Impurity Preparation
Separation and preparation of impurities, degradation products and intermediates from mg to kg scale. What is delivered is not just a sample but a set of five — sample, purity, structure, assay and traceable records — ready for impurity profiling, method validation, regulatory filing and deficiency responses.
We undertake the separation and preparation of related substances, degradation impurities and synthetic intermediates, at scales from mg-level reference standards to kg-level intermediates. Preparative chromatography (normal phase / reversed phase, with SFC as an option) is combined with crystallization and extraction to reach purities above 98%, with structural confirmation (NMR / MS) and a COA available. Suited to impurity profiling, in-house reference standards, method validation and regulatory filing.
8–12 weeks for difficult cases
to give a feasibility assessment
to DAC Ø600 mm
DAC with crystallization
01 · Why impurities have to be prepared: the three-tier limits of ICH Q3A
ICH Q3A(R2) divides organic impurities into three bands by level, each with a defined regulatory action. Every unknown peak falling in the 0.10%–0.15% band creates a definite requirement — isolate and identify its structure, or change the process so that the impurity falls below 0.10%; the latter usually costs more.
| Level band | Regulatory action required | Corresponding service |
|---|---|---|
| Below 0.05% (reporting threshold) | Need not be listed in the filing dossier | — |
| 0.05% – 0.10% | The measured value must be reported; a reliable quantitative method must be established | A reference standard is needed for method validation → P1 P5 |
| 0.10% – 0.15% Identification to qualification threshold | A defined structure is required: isolation → enrichment → structure elucidation | Full preparation and confirmation → P1 P2 P3 P4 P5 |
| Above 0.15% (qualification threshold) | Safety qualification is required, or the process must be adjusted to bring it below the limit | — |
Where impurities arise along the process chain
| Point in the process chain | Origin of the impurity | Typical classes |
|---|---|---|
| Starting material | Carried in with the material | Impurities in the starting material itself, homologues, positional isomers;changes whenever the supplier changes |
| Intermediate A / B | Formed in the reaction | Side reactions, over-reaction, incomplete conversion (des- / truncated species); isomerization, racemization, dimerization, incomplete deprotection; derivatives of residual reagent, catalyst or ligand |
| Crude / purified API | Not removed during purification | Components enriched in the mother liquor, co-crystallized impurities, solvent adducts |
| Drug product / shelf life | Degradation and interaction | Hydrolysis, oxidation, photolysis, decarboxylation, cyclization; excipient compatibility products (transesterification, Maillard); leachables from packaging, nitrosamines |
Regulatory clauses and the corresponding service actions
| Regulation / guideline | Corresponding service action |
|---|---|
| ICH Q3A(R2) Impurities in New Drug Substances | Defines which impurities must be prepared; anything >0.10% must be structurally identified → the direct basis for P1 + P4 |
| ICH Q3B(R2) Impurities in New Drug Products | Forced degradation, preparation and confirmation as a set → the basis for service line P2 |
| ICH M7(R2) Mutagenic impurities | Trace quantification needs a high-purity reference standard with an accurate assay → P1 + P5 (safety assessment and QSAR are not undertaken) |
| ICH Q2(R2) Validation of analytical procedures | Without a reference standard, method validation cannot be closed out — specificity, response factor and LOQ all require physical material |
| ICH Q3C(R9) / Q3D(R2) | Constrains solvent choice and residue control in work-up; the residual solvent item on the COA follows from this |
| ICH Q6A Specifications | "Specified impurities" must be controlled individually in the specification → a long-term, repeating requirement for reference standards |
| CTD 3.2.S.3.1 / 3.2.S.3.2 / 3.2.P.5.5 | Whether the report can go straight into the filing dossier — the ultimate test of deliverable quality |
| NMPA Technical Guideline on Impurity Research for Chemical Drugs Chinese Pharmacopoeia general chapters 9101 / 0512 | The direct basis for domestic filings and deficiency responses |
| USP <1086> / EP 5.10 | The corresponding requirements for export DMF / CEP projects, where documentation standards are stricter |
02 · Eight demand scenarios: find the one that matches yours
What the customer actually cares about differs with the trigger — some need the deadline met, some the unit price, some the assay accuracy. Matching the scenario before discussing an approach usually saves a round or two of correspondence.
The reviewer requires an unknown impurity to be identified or a reference standard supplied
Initiated by: regulatory affairs and analytical. Timing comes first and purity need only be fit for purpose, butthe report must be in CTD formatso that it can go straight into the dossier.
