how regenerate the Molecular sieve column

[arfeen66]

hi i am new in this forum i am facing a problem in my gas sample in Varian-450-GC as there is no separation of methane & co peaks, there is only one peak

[Consumer Products Guy]

When we used to do this type of assay with packed molecular sieve columns: If the separation between 02 and N2 is not good, regenerate the column by heating at 300C for 1/2 hour with carrier gas flowing.

[chromatographer1]

Since it appears that your column is saturated with water I would not follow the recommendation of CPG, as usually his advice is excellent, but I disagree with him in this case. I understand why he said what he said and the situation of the column about which he gave his advice. It is not appropriate for someone with a water saturated MS5A column where methane and CO do not separate. If you follow his advice the packing may become damaged beyond repair. If you read the original patents on this packing you may understand why. I consider the details to be proprietary information and will not discuss them here.

I suggest you slowly ramp your oven from an initial temperature of 40°, hold it for an hour, then 2°/min to 120°, hold it another hour, then 2°/min to 200°C and hold it overnight or at least 4 hours.

Use the fastest carrier flow rate you can afford or is convenient.

This will recover 80-90% of the separation of your column. To gain the additional 20% you will need to heat the column to 250°C overnight, but that will only increase your CO peak retention time and make that peak tail more.

best wishes,

Rodney George

[Spuzzin]

One minor addition to the above posts. Assuming you are using a Varian system similar to mine you probabaly have multiple columns in there. It's unlikely your other columns are happy at 400 Deg C (and possibly not even 250 Deg C) so either remove the other columns (which is a pain) and use copper to bridge the gaps or transfer you mol seive to another system (if you have one spare) before conditioning.

On a similar note, the 450-GC has a standby mode that allows the instrument to sit at whatever temp you want overnight. Personally I use 200 Deg C.

Good Luck

Rich

[chromatographer1]

I concur. Rich has a good point and you would do well to follow it.

Rodney George

[arfeen66]

Thanks u for valuable suggestions my column is in valve oven & maximum temperature is 220°
i will give temperature to 200° in standby method, can it cause condensation in my regular oven Column or not

[chromatographer]

I didn't realize 5A could be so delicate Is this because of the water and if it were more dry would the normal 400C temp limit and faster temp ramps be ok? I have seen references to the need for careful regeneration of mole sieves but no specifics.

[arfeen66]

thanks i will give feedback soon

[chromatographer1]

If you need a test to determine if your molecular sieve column is damaged check the symmetry of the carbon monoxide (CO) peak. If it is asymmetrical or if it tails, the packing is damaged. Anyone who wants to see an undamaged column by its CO peak, go to the Supelco web site and look up the bulletin T195890 and look on page 64.

The last peak on the right is CO.

I don't work for Supelco anymore.

best wishes,

Rodney George

[arfeen66]

there is no peak separation Even heating the column at 200°C for 8 hrs.The problem is that column is in Valve oven & i don't heat it above 200°C because of other column there is only one peak of Methane & CO but peak is
in symetry

[chromatographer1]

If you are sure the sample is actually passing through the column and that your carrier gas is dry, then get a new column. Something sounds very wrong. Did someone switch out a column without telling you?

Rodney George

[arfeen66]

i have baked the column at 190°C for 8 hrs, now the peaks r separated but sequence of peaks change from CH4,CO to CO,CH4 also the retention time decreased & peaks narrows

[chromatographer1]

Whatever column you had in your GC it is not a mole sieve column anymore.

For CO to elute before methane it would be porous polymer column, like a Porapak Q.

I think someone switched tags on your columns accidentally.

Throw away your column and quit wasting expensive time. Get a new column and take good care of it.

best wishes,

ROdney George