Column end terminators

The first column of Table 7-1 lists all values of m. Since m = mx + m2, and the maximum of this sum is + j2, this is the largest permitted m. To each choice of m (between jx + j2 and —jx — j2) correspond several l>j1ml lti2m2 functions and an equal number of A,m functions. The values of mx and m2 in terms ofjx and j2 are given in the second column, those of j and m in the third. How many functions will there be altogether This depends on how far the table can be carried downward. Now the second column terminates when either mx reaches the value —jx, or when m2 reaches the value —j2, whichever happens first. Hence the third column ends when j reaches the value jx +j2 - 2 min (jx or j2) = 1 - j21. For everjj there are 2j + 1... 

In order to obtain a perfect junction between the column end and the terminator, one must ensure that the column ends are perfectly flat. 

Sample Distribndon All HPLC columns are terminated by filter assemblies, which often have incorporated some means to ensure that the sample is distributed uniformly over the cross section of the column. The proper functioning of these devices can be impaired by blockage. If this is the case, the sample band at the column top is distorted, which can result in a reduced column performance. The phenomenon is indistinguishable from a collapsed bed all peaks exhibit a similarly distorted profile independent of the retention (Fig. 17.6). Open the column and inspect the filter and the packed bed. If the packed bed appears intact, it is worthwhile to try to clean the filter assembly or replace it with a new one. But the appearance of an undisturbed bed does not guarantee that the column has not collapsed. Often, a bed collapse has occurred somewhere in the middle of the packed bed and is not visible at the ends. 

Install the column in the chromatographic oven and connect one column end to the sample inlet system. Turn on the source of carrier gas and set the flow controller (or pressure regulator) to the flow rate to be used in the analyas. Increase the column temperature to the maximum value to be used in the analysis and maintain this temperature for 30 min. Cool the column temperature to room temperature and connect the remaining column end to the detector. Care must be taken that the column terminates as close as possible to the tip of the FID jet. The temperature of the column between the column oven and the detector jet must be maintained above the maximum column temperature. 

Two forms of interface have been commercially developed [7] which allow analytes in a flowing liquid stream - it has to be pointed out, not necessarily from an HPLC system (see below) - to be ionized by using FAB. These are essentially identical except for that part where the HPLC eluate is bombarded with the heavy-atom/ion beam. Both of these interfaces consist of a probe in the centre of which is a capillary which takes the flowing HPLC eluate. In the continuous-flow FAB interface (Figure 4.3), the column eluate emerges from the end of the capillary and spreads over the probe tip, while in the frit-FAB interface the capillary terminates in a porous frit onto which the atom/ion beam is directed. 

The packing material, used for the LEG work was Controlled-Pore Glass (CPG) from Electronucleonics, Fairfield, N.J. with various pore diameters similar to those used by others (6,2 ) (500-10,000 A). Each k.6 mm I.D. x 100 cm column was dry packed with the CPG of a specific pore size by tapping and vibration until a terminal, bed volume was reached. Stainless steel 20-ym frits were used on each end of the column along with the appropriate low-dead volume end-fittings. 

N.M. Junk in 4thONRSympDeton (1965), pp 92-101. Observations made in a water medium show that for several expls at various diams, the lateral pressure is 38 to 73% of the shock pressure generated at the terminal end of the explosive column... 

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