Overview

Gas chromatography columns are generally divided into packed columns and capillary columns. The packed columns are suitable for quantitative analysis of conventional samples, especially high-purity samples; capillary columns are suitable for separating complex or trace samples and residue analysis. For the time being, in the quantitative analysis of conventional samples and high-purity samples, it is often used to fill the column.

Gas chromatograph stainless steel packed column

The capillary column is generally a commercial column. After buying it, it can be used directly after aging. The packed columns are mostly prepared by themselves, and the efficiency of the packed columns has a great relationship with the preparation of the columns, especially the preparation of the filler.

The preparation of a 5% OV-101/Chromosorb WHP glass column is briefly described below, and the preparation of the packed column is briefly described.

First, the preparation of the column

1. Fixing of fixed liquid

0.5 g of OV-101 was weighed into a 200 mL beaker, dissolved in an appropriate amount of chloroform, and 10 g of the dried Chromosorb W HP carrier was slowly poured to completely immerse the carrier. The beaker was placed in a fume hood, dried under an infrared lamp, and continuously stirred until the solvent evaporated to dryness, then transferred to an oven at 110 ° C for 2 h for use.

2, the filling of the column

A small funnel was connected to the outlet of the column which had been washed and dried, and the prepared filler was filled into the column in portions while tapping the column wall until it was filled 1.5 cm from the column mouth. Move the glass funnel to the inlet of the column, plug a small group of silanized glass wool at the outlet end, and wrap it in thin layer of cotton or 2 layers of gauze, connect it to the vacuum pump through the rubber tube, and turn on the vacuum pump from the funnel. Continue to slowly add the prepared filler and tap the column wall to make it evenly packed. After filling, a small group of silanized glass wool is also plugged at the inlet end and properly pressed to keep the contents of the column from being moved.

3. Aging of the column

The column inlet is connected to the gasification chamber, and the outlet end is not connected to the detector, and the carrier gas (N2) is introduced at a flow rate of 15 mL/min. The temperature was raised to 250 ° C in stages and aged at this temperature for at least 24 h.

The above is a typical operation for the preparation of a chromatographic column using gas chromatography to detect the active ingredient of a pesticide.

Second, matters needing attention

1, the processing of the column

a. Glass column:

New column: Connect the hose directly with clean water for about 20 minutes, then rinse with distilled water, ethanol, and dry in an oven.

Note: Flushing method: Inhale distilled water or ethanol with a clean ear-washing ball, and then force the liquid into the column tube.

Old column (refer to the used column): directly attach the hose to the water for about 20 minutes, then pour the dilute acid (usually 0.1mol/L nitric acid or hydrochloric acid solution) into the column tube and let it soak for more than 2 hours. Rinse with water until the eluate is neutral, then inject ethanol or acetone in the same way, soak for 2 hours or more, then rinse with distilled water, ethanol, and dry in an oven.

b. Stainless steel column:

New column: washing and drying methods are the same as glass columns.

Old column: The washing and drying methods are the same as the glass column. However, it is necessary to replace the dilute acid with a dilute alkali, which is generally 0.1 mol/L sodium hydroxide solution.

2. The amount of solvent when fixing liquid is applied

The amount of solvent in the fixed liquid coating is the most difficult to grasp. Generally, the data describes "take the required amount of fixative solution and dissolve it with a proper amount of solvent (which can be immersed in the support)", and "the right amount (can be immersed in the support) What is the solvent? It is generally difficult to master. Here, tell everyone a simple method, weigh the required carrier, put it in the measuring cylinder, and measure its volume, which is the amount of solvent that dissolves the fixing solution. After the fixing solution is dissolved by this method, the carrier is gradually poured into the carrier, and the carrier is generally immersed. With a little stirring, the filler thus prepared is uniformly coated, and the coating is not thick and uneven, so that the column effect is poor. If the solvent is too much, it is easy to cause the upper layer of the carrier coating to be thick because the upper layer liquid evaporates faster.

3. Method of filling the column

When filling the column, pay attention to the uniform tightness of the filler in the column. Generally, the stainless steel column is better to fill, because the force is larger when the column is struck. The glass column is not easy, the tapping is light, the tightness is not enough. After the carrier gas is introduced, there will be a large gap in the column, which will cause a large dead volume and affect the efficiency of the column; if it is heavy, the glass column will be damaged accidentally. So pay attention to the strength of the beat. Sometimes, the filler is added again from the entrance after the column has aged.

4, column aging

When the column is aging, be careful not to connect the detector. Otherwise, the detector is easily contaminated.

The aging temperature must be greater than the column temperature at the time of use, so that the baseline will be stable when doing the analysis.

The aging time is generally 24 hours in a row. If there is difficulty, it can also age in time, as long as the baseline is stable.

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