Chromatography Forum

We are currently running standards of sulfonamides on LCMSMS and have the following queries. Any help on these would be much appreciated

1. Two sulfonamides Sulfadoxine and Sulfadimethoxine that have to be analysed are positional isomers. They have the same precurson ion (311) and the same product ions (156, 108, etc.). We are even getting the same retention time for both. It would not be possible to distinguish between the compounds under these conditions. Can someone suggest any alternative to this or would it be sufficient to study the transition once at the same retention time.

2. There are also some doubts regarding another sulfonamide Sulfanilamide. We have purchased the standard from Sigma Aldrich. The product ion for quantification should be (156) for the precursor ion (173) according to the literature but we are not getting this ion in abundance by all possible changes in the collsion energy and the fragmentor. Would anyone have you any idea about such behaviour of the fragmenation pattern of the compound or is there some problem with the standard we have purchased.

Thanks

1. looks like you are going to have to do the "old fashion" LC separation to get these. If you can't separate these with a gradient, try changing the pH of the buffer. Do you know the pKa's? If they differ, then adjusting the pH will solve your problem.

Maybe you need to try a different column...

I think looking into the pka's is a good idea as well.

The environment of some of those nitrogens might be different enough to be useable, either by LC or on SPE.

A good selection of Polar RP colums (amine, cyano, etc) maybe even a phenyl and some luck would be nice.

Alp

We are currently analyzing sulfonamides with a multiresidue method together with other antibiotics. Our LC method separates your two troublesome analytes, the retention time being 5.15 and 6.88 min. respectively.

The separation is performed in an Acquity UPLC system with a BEH C18 2.1 x 100 mm 1.7 um column. The mobile phases are 0.2% Oxalic acid 0.2% formic acid in water (A) and 0.2% formic acid in acetonitrile (B). The conditions are:

Initial: 8 % A, 92% B
Lineal gradient to 15% A, 85% B in 5 minutes
Lineal gradient to 55% A, 45% B in 3 minutes
Flow 0.5 ml/min.
Column temperature 45ºC

I think it should also work in a HPLC system not just in UHPLC.

Thanks guys, will try these solutions and get back with you