Completing the identification of peaks above 0.10%
Initiated by: the CMC lead. Usually several impurities at once, fairly price-sensitive, with a relatively relaxed deadline.
An unknown degradant appears in accelerated or long-term samples
Initiated by: quality research. Small quantities, a complex matrix and a target that is often unstable, making ittechnically demanding, with forced degradation needed to enrich it deliberately.
Specificity / response factor / LOQ
Initiated by: analytical method development.An accurate assay matters more than the quantity delivered, and as little as 5–10 mg may be enough.
Spiking studies and demonstration of purge capability
Initiated by: process chemistry. Gram quantities needed, purity may be relaxed to ≥95%, fairly cost-sensitive.
ICH M7 / nitrosamines / sulfonate esters
Initiated by: QC and regulatory affairs. Trace quantification, with high demands on purity and assay accuracy; isotope-labelled internal standards can be sourced through partners.
Scale-up preparation of a key intermediate (non-GMP)
Initiated by: process or procurement. Priced per kilogram, with negotiable lead time, focused on batch consistency and the transferability of process parameters.
Enantiomers, diastereomers and geometric isomers
Initiated by: CMC. Requires chiral preparation, and the sample readily interconverts during separation and storage.
03 · Six service lines, P1–P6
The branch point is whether the target impurity isobtained by isolationorobtained by synthesis— isolable impurities go to P1 / P2, and where isolation is not viable, to P3; the two routes differ several fold in cost and duration. P4 and P5 are an evidence layer on top of either route, and P6 runs separately against capacity.
Impurity isolation and preparation
The main service line. Isolating the target impurity from crude material, mother liquor, crystallization filtrate, API or drug product; reversed phase / normal phase / SFC with fraction collection.
Degradation product preparation
Degradation products are generated deliberately under acid, base, oxidative, thermal or photolytic conditions and then purified, to support stability studies.
Targeted synthesis of impurities
Where isolation is not viable, the impurity is synthesized to the proposed structure. Astaged contractis used: route design → bench trial → scale-up.
Structural confirmation
HRMS for molecular formula, ¹H / ¹³C NMR for the skeleton, 2D-NMR for connectivity and stereochemistry. Combined as required, without unnecessary duplication.
Assay / value assignment
Direct assay by qNMR against an internal standard, without needing a reference standard of the same structure; the mass balance approach is also available.
Scale-up preparation of intermediates
Isolation and purification of key intermediates at 0.1–10 kg scale, with DAC preparative columns and crystallization.
Three standard packages
Full reference standard package
The usual configuration for a deficiency response. Isolation, structural confirmation and assay in one pass, delivered ready for the dossier and for method validation.
Degradation impurity package
For stability studies. Forced degradation and enrichment → isolation and purification → structural confirmation, with degradation conditions and a proposed pathway; technically the more demanding option.
Large-scale preparation
Priced and scheduled against capacity. It shares equipment with the other two but not method development staff, so it does not slow the response to deficiency-driven projects.
04 · Four scale bands: what "mg to kg" actually means
"mg to kg" spans six orders of magnitude, and stated that broadly it conveys nothing useful. The main variable driving cost structure isthe column format used. The table maps delivered quantity, column diameter, purpose and the key constraint onto one another.
| Band | Delivered quantity | Column format / diameter | Typical use | Target purity and key constraint |
|---|---|---|---|---|
| S identification band | 1 – 20 mg | Analytical column Ø4.6–10 mm with repeated accumulation on a fraction collector | Structural confirmation, identification, assignment of trace peaks (T3 · T4) | ≥95% (enough to elucidate the structure); the sample is precious, soaccurate collection matters more than throughput |
| M reference standard band | 20 – 500 mg | Semi-preparative / preparative column Ø20–30 mm | Impurity reference standards, method validation (T1 · T2, a large share of projects) | ≥98%, with an assigned assay value; this band is thebaseline for routine delivery |
| L process band | 0.5 – 20 g | Preparative column Ø50 mm with crystallization; repeated injection accumulation | Spiking and purge studies, method transfer, catalogue stock (T5) | ≥98%, negotiable down to 95%;solvent and media costs begin to dominate |
| XL supply band | 20 g – 10 kg | DAC dynamic axial compression column Ø100–600 mm with crystallization / extraction / concentration | Intermediate supply, process studies (T7) | To the customer's specification; priced per kilogram and scheduled against capacity; efficiency stability and packing quality determine the cost |
Working the material back before a project starts
Whether it can be done can usually be calculated before the contract is signed. The amount of crude required follows from the target quantity, the impurity level and the recovery:
With the same 5 g of crude, an order of magnitude difference in level leads to opposite conclusions:
| Situation | Crude | Level | Theoretical amount | × 40–60% recovery | Against a 20 mg target |
|---|---|---|---|---|---|
| A | 5 g | 1% | 50 mg | 20 – 30 mg | Feasible |
| B | 5 g | 0.1% | 5 mg | 2 – 3 mg | About sevenfold short |
05 · Choosing the technical route: eight cases and how each is handled
An equipment list proves nothing; the decision criteria do. The order below runs from top to bottom; where several conditions apply at once, follow the one furthest down (the tighter constraint wins).
