Hello everyone

Recently we have focused on gas chromatography column process

The problems encountered are briefly summarized

For your reference

1. What will be the impact on the GC column if the pH value of the sample is too high or too low?

The influence of too high or too low pH value of the sample on the chromatographic column is mainly to cause pollution or damage to the liquid film. Due to the limited injection volume and split flow of the gas chromatography, this effect has no fixed value. In theory, it is recommended to pH The value should not be too large or too small, and the pH value should be kept between 5-10 as much as possible.

2. Under what circumstances might the sample interact with the chromatographic column, and whether the substances in the chromatographic column may be carried out?

The stationary phase of the chromatographic column is an organic polymer, and the sample generally does not react with the chromatographic column, but some special sample components will destroy the polymer, and the reaction will change the polymer characteristics, resulting in the oxidation of the liquid film, corrosion of the liquid film, Salt accumulation contaminates the liquid membrane. Although this effect is slow, the contaminants cannot be eliminated and will cause permanent damage to the chromatographic column.

3. The sample contains a small amount of water. Can it be injected directly and what effect will it have on the chromatographic column or detector?

Water will dissolve the liquid film of the chromatographic column, causing the liquid film to fall off or become more uneven, which will reduce the column efficiency. In addition, the thermal expansion volume of water is large, which will change the shape of the chromatographic peaks. If the split is small, it is generally recommended that the moisture does not exceed 10% of the sample volume. Excessive water content can also affect the stability of the detector resulting in poor reproducibility.

4. What are the requirements for the boiling point of the sample for headspace injection, should the furnace temperature be higher than the boiling point of the substance?

The headspace method generally tests samples with a boiling point below 150 °C, and the headspace equilibrium temperature is generally 20 °C above and below the boiling point of the sample. The headspace method can only reach up to 90 ℃ with the water bath method, and can reach 150 ℃ with the oil bath method, which depends on the choice of different samples.

5. The inner diameter and film thickness of the chromatographic column are different, what is the appropriate setting for the flow rate of the carrier gas?

The inner diameter and film thickness of the chromatographic column have a certain relationship with the flow rate. Generally, the maximum pressure of chromatography is 0.3MPa, the column flow rate of the chromatographic column with the inner diameter of 0.25mm and 0.32mm is recommended to be 0.5-2mL/min, and the recommended flow rate of the chromatographic column of 0.53mm is at 2-8mL/min.

6. Can phosphate be analyzed by gas phase?

It depends on whether the sample can be vaporized. If it cannot be vaporized, it cannot be tested. Generally, the sample solution containing inorganic salts cannot be tested, otherwise the liner or column will be blocked.

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