Molsieve 5A

[peridem79]

hi there everyone

I have a new Molsieve 5A column that is regenerated. I installed it in the GC HP 6890. The Molsieve and Porapak Q are connected in series. When I run my analyses I dont get any peaks from the Molsieve why is that?

[chromatographer1]

Do you have a leak?

Have you run the MS5A by itself to see if it is the problem.

No peaks either means the sample did not get

to the column

or

through the column

or the detector is not working.

Run samples through the Q column only and see if everything but the MS5A is working.

If the MS5A column worked before you reconditioned it, then I would have to ask you to detail with specifics, how you regenerated the column.

They can be damaged by improper use and/or conditioning.

best wishes,

Rod

[peridem79]

Im new with GC so I dont have so much experiences.
Since the columns are connected in series I do see the compound from the Porapak Q but not from the Molsieve. The Molsieve is new, have not used it before.

The column have conditioned with oven temp 5 min. at 50 °C , and than we have a ramp 2°C/min to 100 °C for 60 min later 2°C/min to 350 °C over night.

I have to check if we have leakage when the column is installed.

When I install the old column we do see the compounds so it cant be detector.

[chromatographer1]

Check and see if you get flow through the MS5a column.

If so they you should be seeing N2 through it.

If you have no flow then check for leaking fittings.

If you have a blocked column then return it.

Did you buy the column from stock or was it custom freshly made?

Did the maker condition it?

I know the folks at Supelco who make and condition their columns but other vendors I do not.

best wishes,

Rod

[chromatographer1]

About conditioning a MS A column.

You should never need to heat it beyond 250°C overnight, unless you are trying to get the last 5-10% of resolution between N2 and O2.

Slower the conditioning the better.

Faster the dry carrier gas the better.

I hope chemistry did not bite you in the lower abdominal area, dorsal side.

Treat MS columns like they were made out of crystals, fragile crystals, and you will be better off.

Rod

[AICMM]

peridem79,

Did you remove the Porapak before you conditioned the mol-sieve overnight at 350C? If not, you may have destroyed the Q which might not let anything through at this point.

Best regards,

AICMM

[peridem79]

Chromatography1
Thank you for the answear! I will try to answear your questions its not so easy since I cant handle the GC so much.

Check and see if you get flow through the MS5a column.
I do have a flow trough the column.

If so they you should be seeing N2 through it.
I dont see any compounds trough this column, only a nice baseline

If you have no flow then check for leaking fittings.
The GC is old and Im sure that we have leaking in the fittings.

If you have a blocked column then return it.
I have done the conditioning. Can the column be blocked due to conditioning?

Did you buy the column from stock or was it custom freshly made?
The column is custom made.

Did the maker condition it?
I dont think so since when I made the conditioning, the column looks very old in the colour

[peridem79]

AICMM

Yes I did remove the Porapak Q.

[chromatographer1]

I would contact the vendor for the column and explain what you are seeing and ask them to replace the column.

Rod

[chromatographer1]

I forgot to answer one of your questions:

"If you have a blocked column then return it.

I have done the conditioning. Can the column be blocked due to conditioning? "

The answer is yes, if the condition of the column was 'so and so', and you conditioned it 'in a certain way', yes, it is possible to damage a mole sieve column in this manner. But your case would be extreme, but not impossible.

Good luck,

Rod