The guideline for DNA-reactive (mutagenic) impurities. It classifies impurities by mutagenic and carcinogenic potential and, where no compound-specific data exist, uses a threshold of toxicological concern of 1.5 µg per day for lifetime exposure.

Purity and Impurity Profiles in Pharma Raw Materials

Q: What is an impurity profile?

A description of the identified and unidentified impurities typically present in a batch of a substance, with their levels. It shows not only how pure the material is, but which other substances are present, which is what decides safety and regulatory acceptability.

Q: Why is assay alone not enough?

Two batches can both assay 99.5% and still differ in the remaining 0.5%. If one contains a mutagenic, toxic or reactive impurity, it may be unsafe or unacceptable even though its assay passes. That is why specifications list named impurities, residual solvents and elemental limits, not only purity.

Q: What are the ICH Q3A thresholds for impurities in a drug substance?

For a maximum daily dose up to 2 g, the reporting threshold is 0.05%, the identification threshold is 0.10% or 1.0 mg per day (whichever is lower), and the qualification threshold is 0.15% or 1.0 mg per day (whichever is lower). Lower thresholds apply above 2 g a day.

Q: What does ICH Q3C control?

Residual solvents. It sorts solvents into Class 1 (to be avoided, such as benzene), Class 2 (limited because of toxicity, such as methanol, toluene and DMF) and Class 3 (low toxicity, generally acceptable up to 5,000 ppm without justification).

Q: What does ICH Q3D control?

Elemental impurities, such as lead, cadmium, arsenic and mercury, and metal catalysts such as palladium and nickel. It sets permitted daily exposures and expects a risk assessment covering all sources, including raw materials, equipment and container closures.

Q: How do raw materials contribute to nitrosamine risk?

Nitrosamines form when amines meet nitrosating agents such as nitrite. Raw materials can supply either side: nitrite in excipients, amine-containing solvents such as DMF, DMAc and NMP, amine reagents and recovered solvents. Regulators expect manufacturers to assess these sources, and supplier nitrite data is increasingly requested.

Q: What changed for nitrosamines in 2026?

Reported changes include an FDA update to its NDSRI recommendations on 24 July 2026, adding API-specific entries; the EMA's revised guideline on the chemistry of active substances, finalised on 20 March 2026 and effective from 1 September 2026; and continuing updates to the EMA list of acceptable intakes.

Q: Why does a change of source or route matter?

A different route, plant or starting material can produce different impurities even at the same assay. Regulators treat a change of API source, or of a critical starting material, as a change needing assessment and often prior approval, and the user must re-evaluate the impurity profile.

Q: What should buyers ask suppliers for?

The main items are: the specification and a COA for each batch, with named impurities and methods; the original manufacturer's name and site; residual solvent, elemental impurity and nitrosamine risk statements; for excipients, nitrite data where relevant; and a commitment to notify changes of route, site or starting materials.

The short answer

The impurities in the last 0.5% are what decide acceptance

Purity tells you how much of a pharmaceutical raw material is the substance you want. The impurity profile tells you what the rest is, and that is often what decides whether the material is safe and acceptable.

Raw materials feed all four of the main ICH impurity guidelines. A change of supplier, route or site can change the profile even when the assay is the same. A batch that assays 99.5% on one source and 99.5% on another can still differ in the remaining 0.5%. One of them may carry a toxic solvent residue, a metal catalyst, a reactive excipient impurity or a mutagenic by-product.

This guide from Chelora Pharmachem, a Mumbai-based supplier of pharmaceutical ingredients, explains why impurity profiles matter and what to request from suppliers. It is written for QA, regulatory and purchasing teams at formulation and API makers in India and in export markets. If you are still choosing between grades, start with our guide to pharmaceutical vs industrial grade, then come back here for the impurity detail. The information is current to 3 November 2026.

Q3A / Q3BOrganic impurities in drug substances and products, with reporting, identification and qualification thresholds.

Q3CResidual solvents left over from synthesis and purification.

Q3DElemental impurities, such as heavy metals and catalyst residues.

M7DNA-reactive (mutagenic) impurities, including nitrosamines. Nitrosamines have had their own rules since 2018, with further updates in 2026.

Key takeawaysFive things to remember

01Assay is not enough

Two batches at the same purity can carry different impurities.

