Dear members,
I have two questions about my work,
1)If is there competition to product adduct H+or Na+?
2)Why the TIC peak after column dissapeared comparing with directly flow injecting ? what factors should I consider to solve this question?
Thank you in advance.
Michelle

To answer the first question: There is competition between the formation of H+ and Na+. Increasing source CID or temperature can shift formation toward M+H+ and away from Na+ or other adducts. (Adducts form under lower energy conditions.)
I am a little unclear about the second question. Are you saying that you don't see any peak corresponding to your analyte? Or are you saying that M+H+ disappears?

Dear Anonymous,
I can describe in detail. I run a sample through the column firstly and there is no any TIC peak in the chromatograph and any corresponding Mass spctra. Then I injected the sample to Mass directly, Mass gave me some information same with my expection. My collegue said this result was due to diffusion in column and flow. I cann't agree with her.
So could you give me more direction?

Dear Anonymous,
I can describe in detail. I run a sample through the column firstly and there is no any TIC peak in the chromatograph and any corresponding Mass spctra. Then I injected the sample to Mass directly, Mass gave me some information same with my expection. My collegue said this result was due to diffusion in column and flow. I cann't agree with her.
So could you give me more direction?

Are you sure that your analyte is eluting from the column? What is your mobile phase? When you inject the sample into the MS, and you using mobile phase at a flow equivalent to the flow from your column, or is it just the analyte and solvent?

Yes, I am sure. I just inject the sample to MS directly during the same run as injecting to LC.
No any condition was changed. I use Waters 2695-ZQ.And the sample is ionic sample so I think it could be elunt between 30 min.
Any comment?Thank you.

Hi Michelle,

If I understand well, in flow injection analysis (FIA) where you injected your sample without column, you observe a [M+Na]+ ion as the major ion; which desappears when you inject in your LC column before detection with the MS.

My first guess is that when you are doing FIA, you have plenty of Na+ available to create adducts, that is why you see your [M+Na]+. In the LC version (and assuming that your compound of interest is retained a little bit) most of the Na+ will be eluted in the hold up time, so when your analyte is eluted it has not enough Na to form the adduct and maybe the [M+H] is your major peak (or maybe you see nothing because your compounds is not easily ionisable).

Hope the above helps,

Kostas

Is your method isocratic? If this is the case, how do you know that your compound elutes from the column? Do you only think it elutes?

Thank you, Kostas, however, you give me
a direction to identify the cause.
And Anonymous: I run my sample isocratic. The sample is easy to ionize so I think it should be elute in thirty minuts.
I will post my continuos observation, pls give me more in future.
Michelle

I bet that you problem is that the compound either does not elute under your isocratic conditions or that the peak is so wide that you do not recognize it as a peak. Try a gradient and see if you still dont find your peak.