Ethanol analysis by GC/FID...need help

[Rick]

Hi!
I have to analyse ethanol by GC/FID and split injection mode
What is the capillary column i need?
Thank you!

[Schmitty]

I've used 1s, 5s and Waxes with success.

[chromatographer1]

Also a good choice is a 30 or 60m 1301 or 624 phase capillary, 0.53mm and 3µm phase optionally use a 0.32mm ID column.

[Rick]

Thank you for your response...What is the best temperature programmation for?
I have read 40c / 1min----15c/min---180c/10min
What do you think about this programmation?
Thank you!

[chromatographer1]

I would hold the temperature slightly longer at the beginning (2 min?) and program the oven at a lower rate (8°C/min?). I would use the high ending temperature only if you routinely find impurities in your ethanol eluting at that temperature.

best wishes,

Rod

[Schmitty]

My current setup is a 30x0.53mm, 2µ Wax, with inj port at 150 and detector at 250. Oven is 40 for 5 min, then 15°C/min to 23, 230 for 2 min. FI detector. Standards and samples are in 20mL headspace vials with 10mL water. No internal standard for me, but some people need 1-Propanol because of matrix effects.

How's that?

[chromatographer1]

Headspace can be a wonderful tool. I am sure you have very reproducible results, especially if you are automated.

I am curious, do you achieve adequate resolution of Isopropanol from ethanol? or is it tight? and do you use headspace to reduce the amount of sample on column to improve resolution?

What late eluting impurities do you find in ethanol? acetic acid in trace amounts? adulterants? Any amines? Are you checking reprocessed solvent from a manufacturing process or checking new stock from a vendor?

Thanks in advance for the information.

best wishes,

Rod

[Schmitty]

Headspace can be a wonderful tool. I am sure you have very reproducible results, especially if you are automated.

I am curious, do you achieve adequate resolution of Isopropanol from ethanol? or is it tight? and do you use headspace to reduce the amount of sample on column to improve resolution?

What late eluting impurities do you find in ethanol? acetic acid in trace amounts? adulterants? Any amines? Are you checking reprocessed solvent from a manufacturing process or checking new stock from a vendor?

Are you asking me or the OP?

The analysis I do is headspace (CTC CombiPAL). We use large volume injections (1-2mL), mostly because we don't want to modify the method. The linear range is excellent 1-2000ppm or so. The IPA and EtOH are not resolved with my setup. But, if one is not completely humungous in size compared to the other, then there are no problems integrating or calibrating.

We are only analyzing raw products for our clients...we look for what they ask. If there are "mystery peaks" in their sample, they will continue to be mystery peaks

[Consumer Products Guy]

We use Nukol, a PEG column, 0.53mm. Inject 0.5ul of aqueous solution, at 40C isothermal. n-propanol fine as internal standard, this column will NOT readily separate ethanol from IPA.

[Bob M]

In my experience a standard 0.5 mm bore carbowax column is OK if you have a nice clean sample. If your sample is raw beer or somthing similar save your capillary column and use a chomosorb 101 packed column. On one ocassion I wrote off a new 50 metre capillary column with a crappy sample. I own the lab so it was money straight out of my own pocket OUCH.

Bob M

[sadsal123]

I am using an Elite-624 Capillary Column (30m X 250um ID X 1.4mm Film Thickness) and we put all kinds of solvents / mixtures through the GC and the method works fine (as long as the sample has been filtered through a 0.45micron filter). If its just ethanol you are looking for then try starting your programme at 50oC hold for 3mins, then ramp it at about 8oC/min. If you are using IPA in your mixture, then you will have problems separating your Ethanol and IPA peaks with your current set up because you are ramping too fast.

If you want to speed up your run time, it might be an idea to ramp at 8oC/min for about 10-15mins, or until your ethanol and IPA elute, then hold for 3mins and then ramp at 15oC/min to 230oC.

I hope this helps,

Good Luck.

Salma

[dhruvil]

hi, this is dhruvil.
i m working with research and development department of a pharmaceutical company. and i m analysing ethanol by head space method in almost every drugs. so i will suggest u to use DB-624 (30m x 0.32 mm i.d. x 1.8 um) capillary column. and the other chromatographic comditions also u can note down.

injector/detector 180 / 250 C
split ratio 4:1 (or adjust suitably, according to the response or your standard preparations)
Oven temp. 40 hold for 3 min. ----@ 20 C/min. to 220 C hold for 10 min.
linear velocity 35 cm/sec....
conditioning temperature of the vial---- 80 C
conditioning time of the vial ---- 10 min.(with agitation)/15 min.( without agitation)
injection volume --- 1 ml
syringe temperature---- 120 C

just check it out by this method....and choose a good diluent..(do not worry about the dissolution, your sample need not be dissoved for the headspace analysis), ok

ok then hope that this will solve yr problem and hope i am correctly replying for your problem...i mean i guess this only is the problem you r facing.

ok then
bye