02Q3A thresholds

For doses up to 2 g/day: report at 0.05%, identify at 0.10% and qualify at 0.15%, or at 1.0 mg/day if that is lower.

03Separate limit systems

Residual solvents (Q3C), elemental impurities (Q3D) and mutagenic impurities (M7) each have their own limits.

04Nitrosamines

Regulators name nitrite in excipients and amine solvents as risk sources. The FDA and EMA updated their rules in 2026.

05Change control

Know the original manufacturer, and require notice of any change of route, site or starting material.

What is the difference between purity and an impurity profile?

Assay, or purity, is a single number: the share of the material that is the named substance. It matters for potency and yield, but it says nothing about what makes up the rest. An impurity profile describes the identified and unidentified impurities typically present in a batch, and their levels. It covers related substances from synthesis, degradation products, residual solvents, elemental impurities and, where relevant, mutagenic impurities such as nitrosamines.

In practice, the profile is the fingerprint of a particular route and plant. Two manufacturers making the same API or excipient by different routes, from different starting materials, or with different catalysts and solvents, will leave different traces behind. That is why regulators link a drug's approval to a specification that names impurities, and not only to a minimum assay. It is also why a "same purity" offer from a new source is never a like-for-like swap until the profiles have been compared.

Batch A · Source 199.5%

Specified related substance0.22%
Unspecified impurities (each < 0.05%)0.12%
Water / loss on drying0.10%
Class 3 solvent (ethanol)0.06%

Same assay, different risk

Batch B · Source 299.5%

Specified related substance0.15%
New unknown peak (above ID threshold)0.14%
Class 2 solvent residue (DMF)0.11%
Water / loss on drying0.10%

Illustrative example only. It shows how two batches with identical assay can differ in what makes up the remainder.

Assay or purity

What it tells you: How much of the material is the named substance
Why it matters: Potency and yield

Impurity profile

What it tells you: Which other substances are present, identified or not, and at what levels
Why it matters: Safety, reactivity, stability and regulatory acceptance

Specified impurity

What it tells you: An impurity listed individually with its own limit
Why it matters: Must be tested on every batch

Unspecified impurity

What it tells you: Any other impurity, limited by a general threshold
Why it matters: Controls unknowns

Residual solvents and elemental impurities

What it tells you: Process solvents and metals left in the material
Why it matters: Toxicity; covered by ICH Q3C and Q3D

Which ICH guidelines set the limits?

Four sets of International Council for Harmonisation (ICH) guidelines control impurities in medicines. Regulators including CDSCO, the US FDA and the EMA apply them, and pharmacopoeias build on them. Choose a guideline below to see what it covers and its key limits.

Q3A
Q3BOrganic impuritiesDrug substances and products

Q3CResidual solventsClasses 1, 2 and 3

Q3DElemental impuritiesPermitted daily exposures

M7Mutagenic impuritiesDNA-reactive, TTC

ICH Q3A(R2) and Q3B(R2)

Q3A covers organic impurities in new drug substances. Q3B covers degradation products in new drug products. Both set three thresholds linked to the maximum daily dose. Above the reporting threshold, the impurity must be reported. Above the identification threshold, its structure must be identified. Above the qualification threshold, its biological safety must be established at the level specified.

0.05%Reporting threshold (drug substance, dose up to 2 g/day)

0.10%Identification threshold, or 1.0 mg/day if lower

0.15%Qualification threshold, or 1.0 mg/day if lower

0.03 / 0.05%Reporting / identification and qualification above 2 g/day

Q3B uses its own dose-banded thresholds for degradation products in finished products. Organic impurities in intermediates and starting materials are not directly limited by Q3A, but they carry through. An impurity in a pharmaceutical intermediate can appear in the final API if later steps do not purge it.

Excipients are not covered by Q3A. They are covered by pharmacopoeial monographs, by Q3C and Q3D (which apply to the whole drug product) and by nitrosamine risk assessments. Excipients matter as much as APIs when a profile is assessed.

The Q3A ladder for a drug substance (dose up to 2 g/day)

Each step up the ladder adds work: more reporting, then structure identification, then safety qualification.

Report0.05%

Identify0.10%

Qualify0.15%

Below 0.05%Not required to be reported individually.

0.05% to 0.10%Reported in batch results; structure not yet required.

