Chromatography Forum

I did not see any peak and even not noise. I scan 50 to 500amu. What do you think? Thank a lot for your help.

I assume the instrument tunes and gives a good tune report - and at a good detector voltage? (If not - mass spec issue)

Start with a higher concentration of OFN. It is possible that the OFN is lost along the way. A higher level of sample will ensure that you see something - adn can estimate what it takes to see 1 pg. (You are running splitless on a new, clean liner and column and chromatographic conditions as were used on showing the instrument met specifications on installation?)

I used fresh standard from sigma pre-prepared. I am also running splitless mode, new, clean liner.

I assume the instrument tunes and gives a good tune report - and at a good detector voltage? (If not - mass spec issue)

Start with a higher concentration of OFN. It is possible that the OFN is lost along the way. A higher level of sample will ensure that you see something - adn can estimate what it takes to see 1 pg. (You are running splitless on a new, clean liner and column and chromatographic conditions as were used on showing the instrument met specifications on installation?)

I did not see any peak and even not noise. I scan 50 to 500amu. What do you think? Thank a lot for your help.

If the instrument is set up properly and all the settings are correct, and you are not even seeing noise then there is something seriously wrong - serious enough to need a service call I should think.

Peter

Backing up a bit - can you see anything on the injection of any kind of sample? If you can get a good tune but can not see anything in the mass spec, there is a failure of the GC to deliver a sample to the ion source. Check for a broken column (even inside the transfer line) or a plugged column. If you pull the column from the transfer line and have pressure on the column in the inlet, you should be able to dip the end of the column below the surface of solvent in one of the syringe wash vials and see a stream of bubbles coming from the column. No bubbles - no flow. Why the syringe wash vials? They are easy to see a stream of bubbles and the columns are wetted with a solvent which quickly evaporates rather than water, which you don't want to put into your mass spec.

Assuming that you can get peaks in a chromatogram, check all your settings. If you see no noise, have you set the noise threshold too high - cutting off all the noise (and small peaks).

On a scanning instrument, wider mass range decreases sensitivity. Are you using the conditions that were used when the instrument was installed? Also in a signal to noise test, the peak width is important. If you use a column with a different stationary phase, or dimensions - including film thickness, you can broaden the peak. And if the peak for testing the instrument is at the limit of what the instrument can see under optimum conditions - at less than optimum conditions, the peak will disappear. So the question about instrument configuration and conditions is a very important question.

Second - if you are purchasing the standard at the low level for demonstrating sensitivity - get another solution with a concentration at least 100 times as concentrated. I have seen where that larger peak has helped to located the correct position for the signal (hard to measure if you are looking in the wrong place) and has allowed the instrument to be optimized (such as detector voltage tweaked) and even identified a need for maintenance. In an instrument that uses HCB as the test compound – the peak for HCB at a concentration high enough to see the compound (well above that used for demonstrating specification) showed notable asymmetry. A change of chromatographic column and the instrument showed perfect performance (and met specification with flying colors).

thanks for your great explanation. I check the threshold setting in GCMS method. The threshold is too high. I think that is the reason why I did not see anything.

Backing up a bit - can you see anything on the injection of any kind of sample? If you can get a good tune but can not see anything in the mass spec, there is a failure of the GC to deliver a sample to the ion source. Check for a broken column (even inside the transfer line) or a plugged column. If you pull the column from the transfer line and have pressure on the column in the inlet, you should be able to dip the end of the column below the surface of solvent in one of the syringe wash vials and see a stream of bubbles coming from the column. No bubbles - no flow. Why the syringe wash vials? They are easy to see a stream of bubbles and the columns are wetted with a solvent which quickly evaporates rather than water, which you don't want to put into your mass spec.

Assuming that you can get peaks in a chromatogram, check all your settings. If you see no noise, have you set the noise threshold too high - cutting off all the noise (and small peaks).

On a scanning instrument, wider mass range decreases sensitivity. Are you using the conditions that were used when the instrument was installed? Also in a signal to noise test, the peak width is important. If you use a column with a different stationary phase, or dimensions - including film thickness, you can broaden the peak. And if the peak for testing the instrument is at the limit of what the instrument can see under optimum conditions - at less than optimum conditions, the peak will disappear. So the question about instrument configuration and conditions is a very important question.

Second - if you are purchasing the standard at the low level for demonstrating sensitivity - get another solution with a concentration at least 100 times as concentrated. I have seen where that larger peak has helped to located the correct position for the signal (hard to measure if you are looking in the wrong place) and has allowed the instrument to be optimized (such as detector voltage tweaked) and even identified a need for maintenance. In an instrument that uses HCB as the test compound – the peak for HCB at a concentration high enough to see the compound (well above that used for demonstrating specification) showed notable asymmetry. A change of chromatographic column and the instrument showed perfect performance (and met specification with flying colors).