Area Falling

[punt]

Hi all,

The hydrogen area count in my GC is falling about 1% every 2 to 3 days. When i measure the flow from the TCD, i find the carrier flow is actually increasing gradually too. Seem like the fall in area is due to the flow increase. What kind of problems can lead to this kind of sympton?

I am injecting pure H2 and the carrier gas use is N2.
Column: Haysep combine with Molsieve5A



Thank you

[chromatographer1]

Everything sounds normal except why the flow is increasing. It may be that the column supports are drying out (not a bad thing). Or the regulation of the carrier flow is changing. Or has the temperature of the detector changed?

Just drop the flow a little to bring the response back to where it was.

Has the weather changed lately? Have you moved the GC to a higher altitude?

best wishes,

Rod

[punt]

Hi Rod,

Thanks for your reply.
The area is falling every 2 to 3 days so if lower the flow to bring the area back, then the area will still continue to drop every 2 to 3 days.
What do you mean by column support drying out? and would it cause a rise in flow? It is actually a new column.

Thank you

[chromatographer1]

First I assume you are talking about packed columns.

When the molesieve loses water content it 'dries out' and the pressure required to maintain a certain flow will decrease, so maintaining the same pressure means the flow rate will increase and the sensitivity of the analyte will decrease.

Have you conditioned these columns at 170C (HS-T, N, S) or 200C (HS-Q, A, R, D) overnight recently?

Rod

[punt]

Hi Rod,

Yah it is micropacked column.
I did not condition the column. It is a brand new column and has been pre-conditioned by the manufacturer.
So I presume when the water content totally dry out, the flow and area will be stable.
Thanks for the information.

Regards

[chromatographer1]

I would condition them separately. First the porous polymer column for 4 hours and then the MS5A column overnight, starting with a slow ramp
(1 degree per min) from 100C to 30C below temp limit for polymer column and from 100C to 220C for MS5A column.

best wishes,

Rod

[punt]

Hi All/Rod,

After installing my new column (Haysep Q / Molsieve 5A), the original profile for pure hydrogen peak i get is a Fronting peak.

1 month later, the pure Hydrogen peak in the GC change to a symmetrical Peak shape. Is it normal for this to occur for this kind of micropacked column?

Thank you

[chromatographer1]

I suspect without seeing the peaks, the peak is changing from an overloaded peak to an overloaded peak that is beginning to tail, giving a more symmetrical peak.

As the sieve column collects water this happens.

Recondition the column and see if the original conditions return.

best wishes

Rod

[punt]

Hi rod,

Thanks for your reply, the symmetrical peak does not seem to be tailing. Can i send you the picture of the chromatogram through your email?

Thank you

[chromatographer1]

Yes you may. My email is documented here in my profile.

best wishes,

Rod

[AICMM]

punt,

I think it is entirely possible that your micro-packed is getting overloaded. Quick way to test this is to install a much smaller loop and inject less and see if your peak symmetry returns. You should also be seeing a slight retention shift if you are overloading.

You might consider full blow 1/8" columns if you are shooting a lot of sample.

Best regards,

AICMM

[AICMM]

Punt,

One other thing I forgot. TCD is flow sensitive so an increase in flow rate will cause a decrease in sensitivity. You should also see a retention time shift with an increase in column flow rate. If not, then something else may be causing the flow changes. What type of instrument are you using?

Best regards,

AICMM

[punt]

Hi Rod,

I have send the chromatogram to your email.


Hi AICMM,

Actually i have 2 set of the same GC running the same hydrogen gas. One of them have remain peak fronting when i inject pure H2 since the first day of installation. (1 year ago).

The other set of GC which experience fall in area count. As suggest by Rod, it could be the water in the column is drying out. But what puzzled me is the peak change from Fronting to Symmetry. Perhaps i try lower the flow to increase area count and see if the peak change back to fronting

Both the GC configuration is the same. The column is 1/16'' and the sample loop is 1 ml.

Thank you

[chromatographer1]

Do your micropacked columns have screen terminations, glass wool, or wire bundles?

best wishes,

Rod

I got your chromatogram and replied.

[punt]

Hi Rod,

I am not sure if the micropacked column contains glasswool.
The column was customised and purchased from AC.
The column seem to be very inconsistent. 2 same column but to achieve the same flow rate, the pressure use for 1 column is 380kPa and 200KPa for another one. Vendor claim that is it due to the different amount of packing inside the column.

Is it normal for this kind of column to have such inconsistent packing material inside?

Do you know anywhere else i can purchased this kind of Haysep and molecular sieve with silco treated stainless steel column?

Thank you