Does anyone have experience with unstable standard of nitrosamine in solid state?
We have an issue with standard that is stable in solution not more than 1 hour, whereas there is no conclusive data for the stability in solid state. The standard belongs to the group of other N-nitroso structures with a limit of 1500 ng/day.
Also, because of the instability of the molecule, during the confirmatory analysis we cannot be sure about the quantification of the impurity, whether the impurity degrades in the solution during sample preparation or it is not formed at all.
How should the risk assessment be performed in cases like this? Is there another option to present the risk analysis without confirmatory analysis?
We had a similar situation, where the standard as stable in solid state (we ask for stability studies to the spplier) but in solution was quite unstable in the usual organic solvents and acid pH.
We then change the wy the we prepared the solution. We prepare only in acetonitrile (that is less reactive that water or methanol). All solutions were store immediatly after preparation and were separated into individual vials or flask that only use once. The storage temperature was -18ºC.
We perform all the extrations at the lowest temperature possible (extraction, centrifugation, ultrasounds batch, etc.) in the lab and without light interference.
It took more of work than usual to this project, but we were able to keep stability and good recoveries during confirmatory testing.
Exactly, if you can share the structure, it will be easier to determine its stability/reactivity. On the other hand, it is logical that a good number of compounds included in the group of other N-nitroso structures are unstable if they can be synthesized. It will depend on whether it is an aromatic compound or its chemical environment.
From my point of view, the synthesis of this nitrosamine is not trivial and, if obtained, there is a risk that it may be unstable, hence the problem you have with the standard.
You should request the complete characterization of the standard, including the experiments mentioned by Christos.
I have some experience with Nitroso-Tadalafil, and yes I can confirm that it converts to tadalafil. The use of acetonitrile as solvent helps to stabilize the molecule and working at low temperatures also helps. The use of any acids will convert the molecule in tadalafil. The molecule is quite tricky as it converts in solution and in chromatography due to the proprieties. So the use of mobile phases with on acid addition and with acetonitrile will help you. The use of methanol in mobile phase or in extraction steps will accelerate the degradation of nitroso-tadalafil.
I recommend to use as much acetonitrile as possible. From the tests that I did, the solution can be stable in 50:50 water:acetonitrile, but at low temperatures. Because when I development the time was short I was not able to study the stability as I wanted, but the solutions were stable at low temperature in acetonitrile for about 12-24H.
if I may intervene, I see that community’s attention and interest is increasing in relation to Nitroso-compound. I wonder if this is driven by regulatory requirements.
Thank you very much for the discussions, we are currently trying the recommended experiments and will get back with the results.
@elenipoliti The impurity is listed in Appendix 1 from Q&A under “other N-nitroso structures”. According to the guideline, since the impurity is listed and if it is available, the same should be included in a risk assessment and supported by confirmatory testing. Our concern was that if the reference standard in not stable, are we liberated from confirmatory analysis, since according to Q&A if the standard cannot be synthetized, that confirmatory analysis is not required.
Currently we are doubting the stability of the reference standard that is in solid state. We have obtained it from two vendors, they both had it synthetized 4-5 months before the delivery arrived. The standard may have been stable for a shorter period, but we do not have evidence that the standard is not degraded, since we cannot detect it in the samples that we have received.
We will try the experiments that are suggested in this group and in @N nitroso tadalafil and will get back.
From what I learned the nitroso-tadalafil is stable in solid state but in solution can be quite tricky to be stabilized (I recommend acetonitrile as solvent and low temperature storage).
