Please help me to check if this method will work

[NinaWrong]

Dear all,

I am quite new on this field so I am seeking for help on the application of column DB-1.

I want to separate ethanol, acetic acid and ethyl acetate with DB-1 and FID. Do I have to dilute the mixture before injecting? If so, what kind of diluent would be suitable?

I found a Solvent Retention Data Table for DB-1 with column temperature etc.
http://www.chem.agilent.com/cag/cabu/pdf/b-0292.pdf

Thanks for any sort of help,
Nina

[dblux_]

... Do I have to dilute the mixture before injecting? ...

Dilute or split, otherwise you would overload your column.

[James_Ball]

If the concentrations of each are in percent levels, then I would dilute in water and use a 100:1 split with 1ul injection. The water will give a small solvent peak that should not interfere with your targets.

[Consumer Products Guy]

If the concentrations of each are in percent levels, then I would dilute in water and use a 100:1 split with 1ul injection. The water will give a small solvent peak that should not interfere with your targets.

I'd inject 0.5 microliter or less when solvent is water, as water expands so much in the inlet. And DB-1 type columns are not the best type for injections from water, water doesn't "wet" the film well. I might try a more-polar column - because ethyl acetate and ethanol won't be well-retained - such as DB-624 ("OK" with water as solvent) or PEG (good with water as solvent).

[NinaWrong]

If the concentrations of each are in percent levels, then I would dilute in water and use a 100:1 split with 1ul injection. The water will give a small solvent peak that should not interfere with your targets.

Thanks for the response. So water is okay to use as solvent for DB-1 column?

so if I have 3mL undiluted mixture, acetic acid:ethanol:ethyl acetate ratio as 1:1:1 (vv), and dilute with 10mL of water, it gives me

acetic acid 8.0375e-05 g/uL
ethanol 6.0598e-05 g/uL
ethyl acetate 8.9700e-04 g/uL

Then I use 100:1 split. I should be at least close to not overloading my column, right?

Thanks,
Nina

[NinaWrong]

Hello everyone,

I am quite new on GC field. With help from some people in this forum, I came up with this method, would someone please check if everything is reasonable?

I am trying to separate acetic acid, ethanol and ethyl acetate with DB-1 column at
Oven: 40 C for 5 mins, 40-260 C at 10 degree/min
Carrier: Helium
Injector: 250 C
Detector: FID 300 C


so if I have 3mL undiluted mixture, acetic acid:ethanol:ethyl acetate ratio as 1:1:1 (vv), and dilute with 10mL of water, it gives me
acetic acid 8.0375e-05 g/uL
ethanol 6.0598e-05 g/uL
ethyl acetate 8.9700e-04 g/uL

Then I use 100:1 split. I should be at least close to not overloading my column, right?

Thanks,
Nina

[dblux_]

If the concentrations of each are in percent levels, then I would dilute in water and use a 100:1 split with 1ul injection. The water will give a small solvent peak that should not interfere with your targets.

Thanks for the response. So water is okay to use as solvent for DB-1 column?

so if I have 3mL undiluted mixture, acetic acid:ethanol:ethyl acetate ratio as 1:1:1 (vv), and dilute with 10mL of water, it gives me

acetic acid 8.0375e-05 g/uL
ethanol 6.0598e-05 g/uL
ethyl acetate 8.9700e-04 g/uL

Then I use 100:1 split. I should be at least close to not overloading my column, right?

Thanks,
Nina

For your dilution scheme you will get: ethanol ca. 80 µg/µL and accordingly for rest of constituents.
If you inject 1 µL with split ratio 100:1 you will load your column with 800 ng of ethanol - perfect for 0.53 mm ID column.
But if your column is 0.32 mm you'd better reduce injected amount to 100 - 200 ng either by dilution or by increasing split ratio.
NB - film thickness influence for max. column load neglectet deliberately

[James_Ball]

If the concentrations of each are in percent levels, then I would dilute in water and use a 100:1 split with 1ul injection. The water will give a small solvent peak that should not interfere with your targets.

