Chromatography Forum

Hello,

I'm using DB-624 column-75m 0.53mm and 3um.
I'm getting some strange noise peaks that I can't explain
Temperature program starts at 50c and ends at 220c.


The problem starts as soon as the gc reaches 220c.
I have tried to condition the column for 2 hours but it didn't help.

Hello

There are at least few possible reasons. But first of all...
Could you provide parameters for your methods?
Don't you think that information about type of detector could be helpful?

Regards

Tomasz Kubowicz

Instrument is agilent 7890B with FID
Method parameters:
Inlet temp.- 140c
Detector temp.- 260c
Flow- 3.3ml/min- Helium
Diluent- DMSO
Column temp program:
50°C for 15min - 8°C/min to 120°C- 35°C/min to 220°C for 15min
I'm using CTC/PAL headspace sampler

The method is for 6 residual solvents-Ethanol, Methanol,IPA,Ethyl acetate, Toluene and Dichloromethane.

The method is working with no problems and RSD values for all solvents is below 10% but in all the chromatograms the same problem appears (the attached chromatogram is without any injection)

What is the max temperature of the DB-624 column?

I haven't used the J&W columns lately but I know the standard 624 columns normally have max temperatures around 230C. If so, then you are seeing the increased bleed coming from the column being at or near its max temperature.

How large is the baseline rise compared to your lowest standard peaks? I can't read the scale so I don't know if the baseline rise is just a result of auto-scaling or if it is large compared to your expected response.
220 degrees is a normal end temp for a DB-624.

If you are getting rsds of less than 10% your analytes must be eluting on the clean baseline - so why torture the column by taking it close to to its maximum temperature ?

Peter

Hello

I think what you have is bleeding from column - 3um stationary phase will give higher baseline disturbance when it is baking out in 230.
Plus...column is 75m so perhaps something has been acumulated (for long time) and it is coming out in 230.

Regards

Tomasz Kubowicz

Here is a chromatogram of standard injection:


Only toluene is close to the noise.
The temperature limit for the column is 260°C, so 220 is fine.
What could cause the column to degrade besides warming it over the limit?

You have a ton of resolution to spare - you could do this analysis on a 15m column at lower temperatures.

Column degradation is due to high temperatures, oxygen or water in the carrier gas (use a scrubber upstream of the GC) and, more rarely, water in samples.

Peter

I have a 50:50 methyl:phenyl column that does the same thing to me (flame detector). I've never had another column behave like it. No matter how long I bake it out or how frequently I use it, the same thing happens. Merely sitting installed in the oven over night and I get the same junk. The only think that I can think of is that it's just not coated very well. I have an Rtx-624 that I use frequently and has an upper limit of 250 °C. It's a pretty thick film as well (1.8 µm) compared to the i.d. and it doesn't bleed like what you show.