varian 450GC/240MS

[sundaresan]

Hello,

I'd like to know more details regarding air/water level in 240 MS.Although instrument shows that both air and water level are in acceptable level,ie regarding 19/18 ratio and what is the acceptable value.

And how should i perform preventive maintainence for 240 MS?

Your reply is apprecieated.

sundaresan.

[/b]

[mabrouk mahmoud]

1/Width of m/z 28 at 10% Peak Height<1u, Ratio 19/18 <20%: the both air (N2) and water (19/18) are in acceptable leval.
2/Width of m/z 28 at 10% Peak Height<1.8u, Ratio 19/18 <50%: the both air (N2) and water (19/18) are in acceptable leval, but ther are a small leak.
3/Width of m/z 28 at 10% Peak Height<3.1u, Ratio 19/18 <91%: there are a senificant leak in the system (air and water).
4/Width of m/z 28 at 10% Peak Height>3.1u, Ratio 19/18 >91%: there are a massive leak in the system (air and water).
the software indicate "the both air (N2) and water (19/18) are in acceptable leval" if there are the values of conditions 1 or 2 when you make the test of air water.
the software indicate "there are in elivate air and water in the system.
if there are the values of condition 3 or 4 when you make the test of air water.
Wat's the configuration of your system: external or internal?

[sundaresan]

Hi,

We have varain 450 GC coupled with 240MS Which has ion trap mass analyzer, Internal ionization.

I would like to clarify regarding 240MS Air/Water check.

The water level in the system is at "Elevated level". Mass 19/18 ratio is around 52% keeps fluctuating between 50 -60%

We did some routine and preventive maintenance to get rid of this.

We changed roughing pump oil,septa, Injector liner, Made a leak test with 1:1 Isopropanol and water. Baked out system after maintenance for 18 hours.

But the water level hasn't come down to acceptable level, Some time its not stable it shows its in acceptable level, Again the status message is change to elevated level.

Any suggestions are apprecieated

Thanks and regards,

R.Sundaresan

[Hornet]

Hi,

We have varain 450 GC coupled with 240MS Which has ion trap mass analyzer, Internal ionization.

I would like to clarify regarding 240MS Air/Water check.

The water level in the system is at "Elevated level". Mass 19/18 ratio is around 52% keeps fluctuating between 50 -60%

We did some routine and preventive maintenance to get rid of this.

We changed roughing pump oil,septa, Injector liner, Made a leak test with 1:1 Isopropanol and water. Baked out system after maintenance for 18 hours.

But the water level hasn't come down to acceptable level, Some time its not stable it shows its in acceptable level, Again the status message is change to elevated level.

Any suggestions are apprecieated

Thanks and regards,

R.Sundaresan

First, baking out for so long with air/water in the system is the best way to destroy your column, never do it again.
I can try to help you but i need some informations:
- before the bakeout you had both air and water at high concentrations in the system and after the bake out you have only high water level, this is what i understand from your posts, is it correct? If it's like this it sounds a bit weird to me, usually after bakeout the water level goes down to a mid/acceptable level even if there is a small to moderate leak, while the air level stays high. Please explain better this part.
- i need to know what is your injector model, is it a Varian 1177 split/splitless or a varian 1079? If it is a 1177, which o-rings are you using?
- where have you done the 2-propanol leak test? Just at column ends or somewhere else?

[sundaresan]

Thanks for your reply,

In our system the Air level is at accepatable level, Only the water level is not stable.

Since we baked out the 240 MS system several times,But we kept GC column oven at 100c. During the bakeout. Still water level is not at acceptable level. I guess we don't have a leak the mass width of peak 28 should be above 1 M/Z if there is a air leak. But the mass 28 peak width is around 0.70 m/z ratio. So its within the range.

We did iso propanol and water in 1:1 ratio leak test only on the GC Plumbing fittings, Column ends and gas inlet.

Our injector type is 1177 Split/split less injector. We replaced the injector port with new septa and glass insert.

[Hornet]

Thanks for your reply,

In our system the Air level is at accepatable level, Only the water level is not stable.

Since we baked out the 240 MS system several times,But we kept GC column oven at 100c. During the bakeout. Still water level is not at acceptable level. I guess we don't have a leak the mass width of peak 28 should be above 1 M/Z if there is a air leak. But the mass 28 peak width is around 0.70 m/z ratio. So its within the range.

We did iso propanol and water in 1:1 ratio leak test only on the GC Plumbing fittings, Column ends and gas inlet.

Our injector type is 1177 Split/split less injector. We replaced the injector port with new septa and glass insert.

It sounds like your problem is in the GC, it's impossible that the trap at high temperatures didn't remove the water after that bakeout.
With your injector the critical points for leak are injector end of column, transferline and the o-ring of the injector.
After you change the liner, put a new oring and turn the 2 little screws on top of it, try a leak check at the oring, it's VERY easy for it to leak, especially if you use graphite orings (of course do the check after you have put the septum and the inj nut in position).

If you are fine on both column ends and inlet, that it's either gas contamination (have you checked the air/water trap conditions?) or some o-rings at the CI or calgas valve. I highly doubt there is a leak at the spectrometer, because a leak there would mean your turbo isn't even at full speed.

[sundaresan]

Ya your right, But since we did HMN Noise test its 25000. So these confirms that trap is clean completely. Since we are using 1177 Split/Splitless injector its simple to change the glass insert that we did during our routine maintenance.
The possible cause for the water level in the system is the carrier gas itself although we are using research grade (99.9999% purity)

We confirmed the above cause by disabling the constant pressure of Carrier gas, ie we changed the inlet pressure manually from the GC

Then we monitored the Air/Water check, As inlet pressure raised the water level is also drifted rapidly. Again we resumed to constant flow the water level was down. So use ultra high purity(99.9999%) helium gas. Also while procuring the gas ask for Quality control certificate.

[Hornet]

Glad to see you found the problem. Try using Agilent gas clean filter (trap for O2 and water) model CP17973 or old Varian ones if someone still sells those. I don't know if restek or other sellers produce these filters, ask around for better prices.
Anyway if the gas quality sucks your filters will get ruined very fast, i had to fight with some bad gas sellers in the past because they make chromatographers lose money and time, speak to them about your helium.

GL

[sundaresan]

Thanks mate,

Ya we are using the agilent gas clean filter as you mentioned, Still we are using the same helium gas tank, Connected with two to three moisture and hydrocarbon filters, It may saturate after sometime. Since we have to finish the existing gas tank. To replace new one with ultra high purity.

Hope we will get the right helium carrier gas next time.

Appreciate your assistance

Regards,
R.Sundaresan