Chromatography Forum

Hello everyone!

I have a problem since I need to add 1% Krypton in our system
I usually use a Packed Mol. Sieve 5A 100/120 8' long to separate 20% Nitrogen,1% CH4 from Oxygen and the detector is TCD.
But you know,Krypton will elute with Nitrogen on a Mol.Sieve 5A column.
Possibly Hayesep D could separate Nitrogen from Krypton,but I worry about the separation of Krypton and Methane on a D column.

Do you have any idea if another column would be better to separate the three impurities from O2?

Thanks in advance.

No Problem.

Add a 2 foot Carboxen 1000 to your Mole Sieve 5A combined column to separate Oxygen, nitrogen, krypton, and methane.

The Carboxen column will separate N2 from Ar by 30 seconds at 40C and 30cc/min helium or hydrogen carrier.

been there, done that.

Rod

Thanks very much. Rob

I'll try this column

Mlee

I made a typo error.

The separation is not 30 seconds, but 90 seconds.

And the name is ROD, not Rob. But I can forgive. See the first sentence of this post.


Here are retention times for a 3ft and a 2ft columns in series

3ft MS 5A 2ft Carboxen 1000 combined 5 ft column

tr minutes
Neon 0.151 0.092 0.263
Oxygen 0.328 0.390 0.833
Nitrogen 0.877 0.390 1.563
Krypton 0.877 1.847 3.005

Your present mole sieve column with a 1 to 3 ft Carboxen 1000 column will work wonders.

Rod

Very sorry for my mistake.Rod

Appreciated for your advice.
BTW,Could you suggest the RT of methane on 2ft Carboxen 1000?
From the chromatogram of Carboxen 1010 PLOT, Krypton interferes with Methane.

Mlee

When I have time I will try to look up that information. I believe the retention time is very close to Kr.

Edited ON: the retention of methane on a C-1000 column is about 4 times the retention of nitrogen.
VERY CLOSE to Argon. Edited OFF

I know you need BOTH columns to get the separation you need.

The most simple answer is to determine how much time the Kr is retained behind nitrogen on a 2 or 3ft column and then use a MSieve 5A column that will retain methane half that time behind nitrogen.

Since the C-1000 is stronger retaining Kr behind nitrogen than a MS5A is retaining methane behind nitrogen, you need a short C-1000 column and a long MS5A column.

Quickly offering a

guess ,

I think a 8 ft MS 5A will require a 3 ft Carboxen 1000.

But I would buy a 1, 2 and 3ft Carboxen 1000 (giving you 1, 2, 3, 4, 5, and 6ft combinations);

and to go with your present 8ft column

a 4ft and a 10ft MS 5A (giving you 4, 8, 10, 12, 14, and 18 ft. combinations).

[ 5 packed columns at a price that perhaps a single 60 meter capillary would cost you ]

And don't forget the 1/8 inch bored through SS unions to connect the columns together. One of these combinations should do the trick, no?

best wishes,

Rod

So professional,Rod

I'll update the result to you once finding the best combination.

Oops, I forgot to warn you.

Many cylinders of commercial nitrogen have a goodly amount of Kr already present.

Many commencial blends also have Kr because of that reason.

Just though you might want to chech on that before you add more Kr to your gases.

best wishes,

Rod

Mlee.

Any news?

Rod

I analyse for 0.1-1% levels of these in oxygen matrix using a 2m x 1/8" packed molsieve 5A column, He carrier, starting at 75C and they all separate. Nitrogen (maybe 5% vol) comes off about 3min, Kr at 3.7, methane about 4.8.

If your balance is something other than nitrogen, this narrows the peak width of N2 and Kr on the backside of N2 will give adequate separation as you have seen.

But if N2 is too large and Kr too small it becomes difficult to use only a 5A MS column, especially if a lower than 75C temperature is required as the peaks are less sharp.

If you can post a chromatogram I am sure many would be delighted to see this separation as the 8ft column
Mlee is using was not able to perform the separation (sample size, flow path dead volume, detector, and of course the quality of the packing all have a bearing on the results)

Any news, Mlee?

Rod

et voila

250ul loop, 53psi helium (isobaric), temp ramp at 10C/min from 2.5min. Change in TCD sensitivity following the oxygen matrix peak hence the jump in baseline.

Bump. I edited my previous post to put the pic in and didn't realise the time stamp would stay the same. Anyway hope this helps.
John

Congratulations, John.

Your column seems to be well packed and the material is of excellent quality.

Where did you obtain the column?

(curious minds want to know)

Your detector response for oxygen is one I have not seen. I am used to thermister types and of course, the ubiquitous Agilent microTCD. Is the detector a Gow-Mac hot wire or a electronic sensor detector?

(curious minds want to know)

Thanks for the chromatogram.

best wishes,

Rod

Hi Rod
This was on a dual-channel Varian 430 with TCD (one column up each side), we also run it on a 7820 (micro TCD) but there is no ability to change in the sensitivity setting (neither does it error when the matrix peak passes through). The former is a few years old at least now, supplied by Varian I think, the latter is new this year with columns supplied by Agilent. All we do is gas analysis so nothing has a particularly hard life.
John