Open column sample application

In this mode of operation, the split valve is open throughout (Figure 2.70). In classical sample application, this mode of injection is suitable for concentrated solutions, through which the column loading can be adapted to its capacity and... 

Precolumn derivatization is often inadequate for dirty samples. In these cases, application of a postcolumn reaction detection system will often suffice. Deelder et al. (44) and van der Wal (45) have examined different configurations for postcolumn reactors and defined optimal selections on the basis of reaction time and type and effect on resolution and sensitivity. Both studies preferred the packed-bed reactor to the open tubular reactors when conventional column geometries were employed for separation, that is, 4.6 mm i.d. X 15 or 25 cm. 

Figure 3 Progress of frontal zone under application of pulsed electric field. A pulsed electric field was applied in 2-s cycles (electric field was applied for half of the period, and was stopped for the other half). Frontal zone positions were measured from the digital picture on a CRT. The perpendicular line shows the direction of movement of the frontal zone, and 1 mm in length is equal to 167 pixels. The horizontal line shows the time, and the minimum time scale observed is equal to one-fifteenth. A round open-tubular capillary column 75 pm in diameter and 28 mm in length was used. Applied voltage, 1 50 V. Colored sample methanol solution of 1 mM Rhodamine 6G.

Several types of surface modification have been employed [37,38] such as etching or deposition of very fine inert supports before application of the phase. The latter are referred to as support coated open tubular (SCOT) or by others as porous layer open tubular (PLOT) columns. They have a higher sample capacity than liquid coated columns due to the greater amount of phase per unit length. Several recent papers have described modified methods of column preparation [39-41] using Silanox 101 as the support. 

The open FFF channel is especially suited to fragile materials, and thermal FFF has found a definite niche in its application to ultrahigh-molecular-weight polymers. Furthermore, because samples need not be filtered, thermal FFF is the technique of choice for analyzing gels, rubbers, and other materials that tend to plug SEC columns [7]. Even particles can be analyzed... 

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