Operating chromatographic column

Tiselius [3] defined three distinct modes in which a chromatographic column can be operated, elution, displacement and frontal. In addition to this there are ways of operating chromatographic columns which can be considered as intermediate between these modes and, in addition, there are various techniques which have been applied to chromatographic separations in order to improve throughput. These will be discussed in this Section. 

As described above, the mobile phase carrying mixture components along a gas chromatographic column is a gas, usually nitrogen or helium. This gas flows at or near atmospheric pressure at a rate generally about 0,5 to 3.0 ml/min and evenmally flows out of the end of the capillary column into the ion source of the mass spectrometer. The ion sources in GC/MS systems normally operate at about 10 mbar for electron ionization to about 10 mbar for chemical ionization. This large pressure... 

An ion beam can be produced from a number of different sources, but for this instmment — used for biochemical examination of thermally unstable, large molecules — an atmospheric-pressure inlet such as APCl or ES would generally be used. These can be operated with liquid inlets from chromatographic columns or simply from static solutions. 

Each of the PLgel individual pore sizes is produced hy suspension polymerization, which yields a fairly diverse range of particle sizes. For optimum performance in a chromatographic column the particle size distribution of the beads should be narrow this is achieved by air classification after the cross-linked beads have been washed and dried thoroughly. Similarly, for consistent column performance, the particle size distribution is critical and is another quality control aspect where both the median particle size and the width of the distribution are specified. The efficiency of the packed column is extremely sensitive to the median particle size, as predicted by the van Deemter equation (4), whereas the width of the particle size distribution can affect column operating pressure and packed bed stability. 

A six-port valve was first used to interface the SEC microcolumn to the CZE capillary in a valve-loop design. UV-VIS detection was employed in this experiment. The overall run time was 2 h, with the CZE runs requiring 9 min. As in the reverse phase HPLC-CZE technique, runs were overlapped in the second dimension to reduce the apparent run time. The main disadvantage of this yu-SEC-CZE method was the valve that was used for interfacing. The six-port valve contributed a substantial extracolumn volume, and required a fixed volume of 900 nL of effluent from the chromatographic column for each CZE run. The large fixed volume imposed restrictions on the operating conditions of both of the separation methods. Specifically, to fill the 900 nL volume, the SEC flow rate had to be far above the optimum level and therefore the SEC efficiency was decreased (22). 

Reaction vessel. Use a small tube or vial fitted with a Teflon-lined screw cap. Gas chromatograph. Operate the column isothermally at 210 °C using a flame ionisation detector. 

Unrecognized shifts in the calibration of the columns will affect the raw data, which are in terms of elution time of the components of the specimen from the chromatographic columns. Use of log hydrodynamic volume allows the operator to correct for such... 

The 1/16" x 0.02" i.d. transfer line also functioned as a sample dilution device in other applications, a stainless steel column packed with glass beads has been found to be useful for dilution. This simple dynamic dilution technique has been used extensively in flow injection analysis.3 A refractive index detector is typically used to measure the sample transfer time. As shown in Figure 4, approximately 5 minutes is required to transfer the sample plug to the Rheodyne valve. As the apex of the sample band passes though the Rheodyne valve, the valve is activated and 1 pi injected onto the liquid chromatographic column. The sample transfer time was checked periodically over 1 year of operation and found to be stable. 

As with most aspects of downstream processing, the operation of chromatographic systems is highly automated and is usually computer controlled. Whereas medium-sized process-scale chromatographic columns (e.g. 5-151 capacity) are manufactured from toughened glass or plastic, larger... 

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