Cooling the column

The process of concentrating volatile solutes by cooling the column s inlet below room temperature. 

The injector temperature should be determined by the nature of the sample and the volume injected, not by the column temperature. When analyzing biological or high-boiling samples, clean the injector body with methanol or other suitable solvent once per week. Install a clean packed injector liner and a new septum, preferably near the end of a workday. Program the column to its maximum temperature, then cool the column and run a test mixture to check the system using standard conditions. 

In capillary column gas chromatography, it is often required to raise and lower the column temperature very rapidly and to raise the sample injection port temperature. In one design of gas chromatography, the Shimadzu GC 14-A, the computer-controlled flap operates to bring in the external air to cool the column oven rapidly—only 6min from 500°C to 100°C. This computer-controlled flap also ensures highly stable column temperature when it is set to a near-ambient point. The lowest controllable column temperature is about 26°C when the ambient temperature is 20°C... 

The fact that the mobile phase is heated by flow resistance as it passes through the column should not be overlooked. A rule of thumb is a 0.1 °C temperature increase per 1 bar pressure drop or 10 °C per 100 bar (0.025 °C per bar or 2.5 °C per 100 bar for water).It may be advisable to cool the column and work with low volume flow rates when very low-boiling mobile phases such as pentane (boiling point 36 °C) are involved. 

With ice water circulating in the water jacket to cool the column, the column was eluted with Freon-11. The eluent was evaporated to 100 pL and reconstituted to 200 pL with acetone. 

A number of techniques can speed up column cooling. These include purging the column by a cool inert or process gas (e.g., steam, nitrogen, fuel gas), liquid circulation, and water itqection. Water injection should not be applied when column temperature exceeds 200°F, or if any heat pockets are present. Guidelines 1 to 4 and 9 in Sec. 11.7 apply also to water injection for cooling the column. 

At shutdown the stiff was being steamed. After steaming, cold water was applied to cool the column. The sudden cooling caused a partial vacuum, and the stiff imploded. The open vent did not have sufficient capacity to relieve the vacuiun. 

TREF is another chromatographic method used to separate ciystallizable copolymers according to their chemical composition [101], It is used for polymers and copolymers of olefins like ethylene-VAc. These polymers only dissolve at elevated temperatures. A heated solution of the sample is introduced into the column which is subsequently cooled down at a critical rate after the flow has been stopped. After cooling the column is heated up again at a controlled rate while the flow of the eluent is started again. The copolymer chains dissolve at specific temperatures that are directly linked to their crystallizability, which is characteristic of their chemical composition. 

Cool the column to ambient before opening the column. Continuously monitor the tenperature. 

Minimize the number of open manways to reduce air entry and allow for rapid closure of the column if there is a fire. Do not force air circulation into the column. This may sound counterintuitive since air circulation will help cool the column if there is no fire however, fires can be prevented or stopped by starving them of oxygen. 

The modular system is simple and flexible. Modules can be selected to suit the needs of the operator and, for example, multiple detectors can readily be incorporated in the system, as well as analytical or preparative columns. This flexibility can be an advantage when faults develop, since modifications can be made without the need to cool the columns. Little or no automation has been developed for such systems, and most use manual injection. This has advantages in that fewer problems are encountered but care is required in preparing and handling hot solutions. Considerable manipulative skill and expertise is necessary if this is to be carried out safely and without precipitating the sample. 

To achieve cold trapping, the whole column, or just an inlet section, is cooled below the elution temperature of the component(s) of interest as long as sample introduction lasts. Afterwards the temperature is increased to start the chromatographic process. Cooling the column below the elution temperature by 100°C results in reconcentration by a factor of about 100. Cooling is, however, limited by the dew point of the solvent/carrier gas mixture lower temperatures cause flooding, and also solvent trapping. 

The following sequence of steps is repeated during sample analysis first, the peristaltic pump is switched on, and the sample loop is flushed with filtered seawater from the selected intake, while the cryogenic unit is operated to cool the column. Then, the 6-port valve is actuated into the sample injection position and the trapped seawater volume is forced into the purge vessel by the carrier gas stream. The sample is degassed, and volatiles are cryocon-... 

Whenever you change cylinders or regulators, be sure to protect the colunms in the chromatograph. Before you disrupt the gas flow, either switch to a second source of gas or, if you are disrupting carrier-gas flow, turn off the oven and cool the column supplied by the gas. 

The glass jacket shields the column from drafts and minimizes temperature variations from run to run. Air is blown through the annular space between the column and glass jacket to cool the column at the end of each analysis. 

After chromatographic conditions have been set to meet performance requirements, program the column temperature upward to the maximum temperature to be used and hold that temperature for the selected time. Following the analysis sequence protocol, cool the column to the initial starting temperature. 

Cool the column to at least 100 C before turning on carrier gas again. 

Blank—After conditions have been set to meet performance requirements, program the column temperature upward to the maximum temperature to be used. Following a rigorously standardized schedule, cool the column to the selected starting temperature. At the exact time set by the schedule, without injecting a sample, start the column temperature program. Measure and record the area in each time interval from the start of the run until the end of the run as specified in 8.7. Make a blank run at least daily. 

Column Conditioning—Both the TCEP and WCOT columns are to be briefly conditioned before use. Connect the columns to the valve (see 11.1) in the chromatographic oven. Adjust the carrier gas flows as in 11.3 and place the valve in the RESET position. After several minutes, increase the column oven temperature to 120 C and maintain these conditions for 5 to 10 min. Cool the columns below 60 C before shutting off the carrier flow. 

Cool the column to the starting temperature. Use identical conditions as used in 11.4.1. Inject 1 pL of the crude oil sample without internal standard (see 11.3.9). Record the area slices of each time interval through the end of the run. 

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. 

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