Hi everybody

I am using Acetonitrile and water as solvent in one of the methods i am developing. The problem is that i am getting a negative dip at the time of one of the impurities. I either want to move the impurity which is a sulfonamide of the drug and hence very polar (Any approaches???)Can I add something to the solvent or to the mobile phase??? or I want to change the solvent which infact I tried doing but methanol and water combination also seemed to be giving the same negative dip. The Tetrahydrofuran gives a positive peak at that time.

It is really urgent can someone help???

Thanks

Sean

Use an ammonium formate/formic acid buffer with a gradient. You also might try switching to methanol or 50/50 methanol/acetonitrile. For more detail, read
Lindsey et al. "Analysis of Trace levels of sulfonamide and tetracycline antimicrobials in ground water and surface water using solid-phase extraction and liquid chromatography/mass spectrometry." Anal. Chem. 2001, 73, 4640-4646.

Also, be sure to put the sulfonamide in a solution as close to your starting mobile phase as possible to ensure the best peak shape.