Help needed: Issues with setting the carrier gas flow rate in a thermal conductivity cell gas chromatograph
Thread Content
For the thermal conductivity cell gas chromatography detector, when setting the carrier gas flow rate and adjusting the pressure before the column, should this be done after the temperature of the injector and the column has reached the set values, or before those values are reached, in order to achieve the desired carrier gas flow rate?
The last edit to this post was made by yuanyao9394 on 2010-10-22 at 11:32. To set the gas flow parameters, of course, the vaporization temperature and column temperature must first be adjusted properly.
Reply to 2# yuanyao9394: But after the column temperature rises to 80, the flow rate of the carrier gas decreases. This happens many times, and it keeps decreasing – what could be the reason for this?
There shouldn’t be any issue with the order of these steps, but the measurement of the column flow rate should be carried out once the instrument is ready. Modern instruments are equipped with flow control valves, so the flow rate should not change much. If there is a significant change, it might be due to problems with the column when it’s installed at that temperature, or there could be an issue with the flow control valve. A heat conduction cell with a flow rate of around 30 ml/min is generally sufficient
Reply to 4# chenhaidong5758: I agree; it’s sufficient as long as the flow rate reaches the required value during analysis. Moreover, changes in temperature can also affect the flow rate
The column flow rate is definitely determined after the temperature is ready. However, for packed columns, the flow rate of the carrier gas changes significantly before and after heating. For example, with a three-meter long packed column, if the column pressure is 30 kPa at room temperature, it can rise to over 150 kPa when the temperature is increased to 200 degrees Celsius. In contrast, for capillary columns with dimensions of 30*0.32, the pressure change is very small when the temperature is raised from room temperature to 200 degrees Celsius