Above 0.15%Must be qualified with safety data, or reduced.

Quick check: where does an impurity sit against ICH Q3A?

Enter the maximum daily dose of the drug substance and the level of a single impurity. The checker applies the Q3A(R2) thresholds, including the 1.0 mg/day rule that takes over at higher doses. It is a learning aid for understanding how the thresholds work, not a regulatory decision tool.

Maximum daily dose 0.5 g/day

Impurity level (% w/w) 0.08%

Or type an exact level (%)

Reporting

Identification

Qualification

Q3A applies to new drug substances. Products, excipients and pharmacopoeial monographs can set different or tighter limits.

Residual solvents: what ICH Q3C controls

Solvents are used throughout synthesis, crystallisation and purification, and they are never removed completely. Q3C sorts them into three classes based on toxicity and sets limits as a permitted daily exposure, also expressed as a concentration in ppm. The guideline applies to drug substances, excipients and drug products, so every component counts towards what the patient finally receives.

For buyers, the practical question is which solvents the manufacturer's route uses, and whether the supplier can state them. A material made with a Class 2 solvent needs data showing the residue is below its limit. Recovered or recycled solvents can bring their own contaminants, which also matters for nitrosamine risk.

Class 1 · avoid

Known or strongly suspected human carcinogens and environmental hazards

Not used unless strongly justified, with very low concentration limits.

Benzene2 ppm
Carbon tetrachloride4 ppm
1,2-Dichloroethane5 ppm
1,1-Dichloroethene8 ppm

Class 2 · limit

Solvents limited because of inherent toxicity

Each has its own PDE and concentration limit.

Methanol3,000 ppm
Toluene890 ppm
DMF880 ppm
Dichloromethane600 ppm
Acetonitrile410 ppm

Class 3 · low toxic potential

Solvents generally acceptable at higher levels

Up to 5,000 ppm (0.5%) is generally acceptable without justification.

Ethanol≤ 5,000 ppm
Acetone≤ 5,000 ppm
Ethyl acetate≤ 5,000 ppm
Isopropanol≤ 5,000 ppm

Concentration limits shown as commonly summarised from ICH Q3C; always check the current revision.

Elemental impurities: what ICH Q3D controls

Q3D covers elemental impurities such as lead, cadmium, arsenic and mercury, and metal catalysts such as palladium and nickel. It sets permitted daily exposures and expects a risk assessment covering all sources, including raw materials, equipment and container closures. The tiles show oral PDEs as commonly quoted from Q3D(R2). Parenteral and inhalation limits are lower for most elements.

Class 1CdCadmiumOral PDE 5 µg/day

Class 1PbLeadOral PDE 5 µg/day

Class 1AsArsenicOral PDE 15 µg/day

Class 1HgMercuryOral PDE 30 µg/day

Class 2ACoCobaltOral PDE 50 µg/day

Class 2AVVanadiumOral PDE 100 µg/day

Class 2ANiNickelOral PDE 200 µg/day

Class 2BPdPalladiumOral PDE 100 µg/day

Catalyst residuesPd, Ni, Pt and similar metals used in hydrogenation and coupling steps of API and intermediate synthesis.

Mineral excipientsNaturally sourced fillers and salts can carry Class 1 elements from the ore or mined source.

Equipment and utilitiesStainless steel contact, water and processing aids can contribute metals.

Container closuresPackaging is a recognised source in the Q3D risk assessment, especially for liquids.

Mutagenic impurities: what ICH M7 adds

ICH M7(R2) is the guideline for DNA-reactive (mutagenic) impurities. It classifies impurities by mutagenic and carcinogenic potential. Where no compound-specific data exist, it uses a threshold of toxicological concern of 1.5 µg per day for lifetime exposure. That is far below the percentage-level thresholds of Q3A, which is why a trace mutagenic impurity can matter more than a larger ordinary one.

1Known mutagenic carcinogensControlled at a compound-specific acceptable limit.

2Known mutagens, unknown carcinogenic potentialControlled at or below the TTC-based limit.

3Alerting structure, no mutagenicity dataControl at TTC, or test (for example, Ames) to reclassify.

4Alert shared with the API, which tested negativeTreated as an ordinary impurity.

5No alert, or data show no mutagenicityTreated as an ordinary impurity.