Thanks for the response. So water is okay to use as solvent for DB-1 column?

so if I have 3mL undiluted mixture, acetic acid:ethanol:ethyl acetate ratio as 1:1:1 (vv), and dilute with 10mL of water, it gives me

acetic acid 8.0375e-05 g/uL
ethanol 6.0598e-05 g/uL
ethyl acetate 8.9700e-04 g/uL

Then I use 100:1 split. I should be at least close to not overloading my column, right?

Thanks,
Nina

For your dilution scheme you will get: ethanol ca. 80 µg/µL and accordingly for rest of constituents.
If you inject 1 µL with split ratio 100:1 you will load your column with 800 ng of ethanol - perfect for 0.53 mm ID column.
But if your column is 0.32 mm you'd better reduce injected amount to 100 - 200 ng either by dilution or by increasing split ratio.
NB - film thickness influence for max. column load neglectet deliberately

If using the 0.32 or 0.25mm columns I would do 0.5ml sample to 10ml water with 100:1 split. Even with the 0.53mm column I would consider 1ml sample to 10ml water with 1:100 split. 1ul injections for either.

This would only put 0.01ul of water on the column which should be ok. I know DB-5 columns handle at least that much on a regular basis when doing purge and trap analysis so the DB-1 should be ok as well.

[NinaWrong]

If the concentrations of each are in percent levels, then I would dilute in water and use a 100:1 split with 1ul injection. The water will give a small solvent peak that should not interfere with your targets.

Thanks for the response. So water is okay to use as solvent for DB-1 column?

so if I have 3mL undiluted mixture, acetic acid:ethanol:ethyl acetate ratio as 1:1:1 (vv), and dilute with 10mL of water, it gives me

acetic acid 8.0375e-05 g/uL
ethanol 6.0598e-05 g/uL
ethyl acetate 8.9700e-04 g/uL

Then I use 100:1 split. I should be at least close to not overloading my column, right?

Thanks,
Nina

For your dilution scheme you will get: ethanol ca. 80 µg/µL and accordingly for rest of constituents.
If you inject 1 µL with split ratio 100:1 you will load your column with 800 ng of ethanol - perfect for 0.53 mm ID column.
But if your column is 0.32 mm you'd better reduce injected amount to 100 - 200 ng either by dilution or by increasing split ratio.
NB - film thickness influence for max. column load neglectet deliberately

Thanks for the information. It helped a lot. I am just wondering how you guys know the maximum amount of injection to each column. Is it written anywhere inside the operation manual or just from experience?

[James_Ball]

Thanks for the information. It helped a lot. I am just wondering how you guys know the maximum amount of injection to each column. Is it written anywhere inside the operation manual or just from experience?

Often you can find it in literature about the column at the column manufacturer's websites. I learned mostly from experience and reading any technical notes I could find along the way. You could also find it in things like the online seminars and training courses as those provided by this site.

Mostly is it not an exact number, it will vary by analyte and column type, but there are theoretical limits to how much a column of a certain diameter can process. If you see fronting on your peaks, or rounded tops, it is a good sign that you have exceeded that limit. If you see sign of like this, first try more dilution or greater split ratio and see if peak shape improves. Experience though is probably the best teacher.

[AICMM]

NinaWrong,

Can I propose you dilute with DMSO? This way you don't have to worry about water expansion. I am doing this now with ethanol analysis at percent levels (wine) and it seems to be working quite well. The only downside is that the DMSO elutes much later so you have to make sure it is off before next injection. This would only be an issue if you have to process hundreds of samples a day, if only 10 or 20 not that big a deal.

Your components should be soluble. I use a bigger dilution and a smaller split ratio (saves gas.) Injecting 0.5 uL. I also have added IS to the DMSO to account for split injection variability.

Best regards,

AICMM

[Bigbear]

If injection water I wouldn't go higher than 120C for the injector.