Carrier gas flow rate in capillary column
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I have a question for you masters: Why is the carrier gas flow rate in the capillary column so low as only 1-3ml/min? Can't the carrier gas flow be adjusted to increase the flow rate? Thanks
The inner diameter of the capillary column is small, and the flow rate will not be too high. It is difficult to measure the flow rate accurately with a soap film flow meter. Generally, the pre-column pressure can be increased to increase the carrier gas flow rate. This post was last edited by flks224086 on 2009-3-27 18:32 ]
It's all in the instrument analysis books. I seem to have done this homework before, but the teacher said no.
Capillary columns have small column diameters and long columns, so the column resistance is large and the flow rate is low. Increasing the column pre-pressure will not increase the column flow rate much. The advantages of capillary columns are small injection volume, small carrier gas flow rate, and good separation effect.
Because the inner diameter of the capillary column is small, the volume flow rate of the carrier gas is still very small even if a high linear flow rate is used.
Usually the soap film flowmeter measures the carrier gas flow rate under the temperature and pressure conditions at the outlet of the detector or column. Since the gas is compressible, although the mass of the carrier gas passing through any section of the chromatographic column per unit time remains unchanged, the volumetric flow rate is also different because the carrier gas pressure and density are different everywhere in the column. The average linear flow rate of the carrier gas in the capillary column describes the forward speed of the carrier gas in the column, which varies with the inner diameter of the column when other conditions remain unchanged. u=L/tm (cm·s-1) L——column length tm——dead time
Capillary chromatography columns are divided into large diameter and small diameter. Of course, different inner diameters have different flow rate requirements. If you want to increase the analysis speed, you can increase the flow rate, but you can also increase the temperature of the column box. If it is really not ideal, you should consider changing to a different type of chromatographic column.
It can be increased, but not too high. It is best not to exceed 5ML/minute.
Although the packed column is short, the column resistance is much greater than the capillary column resistance. Why can the carrier gas flow rate be so high?
Does the column resistance of the capillary need to be large? ? ? Its pipe diameter is smaller, it has more columns and is longer. See the 6th floor.
The flow rate can be increased by increasing the flow rate, but doing so may result in reduced resolution
Back on the 9th floor, the diameter of the packed column is about 3mm (1/8 inch), and the diameter of the capillary column is generally 0.32mm. The approximate tube cross-sectional area ratio is 100: 1. Considering the particle accumulation rate in the packed column, the void rate is about 30%, and the ventilation area ratio between the packed column and the capillary column is about 30: 1. Of course, the specific pipe diameter will vary, but in general, the ventilation area of capillary columns is much smaller than that of packed columns. ； The length ratio of capillary columns to packed columns is generally about 15: 1. The friction resistance is also large. The analysis is very general, and the data is just a general estimate. If there are any errors, please point them out. Don’t be merciful.~~
Can anyone tell me why the column resistance of packed columns is greater than the capillary column resistance? ? ?