Less-than-lifetime acceptable intakes for an individual impurity

120 µg/dayTreatment up to 1 month

20 µg/dayMore than 1 to 12 months

10 µg/dayMore than 1 to 10 years

1.5 µg/dayMore than 10 years to lifetime

Nitrosamines belong to M7's "cohort of concern", so the TTC does not apply to them. They have compound-specific or category-based acceptable intakes, covered in section 09.

Why do impurity profiles matter so much?

Select a panel to expand it. Each one is a reason why QA and regulatory teams look past the assay figure.

Patient safety

Some impurities are toxic, mutagenic or carcinogenic at very low levels. The diethylene glycol and ethylene glycol contamination cases in syrups showed the cost of missing them.

Reactivity

Impurities such as peroxides, aldehydes, reducing sugars or nitrite in pharmaceutical excipients can react with an API and form degradants or nitrosamines.

Stability and shelf life

Impurities can catalyse degradation in the finished product, cutting shelf life or producing out-of-specification results on stability.

Regulatory filings

The profile is part of the approved specification. A new impurity, or a higher level, can require new data or approval.

Process performance

Impurities in pharmaceutical intermediates can reduce yield or poison catalysts in later steps.

Excipient impurities that react with APIs

Peroxides Oxidation

Found at varying levels in povidone, crospovidone, polyethylene glycols and polysorbates. They can oxidise sensitive APIs.

Aldehydes Adducts

Formaldehyde and related traces, for example from the breakdown of PEGs, can react with amine groups on an API.

Reducing sugars Maillard

Lactose and similar sugars can react with primary and secondary amine APIs, causing discolouration and degradants.

Nitrite Nitrosamines

Trace nitrite in common excipients is a named source of nitrosating agent. It can react with amine APIs to form NDSRIs.

09 · Regulatory update

What changed for nitrosamines in 2026?

Nitrosamines form when amines meet nitrosating agents such as nitrite, typically under acidic conditions. Raw materials can supply either side of that reaction. Since 2018, regulators have required manufacturers to assess nitrosamine risk across APIs and finished products. The rules kept tightening through 2026, especially for nitrosamine drug substance-related impurities (NDSRIs), which form from the API's own structure.

Amine source

Amine-containing solvents such as DMF, DMAc and NMP
Amine reagents and catalysts
The API itself (secondary or tertiary amines)
Recovered solvents

Nitrosating agent

Nitrite in excipients
Nitrite in water or processing aids
Nitrous acid formed under acidic conditions
Contaminated recovered materials

→

Nitrosamine risk

Small-molecule nitrosamines (for example, NDMA)
NDSRIs formed from the API
Must be assessed against acceptable intakes

2018 onwardNitrosamines become a defined riskDetections in some medicines lead to required risk assessments across the industry.

20 Mar 2026EMA guideline finalisedThe revised guideline on the chemistry of active substances is finalised.

24 Jul 2026FDA NDSRI updateThe FDA updates its NDSRI recommendations and adds API-specific entries, as reported in industry analysis.

1 Sep 2026EMA guideline appliesThe revised EMA guideline takes effect. The acceptable intake list (Appendix 1) continues to be updated.

Carcinogenic potency categorisation approach (CPCA)

For an NDSRI without compound-specific data, the CPCA assigns a potency category from its structure, and each category carries an acceptable intake. In the FDA approach for unlisted NDSRIs, 26.5 ng/day is the conservative baseline. Proposing a higher limit based on the CPCA needs prior approval.

Category 126.5ng/day

Category 2100ng/day

Category 3400ng/day

Category 41,500ng/day

Category 51,500ng/day

CPCA category limits as commonly published by regulators; confirm against current FDA and EMA pages for each case. Amine solvents are also covered in our guide to solvents and intermediates in pharma manufacturing.

10 · Change control

A cheaper source can carry a different risk

The same material from a different manufacturer, route or site can contain different impurities, including mutagenic ones, even at the same assay. Relabelled or repacked material can hide the original source. Regulators treat a change of API source, or of a critical starting material, as a change that needs assessment and often prior approval. The user must also re-evaluate the impurity profile.

Know the originAlways know the original manufacturer and site.

Compare profilesCompare impurity profiles before switching.

Use change controlTreat every source change through change control.

Check filingsCheck whether the change needs regulatory notification or approval.

How are impurities actually tested?

