Hi Mouna Derdour!

What are the percentages of Water, Oxygen, Nitrogen? What are the ratios to the peak with m/z = 69?

Hi Mouna,

Do you mean that the H20 peak is more intense than the N2 and O2 peaks from air?You will always get a small air and water background from leaks etc. Water tends to be absorbed onto the stainless steel surfaces of a mass spectrometer, and will be desorbed when the surfaces warm when the instrument is turned on.  

A likely source of water is from your GC carrier gas - It might be worth checking your gas line filter. Or you might be injecting water with your sample? You can also get a lot of water from breakdown products of a heavily contaminated or dirty injection port liner, or a degraded GC column.

If the carrier gas is OK, you could have an air leak. An easy way to locate a leak is to use argon gas  - I normally connect a plastic tube to a regulated argon gas line. A flow of ~50mL a minute is OK. Move the end of the tube around likely leak sites and look for a sudden increase in the 40 au ion (1% of air is argon, so you will always see it). A good places to start is where the GC column enters the mass spectrometer, the ferrule often shrinks with use causing a leak.

Regards, Tim

I agree with Tim. Please check all the possible leak points with Ar gas.  If leak is not detected, then one possibility is the carrier gas. Hope you are using a moisture trap ( self indicating silica + molecular sieve). It is a good idea to regenerate the moisture trap in case you were using it for a long time. If your carrier gas is helium, then any outside air leak into the system can be immediately detected by a high intensity 28 ion. Regards,

Girijan Menon 

Hello

  The percentage of moisture is too high and I can not get to settle it because every time I made the tunning the percentage decreasing to 57%(H2O) and when I run the tune again it increases to 80%.

Attached you will find the tune report.

Regards.Mouna

Hi Mouna,

What did you do between the first tuning und the second tuning?

Are all temperatures ok? If you have changed the column or vented the system, the column often needs to be heated to evaporate the water entering the column during cooling and venting. The peak for water then rises again.

Could you please attach the tune report again?

Konrad

I'm sorry you find attached the tune report

hi Konrad Neumann 

between the two tune I've done nothing I injected 15 sample olive oil (methyl ester) and just the next day I did the tune I note the high percentage of humidity

the tune should be done every day before injecting according to Agilent engineer

Mouna

Hi Mouna!

I wonder why the the peak with 219 has a higher intensity as the peak 69. This is unusual for me. But I think it does not matter so far.

The percentage for water is ca. 45%. The value of 73,8% is the fraction of water of the sum of water, nitrogen, oxygen, argon and CO2 I guess. So maybe oxygen, nitrogen and argon are decreasing and water remains constant. Could you please attach a tuning report with the other water percentage?

Is the percentage of water now constant? And if not can you estimate the rate of fluctuation?

Greetings, Konrad

It appears that the water came from your samples, depending on how you generated the olive oil methyl esters a by-product of the reaction could be water. The solvent you are dissolving the samples in could also be wet. How much olive oil are you injecting, and what solvent are you injecting the olive oil in?

Hello thank you all for your help

The olive oil samples that I injected are dissolved in hexane I have already worked with the same samples and the same solvent and any problems are detected

Konrad Neumann the percentage of water is not constant ,could you please explained how you extract 45% of water . The gas used by the equipment is helium connected to gas filter.

Tim Strutt please could you explain me more your method of detection the air leak

How old is the septum on the injector? It might need to be replaced. Also check the age on the absorbent capsule on the gas purge for the injector.  My past lab worked with olive oil and the injector vent lines were very prone to fouling and clogging. Is the injector liner intact?

All the suggestions so far are worth considering.  Another possibility is that the nut connecting the GC column to the transfer line has worked loose with the thermal cycling of the oven.  You should pick this up with one of the earlier suggestions to leak test the system with argon.  Agilent sell a special nut with an internal spring to prevent this happening.

If all this does not help, you can also use a blind plug for the MS to uncouple the GC. Then you can see if this phenomenon disappears (the problem is located at the GC (column coupling to MS or injector, gas support, etc.) or remains (the problem is on the MS-side)).

If the problem is onthe GC side you can manipulate the gas flows and try to locate it. E.g. if setting the column flow higher and the water content rises, there is water in the carrier gas. If it first rises and then decreases there is a leak somewhere else.Test it with argon or something else (like pentane (fragments 57, 42 and 29)).

But not all parts of the GC are accessible with argon. There are parts at the injector block you will have to disassemble because there are under the thermo-insulation.

Dear Mouna ,

Do you see high levels of 28 and 32 (air)? If you do, then there is a leak in the system. But, if mass 28 and 32 are normal and not too high and you haven't cleaned the source recently, also the level of 18 is more or less stable then, more likely it is the carrier gas that has high level of water.

