What Analytical Labs Need to Know About Nitrosamines
Updated · CATO technical documentation
Few classes of impurity have changed routine pharmaceutical testing as quickly as the nitrosamines. The sartan recalls, followed by findings in ranitidine and metformin, forced manufacturers and testing laboratories to re-examine how these impurities form, how they are detected, and how their presence is controlled. Both the FDA and the EMA have published guidance on nitrosamine impurities, and the expectation is now a routine, documented risk assessment rather than a one-off campaign. For an analytical laboratory the practical questions are narrower: which methods are fit for purpose, what documentation is expected, and which steps in a nitrosamine method fail most often. This guide is part of our guides library.
Why nitrosamines are regulated differently
Nitrosamines are treated as a cohort of concern. Under the ICH M7 framework for mutagenic impurities, most mutagenic impurities can be controlled against a generic threshold of toxicological concern; nitrosamines are handled more conservatively, generally with compound-specific limits set by the relevant regulator. That distinction drives everything downstream.
It means two things for the laboratory. First, results are judged against the applicable regulatory limit for the specific nitrosamine, not against a generic limit of detection target, so the method must be sensitive enough for that value and the reporting format must make the comparison explicit. Second, absence is not assumed. A negative result on one batch does not remove the need for a risk assessment covering the route of synthesis, the suppliers of starting materials, and the equipment used.
Where nitrosamines come from
Formation generally requires two things to meet: an amine, usually secondary but sometimes tertiary or quaternary, and a nitrosating species derived from nitrite or a related reagent. In practice that meeting point can occur in several places along a product's life.
- Synthesis of the drug substance, where amine-containing reagents, catalysts, or solvents are exposed to nitrosating conditions.
- Raw materials and starting materials, including some grades of common solvents and reagents that carry amine impurities.
- Recovered solvents and reused materials, where trace contamination accumulates across cycles.
- Water and utilities used in processing.
- Rubber components such as seals, gaskets, stoppers, and gaskets in equipment, which can leach amine precursors.
- Excipients, primary packaging, and the drug product itself, either as a carry-over or through degradation of the active substance during storage.
Nitrosamine drug substance-related impurities, often abbreviated NDSRIs, are a distinct case. Here the nitrosamine retains most of the parent drug structure, which makes the molecule larger, less volatile, and often thermally labile. That difference determines the analytical approach.
How laboratories detect and quantify them
Method selection follows volatility. Small, volatile nitrosamines such as NDMA and NDEA are usually determined by gas chromatography with tandem mass spectrometry, frequently with a headspace or large-volume injection step. Non-volatile NDSRIs are generally determined by liquid chromatography with tandem mass spectrometry, typically with electrospray ionisation.
The choice is not free. Some NDSRIs fragment or rearrange in a hot GC inlet, so a GC method that works for NDMA may be unsuitable for a larger analogue; conversely, an LC method must solve the ionisation and matrix problems that a simpler volatile analyte does not present. Confirmatory analysis, where a first-line result is verified by a second, independent technique, is common practice for out-of-specification or borderline findings.
Three operational details decide whether a nitrosamine method survives contact with routine samples.
- Sample preparation must not create the analyte. Nitrite-containing reagents, acidic conditions, and some rubber or plastic labware can generate nitrosamines from amine-containing samples; use inert, well-cleaned glassware and reagent blanks that prove the point.
- Carryover must be controlled and demonstrated. These analytes are potent and methods run at low concentrations, so injection sequence and wash steps matter as much as the calibration curve.
- Quantification needs a reliable anchor. Native standards define retention and response, while stable isotope-labelled internal standards correct for recovery and matrix effects. CATO supplies both native and deuterated nitrosamine standards — for example N-nitrosodimethylamine-d6 (CAS 17829-05-9) — through our product range, and the isotope-labelled standards guide covers when a labelled analogue justifies its own specification.
Validation follows the usual expectations for a quantitative impurity method, covering specificity, linearity, accuracy, precision, and limits of detection and quantitation. Given the low concentrations involved, the limit of quantitation should be shown to sit below the applicable regulatory limit with margin.
Practical checklist
- Map every amine input and every nitrosating opportunity across the route, including suppliers and recovered materials.
- Confirm the method is validated at the concentration range that matters for the compound-specific limit.
- Run reagent and labware blanks alongside every batch series.
- Include an isotope-labelled internal standard where matrix effects or recovery are variable.
- Document carryover evaluation and set the injection sequence accordingly.
- Verify the identity of any reference standard used, and keep its characterisation data with the raw data. A certificate from a supplier such as CATO will state identity, purity, content basis, and storage conditions; see how to read a certificate of analysis and our quality documentation.
- Re-test after any change of API supplier, solvent source, or equipment, since these changes can shift the risk profile.
Request a quote
For nitrosamine and NDSRI standards, send the CAS number or the parent drug name, the impurity structure where known, and the concentration range you need to cover to [email protected], or use the contact page. CATO supplies nitrosamine-related impurity standards together with the identity and purity documentation your method file will need, and can advise on available formats. All such materials are supplied for laboratory and research use only.