Transfer line temperature setting

[bugteller]

Hi all,
I understand that if the transfer line temperature is relatively lower than the GC oven temperature, some of volatilized compounds from column can be retained in the column section which is contained in the transfer line before they reach to the MS. Then, the transfer line temperature should be always same or higher than the maximum temperature of GC oven? Or, there is another possible setting that could be used without any problem?
Please advise.

Thanks
Dong-Hwan Choe

[Don_Hilton]

This depends on what instrument you are running. There are some older instruments that use the heat from the transfer line to heat the ion source. To control the ion source, one may have to run the transfer line cooler than the ideal temperature for moving compunds through the last few centimeters of the column.

So, in the ideal case, yes, you want the transfer line to be as warm as the GC oven or warmer. In reality, you may have to run at a cooler tempearature becase of design issues or limitations of materials in the mass spectrometer. The settings will varry depending on the instrument and the compunds of interest. You may have to try multiple sets of conditions and figure out the best compromise for your instrument.

[AICMM]

bugteller,

Remember, too, that the transfer line is at vacuum whereas the front of the column is at pressure. So compounds are going to stay volatile in the last third at temperatures considerably lower than in the first third. Even so, I would typically, as a rule of thumb, set the transfer line temp. at the same or +10 to the oven ramp max temp.

Best regards,

AICMM

[JI2002]

I understand that if the transfer line temperature is relatively lower than the GC oven temperature, some of volatilized compounds from column can be retained in the column section which is contained in the transfer line before they reach to the MS. Then, the transfer line temperature should be always same or higher than the maximum temperature of GC oven?

Dong-Hwan Choe

I've heard this agument many times, sometimes from the experts, but I don't agree. With the pressure near vaccum as mentioned by AICMM and linear velocity very large (close to sound speed maybe) at the interface, the analytes have no chance of being retained in the transfer line at lower temperature. I've not tried this, but you can set the interface temperature a little bit lower and compare the responses.

[Don_Hilton]

I have seen situations where analytes get hung up in the transfer line. The best solution is to try various conditions. If you cool the transfer line by several degrees, watch for retention times to increase and/or peaks to become wider. I remember this from a lab where we worked on HP5972s and a coworker was running PAHs. Some of the larger PAH's (5 ro 6 rings) showed this effect.

[Peter Apps]

The argument that analytes zip through the transfer line so fast that its temperature does not make any difference should also apply to the last several meters of the column that are in the GC oven - the MS vacuum does not suddenly go away at the end (beginning ?) of the transfer line. So if the transfer line is colder than the column there is a negative temperature gradient, which is bad for peak shapes, with no compensating change in gas conditions.

Intriguingly, the last time that I forgot to turn on a transfer line heater the peak profiles were perfect concentration overloading front tailed sharks fins.

Peter