Column chromatography (1)

Chromatography is also called chromatography or chromatography

Column chromatography is a physical separation method

There are three types of methods for separating products with chromatography columns: normal pressure, positive pressure (called pressure during operation) and negative pressure (called reduced pressure during operation).

The two methods of positive pressure and negative pressure destroy the distribution balance of the mixture in the solid-liquid phase, the separation effect is not as ideal as the normal pressure method, and the amount of eluent is large, but the two methods of positive pressure and negative pressure improve the distillation The effect of speed, especially when using a very fine stationary phase above 300 mesh and a light mobile phase composed of PE&EA, the two methods of positive pressure and negative pressure can show their advantages

There are three methods of pressurization: air pump pressurization, nitrogen pressurization and double-ball pressurization

1.

In order to conveniently pressurize the chromatography column, some laboratories adopt small electric air pumps to directly pressurize the column (air).

There have been many accidents caused by the use of pressurized air pumps

Figure 23-1 is a scene after a fire was caused by a pressurized pump, and Figure 23-2 is a face scar after the burn treatment of the person involved

Figure 23-1 The scene after the fire

Figure 23-2 Scar after facial injury

If you must use a pressurizing pump to pressurize the chromatography column, the safety distance must be guaranteed, that is: keep the air pump away from the chromatography column, which needs to exceed 2m; the power socket and the air pump plug should also be far away from the work area (that is, the chromatography operation and Storage area for mobile phase preparation)

2.

Column chromatography is carried out under nitrogen pressure, which eliminates potential safety hazards caused by electric sparks or short circuits

The method of using nitrogen pressurized column chromatography is as follows:

(1) As shown in Figure 23-3, set up the device.

(2) Pour the eluent in advance and then connect the pipeline, tie it tightly with a rubber band to fix the connection part and make the air path unblocked

(3) Open the main valve of the nitrogen cylinder, carefully adjust the pressure reducing valve until the flow rate of the eluent is moderate, and pay attention to the buffer balloon
.

(4) Do not close the cork valve at the bottom of the column when you connect a bottle of eluent and change the bottle, so as to prevent the pressure from blowing up the balloon and the chromatographic silica gel to affect separation
.

(5) When adding eluent, first close the main valve, open the pressure relief port until the pressure in the system is normal, then take out the three-way, and pour in an appropriate amount of eluent (do not move the pressure reducing valve to avoid re-adjustment next time waste time).

(6) After adding the eluent, connect the pipeline, tie it tightly with a rubber band to fix the connection part, and then open the main air valve
.

(7) Repeat the operations (4), (5), (6) until the separation ends
.

(8) The above is an intermittent operation.
If continuous operation is required, a suitable device can be added to the eluent bottle to increase the eluent without interrupting the positive pressure of the system
.

The advantages of nitrogen pressure column chromatography: the pressure of nitrogen pressure chromatography is constant, the flow rate is uniform, the operation is convenient, and it avoids electric sparks, and nitrogen is an inert gas, thus avoiding fires and greatly improving safety
.