Hello everyone

thank you for your help, I was able to set the percentage of oxygen and nitrogen after having changed the gas filter

Best regards

hello,

Today I have another problem because after the adjustment of the percentage of H2O N2 percentage is increased up to 32% and I don't  know the source of this problem. is there someone who can explain the cause.please

Thank you

Hi!

Could you please send a picture of the tune Report?

Greetings! 

I changed the gas bottle and tried again to calibrate the equipment but no improvement

Hi!

To me it looks as if there is a leakage or remainig air. The ratio of N2 and O2 ist 3.7. This is the same as it is in air. I dont know how the tuning program calculates the percentage of N2, O2, Water and CO2. But 28.9 / 7.9  = 78 / 21 = 3.7. Do you have the peak for Argon (40)?

I agree with Konrad - you either have a leak (gently tighten nuts holding the column. Do you have a new septum in place?) or you are looking at the outgassing of residual gas during pump down.  If the latter it should decrease to normal after a couple of hours.

Hello

the percentage of N2 is slightly decreased but still high 19-20%, however I changed the septum, liner, and even the gas bottle and I tightened nuts holding the column

in your opinion what's the problem?

Greetings

You have a leak.

As has already been suggested; isolate the GC from the MS by removing the column from the transfer line and plugging the connection. If you still have high levels of nitrogen the leak is in the MS. If the levels go down it is in the GC or the upstream plumbing.

If the leak is in the GC, check the GC inlet and all the gas supply piping to the GC with a leak seeker. Do not use bubble liquids for this, they will contaminate the system. 

Simply tightening nuts without locating leaks is bad practice - if you have a cracked or distorted ferrule tightening the nut will make the problem worse.

The ratio of N2 to O2 is konstant at ca. 4?

In your situation I would first check for leaks at the pressure reducing valve of the gas bottle. If you have Leak Detective (eg. Restek) or something else it is quite easy otherwise you have to shut down the MS and close the needle valve. There should be no pressure drop over night or a few hours if tight. If there is a pressure drop you have a leak between bottle and pressure reducing valve. The next step is to open the needle valve and close the plug to the gas line. There also should be no pressure drop.

If this does not help you could blind plug the injector close the purge and split vent and set the GC under pressure (refer to the manual). When you stop the flow there should be no pressure drop. Otherwise there is a leak. There are many more nuts that could be leaky: Difficult is the connection between column connector and injector because it is hidden beneath the thermal insulation.

In the last step, with an equlibrated MS, you can use a bottle of Argon to check the connection from column to MS (watch m/z 40), using a hose with syringe for example.

Worst case is a hair crack of the column, you can hardly locate it. In this case flooding the whole GC-Oven with Argon gas lead to an increasing peak of m/z 40 if all other potential leaks are tight.

Good Luck!

can you please explain more how i can plugging the connection ?

Thank you

All the above answers/ suggestions are excellent...but i still want to emphasize that you go about it systematically. First start with the connecting tube to and from the regulator, followed by  injection port down to the column (inlet - to GC and oulet - to MS) using a leak detector.

To plug the connection to the transfer line you ideally need a ferrule with no hole in it. If you do not have one of those then use an ordinary ferrule with a short piece of wire in place of the column, or, third choice, a short piece of column with the end that is in the GC oven stuck into an inlet septum.

hello

hello, I have found the problem causing the high percentage of N2 because after complete verification for the third time I have found that the inlet side ferulle was stuck in the column nut I changed the column nut and ferrule and the problem is solved just after

thanks for everyone

Sorry, I was absent a few days. Congartulations for solving your Problems!

Thank you  very much Konrad Neumann

Hi, you may bake your instruments for longer period of time. You may tighten the nut of your column. You may change septum with new one. I hope this will solve your Moisture issue .

You have mentioned that water intensity is more in your MSD. After you start your GCMS and get the required level of vacuum, do a leak test. In any vacuum system 100% removal of water vapour is difficult. If your GCMS system has no leak, then the intensity of N2 (28 mass no) should be less than the intensity of water(18 mass no). Hence in a leakproof GCMS system you will always find a larger intensity for water than nitrogen.

If ceramic parts exposed to water it takes forever to remove water from the porous surface of ceramic parts.

Therefore try to bake overnight for few nights. Moving forward , for cleaning the ceramic parts use oven to clean them by burning the organic deposits rather than

using water.

If ceramic parts exposed to water it takes for ever to remove water from the porous surface of ceramic.

Therefore try to bake overnight for few nights. Moving forward , for cleaning the ceramic parts use oven to clean them by burning the organic deposits rather than using water.

If ceramic parts exposed to water it takes for ever to remove water from the porous surface of ceramic parts.

Therefore try to bake overnight for few nights. Moving forward , for cleaning the ceramic parts use oven to clean them by burning the organic deposits rather than using water.