What Column size should be used in Agilent 5975 MSD

[Analisis]

Hello:

In a Agilent 5972 GC coupled with a Agilent 5975 MSD with Diffusion pump we have been using for a long time a column DB-5MS 60 meter column with 0.25mm ID and 0.25um film thickness. I have read in the manual that the column lenght should be 30 meter. The question is if using a column of 60 meter would be a problem, because we have a very large noise in the column and I thought that this is because of our samples, but I am thinking if the
lenght of the column could have an effect in it, because the pump system, perhaps is not doing the best vacuum. We don't have a vacuum gauge to check the vacuum in the Analyzer. Also other question is if we use a 0.5 film thickness, would it better the problem of my samples?. Our samples in this case come from essential oils and this samples let a large amount of dirty in the liner and in the split outlet. This is a fragance industry and we check fragances from many types. I think that this samples have many components that charge the column but if we have a thicker film then the column can handle in better form this samples. What do you think?

Other question is if it would be better to use headspace in this samples? Waht we want to analyze is the fragance and this are volatiles, I think that this can be extracted with headspace and so we can solve the problem of the dirty samples, but I understand that not all the fragances can be extracted with headspace. What do you think?

Thank you!!

[Steve Reimer]

A 60 meter .25 column is OK if that is what you need to separate your target analytes. You don't mention flow rate or carrier gas so I'll assume you are running ~ 1mL/min of helium. That film thickness may not give you much retention for the most volatile compounds but may be fine for your fragrances.

Headspace analysis is one way to keep a lot of junk from trashing your inlet but makes quantitation trickier.

[Analisis]

Thank you Steve,

Yes I have Helium as carrier gas and 1ml/min column flow.
The problem with the samples is that are so charged with so many components that the column becomes contaminated very fast.
So I have thought that with a thicker film: 0.50 um instead of 0.25um the column will resist more load. Is that correct or no?
Also we want to add a precolumn. Well we want to change this column with a 30m x 0.25mm ID and 0.50 um film thickness. But as you said that there is no problem with 60m column I think we can go to 60m length x 0.25mm ID and 0.50um film thickness. What do you think?

Thank you!!

[benhutcherson]

Personally, as long as a 30m column of the same ID and stationary phase would separate my compounds of interest, I'd choose that any day over a 60m column.

Your analysis time will thank you.

[Analisis]

Thank you for your answer. Yes the analysis time today is about 146 min. too long. And with a 30 meter column the time should be lesser.
I will tell you what are the results when we have the new column.
Regards,

Adolfo

[Bigbear]

Do you use an inlet liner packed with wool?

[Rndirk]

Aren't frangrances compounds that are by definition at least somewhat volatile, already at room temperature? I don't analyze these compounds myself, but a headspace-type of injection sounds like a logical choice. There are different types of headspace, and I'm pretty sure people doing perfume analyses use 'sniffing' kind of devices to get the analytes on the column.

Again, I'm not talking from experience so correct me if I'm wrong.

[Analisis]

Do you use an inlet liner packed with wool?

Yes, we use a taper liner at the bottom with glass wool. It becomes dirty fast.

[benhutcherson]

146 minutes? Ouch.

With those kind of analysis times, I'd give H2 a serious look also. Aside from saving you a lot of money, it should cut your analysis time a fair bit(while maintaining resolution) in a similar column.

[James_Ball]

If you have enough sensitivity already you may want to go to a 0.18mm ID x 30m length column or possibly 20m length and use a higher split ratio at the inlet or dilute the samples. This will give you better vacuum, a faster analysis time with comparable separation and better sensitivity, and if you want to move to hydrogen it is easier to control the flow because the inlet pressure will not have to be in the 1-5psi range that is needed with a 0.25ID column to keep from having too much flow in the MS.