Temperature gradient for MSD transfer line (bakeout)

Good afternoon,

 

I am investigating the possibility of measuring diketones in a matrix of glycerol, which has a BP of 290*C.

The column I'd like to use is the VF-624ms 30 x  250 x 1.4, with the idea that this column is in-house and has heat resistance up to 280*C isocratic or 300*C gradient.

The up to 300C will allow me to bake out the glycerol after each run, but in my preparation, I wondered what to do with the MS transfer line temperature.

 

If I would set the MS transfer line to the isocratic maximum of 280C, I'll just be left with a glycerol buildup inside the column. Or is the drop in pressure due to the MS vacuum enough to keep glycerol in the gas phase? And if I would set the MS transfer line at 300C it will bleed the column bone dry, creating active zones at the end of the column.

 

Is there any way to have the MS transfer line temperature increase in tandem with the GC oven temperature gradient?

 

I understand that a Headspace method or buying a different column with a higher heat capacity while being more polar would help but unfortunately, that is not a current option.

 

Thanks and have a good day!

 

 

Instrument:

7890B GC, 5977B MS, VF-624ms column (-40*C to 280*C isocratic, up to 300*C for gradient)

Masshunter GC/MS Acquisition B.07.04.226

Parents
  • Hello Koos,

     

    We often analyse samples containing glycerol on a 624 column (60 m), and glycerol elutes at an oven temperature of  200°C. (oven temp from 30 to 300° at 8°C/min)

    BTW we use the  Restek Rxi-624Sil MS column which has 20° higher rtemperature limits.

     

    Hope this helps,

    Henk

Reply
  • Hello Koos,

     

    We often analyse samples containing glycerol on a 624 column (60 m), and glycerol elutes at an oven temperature of  200°C. (oven temp from 30 to 300° at 8°C/min)

    BTW we use the  Restek Rxi-624Sil MS column which has 20° higher rtemperature limits.

     

    Hope this helps,

    Henk

Children
  • Good morning Henk,

     

    Yes, the glycerol peak elutes way before the boiling point temperature is reached, and this created a false sense of security in our lab that everything eluted.

    The old method used a DB-Wax column up to the temperature of 260*C and you saw a glycerol peak elute clearly. However with each sequential injection the response of the compound of interest decreased. The internal standard response dropped equally, cancelling out the effect and having useable data. As you can guess, this was fine at first but is starting to cause problems in the long run. 

     

    This is the reason I'm redeveloping the method. It is suspected now that glycerin remained in the column, building up and absorbing the compound of interest during sequential runs. 

    ^ Typical chromatogram of the old DB-Wax method showing the eluting of glycerol. On the right the loss of signal of the compounds of interested, without correction using ISTD.

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