N-Nitroso Metamizole Impurity C

Confirmatory Testing & Analytical Challenges
1

Hello everyone,

I had being develop a method of N-nitroso Metamizole Impurity C using LC-MS. And have some issue as below :

  1. N-Nitroso Metamizole Impurity C peak is appears in diluent chromatogram (even tried to minimize contamination like using new glassware and vials, first and freah prepare of solvent (before taking reference standard), and using some of column (stationary phase))
  2. N-nitroso Metamizole Impurity C peak is drifting (not come back baseline to baseline, so the peak is difficult to cut by integration automatic)

We using methanol as diluent, and mobile phase using mixture of formic acid and methanol, and then rinsing injector using 2%DMSO in methanol.

Anyone have same issue?

Thank you

2

What Stationary Phase are you using ? We did not have an issues with drifting RTs.

However what we discovered is, that the Metamizole itself was undergoing on column formation of the nitrosamine, depending on the eluents used.

Acetonitrile was better and also we used an really small amount of formic acid. Not the typical 0.1%.. I would really try to avoid methanol for Metamizole as much as possible.

3

We using Biphenyl as stationary phase and using 0.05% formic acid as mobile phase A.

We tried Acetonitrile as diluent and mobile phase B, however the peak of N-Nitroso Metamizole is not far apart from Metamizole peak and make the peak form is not like a peak (wide peak tip).