Chromatography Forum

what is the difference between related substance and impurity
and what are significant related substance impurity.

my understanding is that related substacne impurities are API degradion product which can come from any step of manufactureing and more visible impurities (means high conc) are known as significant related substance impurity..

please help and try to answer it today cause i have interview tommorow

Someone with direct regulatory experience may be able to cite a distinction, but I've never been able to see a difference. I suspect that "related substances" started as a euphemism ("our product is free from impurities . . . but it does have some related substances")

I was this questions once in inteveiw and my answer was related substance are api degradation products or other impurites are synthetic impurities which in my understand comes from the different things used in reactions like reagent ,solvent residue and all ....he was not happy with my answer so i am not sure what should i answer if i am asked this time too

Dear MK 12
Best luck for your interview
It is not necessary to have answer of all asked questions
Mostly your sincerity about work and attitude matters
Coming to point...........I think you had been asked difference between Related compounds and Purity not impurity!!!
Related compounds means all known and unknown impurities are quantified against respective standards while Purity mens substracting all the impurities whatever value remains that is purity,
generally is done by area normalisationm method in HPLC

Thanks for your reply...but what he said the all related substance are impurity but all impurities are not related substance so what did he mean by other impurities which are not related substance my answers was other impurities may be reagent imp used in reaction which are not structruclly related to API or any other contamination..anyway i hope i wont be asked same question everytime I just wanted to clear my doubts

Probably other impurities my be unknown impurities and related substances my be all known impurities whether from process, raw materials or degradation impurities

Impurity: something that is there as a result of the chemistry involved in making the product. Impurities should generally be a constant over time - some batch to batch variation will exist.

Related substance: something that is there as a result of the stability (or lack thereof) of the product. Depending on storage conditions and exposure to other chemicals, these will generally start out at zero levels and grow over time.

That's how they're generally distinguished where I work.

Related substance and impurities are same but u can devide them in
1 process impurity
2 degredent.

The "Related Substance" word is coined by European Pharnacopoeia and is confusing if we look at it in isolation. EP has defined it as,

"Related substances are known impurities which may be identified or unidentified. They include intermediates and by-products from synthetically produced organic substance,co-extreacted substances from natural products and degradation products of the substance. This definition does not include residual solvent, water, inorganic impurities, residues from cells and micro-organism or culture media used in a fermentation process."

It is correct to say that all related substance is impurity but all impurities are not related substance.

Simple words but different meaning between FDA, ICH, EP, USP. We always follow the same nomenclature, as is the norm with particular agency/market.


JM