Each part of the profile needs its own technique. A COA that lists only assay and identification has not looked at most of these. Knowing the methods helps you judge whether a COA is meaningful.

HPLC / UPLCRelated substances

Separates and quantifies organic impurities and degradation products against specified and unspecified limits.

GC-HSResidual solvents

Headspace gas chromatography detects volatile solvents against Q3C class limits.

ICP-MS / ICP-OESElemental impurities

Measures metals such as Pb, Cd, As, Hg, Ni and Pd at trace levels in line with Q3D.

LC-MS/MS · GC-MS/MSNitrosamines

Highly sensitive methods for trace nitrosamines and NDSRIs at ng/day-relevant levels.

IC / colorimetricNitrite in excipients

Used to measure nitrite, which formulators now request to model nitrosamine risk.

KF · LODWater and volatiles

Karl Fischer and loss on drying, which affect stability and reactive degradation.

Reading a COA: what a useful one shows

A certificate of analysis is only as useful as the tests on it. Compare the two illustrative COAs below. Both report the same assay, but only one gives a QA team enough to assess the impurity profile.

COA · Profile-readyUseful

Assay (on dried basis)	99.5%, method referenced
Identification	IR / HPLC, complies
Specified impurity A	Result with limit and method
Any unspecified impurity	Result vs general limit
Total impurities	Result with limit
Residual solvents (Q3C)	Named solvents with ppm
Elemental impurities (Q3D)	Statement or data
Nitrosamine risk / nitrite	Statement; nitrite data for excipients
Monograph	IP / BP / Ph. Eur. / USP–NF stated
Manufacturer and site	Named

TRACEABLE

COA · Assay-onlyNot enough

Assay	99.5%
Appearance	Complies
Specified impurities	Not reported
Unspecified impurities	Not reported
Residual solvents	Not reported
Elemental impurities	Not addressed
Nitrosamine risk	Not addressed
Monograph	"Pharma grade" (unspecified)
Manufacturer	Not disclosed

GAPS

What should buyers request from suppliers?

Tick off each item as you add it to your supplier request. When you're done, copy the list straight into an email or purchase specification.

Specification and COANamed impurities with limits and methods, not only assay and identification.

Original manufacturerName and site, and how the material was handled if it was repacked.

Risk statementsResidual solvents (Q3C), elemental impurities (Q3D) and nitrosamines, including nitrite levels for excipients where relevant.

Pharmacopoeial and GMP statusThe monograph met (IP, BP, Ph. Eur., USP–NF) and the GMP standard of the manufacturing site.

Change notificationA commitment to notify changes of route, site, starting materials or specification before supply.

Retained samples and own testingIndian rules require testing of each batch of raw material before use.

0/6

Tick the items you will request from your supplier.

What should buyers watch into 2027?

FDA and EMA nitrosamine updates

Further changes to nitrosamine acceptable intakes and NDSRI lists.

Draft ICH Q3E

The draft guideline on extractables and leachables, which extends impurity thinking to packaging and process contact.

Indian Pharmacopoeia and CDSCO

IP updates and CDSCO action on raw material testing and nitrosamines.

Nitrite data on excipients

More formulators asking suppliers for nitrite and nitrosamine data on excipients.

Note: This article is general information as of 3 November 2026, drawn from the sources listed and the ICH guidelines as commonly summarised. It is not regulatory advice. Limits depend on the product, dose, route and market; check the current guidelines, pharmacopoeias and regulator publications for each case.

Talk to Chelora Pharmachem

Documented pharma raw materials, from qualified manufacturers

Chelora Pharmachem supplies pharmaceutical excipients, intermediates and vitamin ingredients, sourced from qualified manufacturers with verified specifications and complete documentation. Share the product, pharmacopoeia, grade, quantity and destination for a quote.

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What are the most asked questions about impurity profiles?

What is an impurity profile?

A description of the identified and unidentified impurities typically present in a batch of a substance, with their levels. It shows not only how pure the material is, but which other substances are present. That is what decides safety and regulatory acceptability.

Why is assay alone not enough?

Two batches can both assay 99.5% and still differ in the remaining 0.5%. If one contains a mutagenic, toxic or reactive impurity, it may be unsafe or unacceptable even though its assay passes. That is why specifications list named impurities, residual solvents and elemental limits, not only purity.

