Chromatography Forum

Hello all,

I am running a standard solution using toluene as solvent.

The injector temperature set at 280C
flowrate: 1.0 ml/ml

initial column temperature : 80C

The problem is when a running in splitless mode, everything ok and the signal is very strong and sharp.

However when running as split: initial " ON" as 1:10 then "0.5 min" split 1: 100 , I got less than 1/50 of intensity of corresponding splitless peaks and the peaks were tailing.
Changed as initial " ON" as 1:10 then "0.5 min" "off". same thing happed.

Does anybody have same issue like mine?

Thanks lot

When running split you should not change the split ratio during the run.

If it works well splitless, why try to run split ?

Peter

Hello

Changing from splitless to split one would expect a decrease in intensity.
So Split 1:10 gives roughly a 1/10 of intensity (keep in mind changing split ratio does not have a linear correlation to the peak intensities.)

I understand why one would increase the split after certain time: i have seen methods that use this to clean the liner to prevent carryover and reduce ghost peaks.
I also understand why one would reduce the split after certain time: I use it to save carier gas (He is expensive these days)

Changing the split ratio after 0.5 min seems a little bit early.
It could be that you are in the middle of transfering your sample to the column.
Changing the split ratio during transfere will have certainly adverse effects on your analysis.
I usualy wait several minutes before I change split ratio.

However i would not recomend to swich off the split completely.
Even wenn you do splitless injections, after a certain time (sampling time) the split is open, to get rid of the remaining sampel in the liner.

Andi

Hi All,

Thanks for suggestion.

I have tried using this mode: initial 1:10 then 5 min 1:100. did not work and the intensity of peaks were very small.

But when I tried this mode: initial: off, then 0.1 min (or 0.5 min) 1:10 split then 5 min 1:100 min. the signal intensity of peaks were slightly less than those of splitless. it seems that samples were evaporated in injector for just seconds and could not effectively transferred to column when the split mode was applied.

Thanks again.

You need to check the installation of the column in the inlet - the symptoms that you describe can be due to the column being inserted too far into the liner so that sample is released from the syringe needle below the column tip. With splitless injections the sample vapour still goes to the column because there is no other way out of the inlet, with split injections nearly all of it just blows out of the bottom of the liner on its way to the split vent.

Peter