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How to obtain gas chromatography with higher sensitivity?

2023-12-19 17:22

How to obtain gas chromatography with higher sensitivity?

The main method is to use solvent concentration, which aims to obtain sharp peaks without using split injection. Only in this way can better sensitivity and separation be achieved.

Solvent concentration is produced by two methods:

The first method is used for both non split injection and direct injection:

This method requires adjusting the column temperature box. The difference from the former is that the solvent and analytical compound must be cooled and condensed simultaneously on a cooler chromatographic column during injection;

These condensed samples form a "flooded zone" on the surface of the chromatographic column;

As the solvent gradually evaporates, the area of the sample flooding zone gradually decreases, and the concentration of the analyte in the "sample flooding zone" gradually increases.

After the solvent has completely evaporated, the analyte will condense on a small range of column surfaces.

The second method is to cool and condense the liquid sample on a cooler chromatographic column after it evaporates without splitting the sample:

The volume of the carrier gas is much larger than that of the liquid, so when the sample condenses, it is concentrated within a small range of the chromatographic column.

So regardless of the method, the analyte or solvent and analyte must condense on a small area of the column.

The factors that affect the coagulation rate of the sample on the chromatographic column include:

The initial column temperature of the chromatographic column, the volatility of the solvent, and the ratio of the stationary phase in the chromatographic column.

Initial temperature of chromatographic column temperature:

1. Basically, it is the easiest and fastest method to achieve. Generally speaking, the lower the initial temperature, the better the analyte solidifies.

2. It is recommended to set the initial temperature at around 50 degrees Celsius lower than the boiling point of the analyte with the fastest peak, and the best time to maintain the temperature is for non split flow.

The second important factor:

Phase ratio of chromatographic column:

The lower the proportion of fixed phase, the thicker the film, and the easier it is for the sample and solvent to dissolve in the fixed phase. To change this factor, one can only try different pillars. This is the method used when changing the initial temperature is impossible to achieve.

The last factor that can be changed is the sample itself:

Most of the time, the sample itself cannot be changed, but different solvents can be used to increase its effectiveness. For example, the greater the difference between the boiling point of the solvent and the initial temperature, the better. For example, when the initial column temperature is 30 degrees Celsius, the solvent used in the sample is ethyl acetate (boiling point 77.1 degrees Celsius), which is better than using dichloromethane solvent (boiling point 39 degrees Celsius).

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