What are the ICH Q3A thresholds for impurities in a drug substance?

For a maximum daily dose up to 2 g, the reporting threshold is 0.05%. The identification threshold is 0.10% or 1.0 mg per day, whichever is lower. The qualification threshold is 0.15% or 1.0 mg per day, whichever is lower. Lower thresholds apply above 2 g a day.

What does ICH Q3C control?

Residual solvents. It sorts solvents into three classes. Class 1 solvents are to be avoided (such as benzene). Class 2 solvents are limited because of toxicity (such as methanol, toluene and DMF). Class 3 solvents have low toxicity and are generally acceptable up to 5,000 ppm without justification.

What does ICH Q3D control?

Elemental impurities, such as lead, cadmium, arsenic and mercury, and metal catalysts such as palladium and nickel. It sets permitted daily exposures and expects a risk assessment covering all sources, including raw materials, equipment and container closures.

What is ICH M7?

The guideline for DNA-reactive (mutagenic) impurities. It classifies impurities by mutagenic and carcinogenic potential. Where no compound-specific data exist, it uses a threshold of toxicological concern of 1.5 µg per day for lifetime exposure.

How do raw materials contribute to nitrosamine risk?

Nitrosamines form when amines meet nitrosating agents such as nitrite. Raw materials can supply either side: nitrite in excipients, amine-containing solvents such as DMF, DMAc and NMP, amine reagents and recovered solvents. Regulators expect manufacturers to assess these sources, and supplier nitrite data is increasingly requested.

What changed for nitrosamines in 2026?

Reported changes include:

an FDA update to its NDSRI recommendations on 24 July 2026, adding API-specific entries;
the EMA's revised guideline on the chemistry of active substances, finalised on 20 March 2026 and effective from 1 September 2026;
continuing updates to the EMA list of acceptable intakes.

Why does a change of source or route matter?

A different route, plant or starting material can produce different impurities even at the same assay. Regulators treat a change of API source, or of a critical starting material, as a change needing assessment and often prior approval, and the user must re-evaluate the impurity profile.

Q10

What should buyers ask suppliers for?

The main items are:

the specification and a COA for each batch, with named impurities and methods;
the original manufacturer's name and site;
residual solvent, elemental impurity and nitrosamine risk statements;
for excipients, nitrite data where relevant;
a commitment to notify changes of route, site or starting materials.

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Supply & Sourcing

The impurities in the last 0.5% are what decide acceptance

What is the difference between purity and an impurity profile?

Assay or purity

Impurity profile

Specified impurity

Unspecified impurity

Residual solvents and elemental impurities

Which ICH guidelines set the limits?

ICH Q3A(R2) and Q3B(R2)

ICH Q3C: residual solvents

ICH Q3D: elemental impurities

ICH M7(R2): DNA-reactive impurities

The Q3A ladder for a drug substance (dose up to 2 g/day)

Quick check: where does an impurity sit against ICH Q3A?

Residual solvents: what ICH Q3C controls

Known or strongly suspected human carcinogens and environmental hazards

Solvents limited because of inherent toxicity

Solvents generally acceptable at higher levels

Elemental impurities: what ICH Q3D controls

Mutagenic impurities: what ICH M7 adds

Less-than-lifetime acceptable intakes for an individual impurity

Why do impurity profiles matter so much?

Patient safety

Reactivity

Stability and shelf life

Regulatory filings

Process performance

Excipient impurities that react with APIs

What changed for nitrosamines in 2026?

Carcinogenic potency categorisation approach (CPCA)

A cheaper source can carry a different risk

How are impurities actually tested?

Reading a COA: what a useful one shows

What should buyers request from suppliers?

What should buyers watch into 2027?

FDA and EMA nitrosamine updates

Draft ICH Q3E

Indian Pharmacopoeia and CDSCO

Nitrite data on excipients

Documented pharma raw materials, from qualified manufacturers

What are the most asked questions about impurity profiles?

What is an impurity profile?

Why is assay alone not enough?

What are the ICH Q3A thresholds for impurities in a drug substance?

What does ICH Q3C control?

What does ICH Q3D control?

What is ICH M7?

How do raw materials contribute to nitrosamine risk?

What changed for nitrosamines in 2026?

Why does a change of source or route matter?

What should buyers ask suppliers for?

Related reading and sources