Nicolet) with a meicury-calcium-telluride (MCT) detector, which was cooled by liquid nitrogen and gas cell (Infrared Analysis), and with 16 scans and a resolution of 2 cm. The concentrations were also checked using GC (HP3890plus) with FID (flame ionization detector) and HP plot column. The vapor pressures of the hydrocarbons were calculated by using Reid equation [6]. 

Also important is the use of the modem chromatographic methods to separate and identify individual components in commercial cmde shale oil. The use of efficient gas chromatographic columns coupled with ancillary techniques such as mass spectrometry and vapor-phase IR spectroscopy allows the identification of individual shale oil components. A principal part of this study is the comparison of diflFerent types of open tubular columns for the separation of the alkane-alkene fraction of shale oil WCOT, SCOT, and PLOT columns are examined. Gas chromatographic separation of shale oil acids and bases also is performed allowing the identification of these components. The potential utility of subtractive pre-columns in HPLC analysis is illustrated also. 

---