From the information supplied with my GC column, the upper temperature limit for it is 325°C.
However I do have another temperature in brackets next to it for (350°C). Does this mean that 325°C is the upper analytical limit, or the upper limit full stop for the column?
And if it is the latter what does the 350°C refer to?
By Anonymous on Wednesday, July 16, 2003 - 06:35 am:
Sometimes the figure in brackets is the upper limit for temperature programming application, whereas the lower limit is for isothermal use. This assumes that the column will only be at this temperature for a brief period in a progammed run and will be less susceptible to phase loss or degradation. This does not seem a very scientific approach to me because it al depends on how you define "brief period". However, there it is.
By Jason Ellis on Thursday, July 17, 2003 - 09:27 am:
In your example, 325C is the "isothermal limit" meaning you can take the column to 325C and hold it for a long time without causing excessive stress to the phase; 350C is the "temperature program limit" meaning you can take the column to 350C if you need to, but only for maybe 5-10 minutes at a time maximum. It's really a judgement call: if you need to take the column above 325C for your application (ie. to elute heavy compounds faster) then you can use that extra 25C, but you don't have to. Between 325-350C you are stressing the phase more so you will see additional bleed and theoretical loss of lifetime, however you need to balance those cons with the benefits of reduced retention times for late eluters and the possible resolution gains you may see for those late eluters.
GC Column Tech Support
By Anonymous on Wednesday, July 16, 2003 - 05:42 am:
The first temperature is for isothermal operation. The second is for a programmed oven which does not remain at that temperature but reaches it and then immediately cools to a lower temperature below the isothermal limit(325°C).