LC method to LC-MS method

[sjee6]

Hello Every one

I am new to this website. I have a question about a HPLC method that is compatible for LC-MS.

My HPLC method conditions

MP buffer : 5mMKP monobasic +5mM KP dibasic ( pH is 6.97)
MP : gradient buffer:ACN
column Xterra RP8 4.6x150mm 3.5 u column

During the analysis we found a peak that was increasing during the stability. we wanted identify that peak so that we can qualify.

I was asked to develop and LC/MS compatible method.

which MP buffer i can use that is compatible with MS at pH 6.5-7

what are the parameters i should consider

thanks

[Noser222]

You could try ammonium bicarbonate, but first you might use a more typical 0.1% formic or acetic acid mobile phase and see how your sample looks.

[Uwe Neue]

It depends on how long you need the MS. I have used ammonium phosphate at pH 7 on a Z-spray interface for an extended period of time. If you will be using the method just to identify the unknown, I would use a 5 mM ammonium phosphate buffer at the same pH. It is faster than redeveloping the method.

Unfortunately, there are no true MS-compatible buffers available at pH 7. For a short period of time I was hopeful about ammonium bicarbonate at pH 7 (created by adding formic acid), but it changes pH over time. The time frame is too short to make this idea really useful.

[Bryan Evans]

You can try 20mM Ammonium Acetate.

[KC]

First of all I would listen to noser222 and see what you have with 0.1% formic and ACN. See if you can eliminate the buffer. If you must, try ammonium acetate or ammonium formate buffer. May use phosphate buffer with LC but never with LCMS.

[Uwe Neue]

KC: Never say never...
I have used ammonium phosphate pH 7 for an extended period of time using LC/MS. In the case of sjee6, it depends what is more work. It is very likely that it will require some amount of work to redevelop the method with a completely MS compatible mobile phase. On the other hand, a switch from potassium phosphate to ammonium phosphate at the same pH is not likely to affect the separation a lot. On the other hand, it may require that the interface may need to be cleaned a bit earlier than normal. It all depends on which is more work, but never is not a good answer.

[KC]

not concerned about separation or the hplc system. Don't like phosphate buffers in the mass spec ion source. I have never seen in instance where I could not find something else.

[SIELC_Tech]

sjee6,

What you are analyzing (neutral, acidic, basic or zwitter-ionic compounds)? Why do you need a buffer with pH of 7? Have you tried more firendly buffers at pH=3-5 (ammonium formate, amonium acetate)