GC oven: Isothermal or temperature program ?

[thohry]

As we often do: run simple samples in isothermal oven temp, and temperature program is for complex samples. But I do not know how to decide which ones are simple and which are complicated ?
Anyone know a rule from that we can decide isothermal or temp programming.

[Peter Apps]

Temperature programming has two effects - it speeds up the elution of late-eluting compounds, and it improves their detectability by making their peaks narrower, both of which are desirable.

The drawback of programming is that you waste time waiting for the oven to cool down again before you can start the next run.

So the rule is; if you can get adequate separation and detectability with an isothermal run in less time than it takes to achieve the same with programming including the cooling, then use isothermal.

Peter

[chromatographer1]

Peter's comments are good.

Let me add comments.

If critical separations are achieved early in the run and late peaks can be seen well, then run isothermal, unless run time is excessive.

If sensitivity is poor in the analysis then programming is usually a better choice.

Ultimately, rules are only useful if they apply. Sometimes time or a critical separation is more important. Other times separation and detection over a wide temperature range has a higher priority.

You have to decide for yourself the better path in each application.

Rod