Chromatography Forum

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

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.

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.

You can try 20mM Ammonium Acetate.

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.

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.

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.

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)