| Situation | Approach |
|---|---|
| Level ≥0.5% · good UV response · Rs >1.5 | Direct scale-up on reversed-phase prep-HPLC— develop the method on an analytical column and scale linearly by cross-sectional area; low cost, and a large share of projects |
| Level <0.3% · precious sample · poor resolution | Analytical column with repeated accumulation on a fraction collector— a small load per injection but accurate collection, suited to samples that cannot be wasted |
| No UV absorbance · no response even at 200 nm | Mass-directed fraction collection, or a universal detector (ELSD / CAD) |
| Highly polar / very water-soluble · unretained in reversed phase | Aqueous-stable C18 / HILIC / polar-embedded phase; or ion pairing; or enrich by ion exchange first, then polish by reversed phase |
| Chiral · diastereomers · geometric isomers | Chiral prep-HPLC or SFC— SFC separates efficiently, uses less solvent and speeds up work-up |
| Weakly polar / highly lipophilic · strongly retained in reversed phase | Normal-phase preparation (silica) or SFC— work-up is simply evaporation, with no water to remove |
| Unstable in the separation system: acid/base sensitive / interconverting / readily oxidized | Neutral buffer system + low temperature + inert gas; work-up switched to lyophilization or salt formation |
| None of the above viable (<0.05%, co-elution that cannot be resolved, but the structure has been proposed) | Move to P3 targeted synthesisunder a staged contract |
06 · Eight difficult cases: symptom → remedy
Routine projects differ little; the difference shows in the difficult ones. The eight below recur in impurity preparation, each with a workable path.
| Difficulty | Symptom | Remedy |
|---|---|---|
| ① Very low level, <0.1% | The peak is so small that a full day of accumulation gives only a few mg | Work back the crude required → ask for mother liquor or another enriched matrix; accumulate over many injections on a fraction collector; if still insufficient, move to targeted synthesis |
| ② No UV absorbance | The UV trace is a flat line and the target peak cannot be located | Mass-directed collection; a universal ELSD / CAD detector. Derivatization must be shown not to alter the structure, so use it with caution |
| ③ Highly polar, unretained | The target elutes together with the solvent peak | Redevelop on aqueous-stable C18 (100% aqueous); HILIC / polar-embedded phase / ion pairing; or enrich by ion exchange first |
| ④ Co-elutes with the main peak | It appears as a shoulder with Rs <1.0, and any cut brings the main peak with it | Change selectivity (C18 → phenyl → PFP → polar-embedded); change pH to exploit the pKa difference; use two-dimensional preparation if necessary |
| ⑤ Isomer interconversion | The prep fraction is 98% but falls to 70% on standing | Switch to a neutral buffer system; form a salt to lock the configuration; cold lyophilization, protection from light, inert gas; shorten the time chain |
| ⑥ The final product is an oil | It cannot be weighed accurately, measured accurately, shipped or stored | Form a salt; azeotrope off the water; add seed crystals to induce crystallization; where it genuinely cannot be solidified, deliver as a standard solution with an assigned value |
| ⑦ Heavy interference from the formulation matrix | Excipients far outweigh the target and foul the column on injection | Remove excipients by extraction or SPE first; where possible, ask for adrug substance stage samplewhich is easier still |
| ⑧ The degradant changes as it is isolated | It continues to convert as soon as it is isolated | Shorten the work-up time chain and assign the value on the spot; deliver cold; state in the contractthe purity at deliveryand a shorter recommended period of use |
07 · Where the capability comes from: impurity preparation built up from the media layer
The distinguishing feature is not the equipment list butmaking our own media— media of the same lot and the same surface chemistry run across all four column diameters (Ø4.6 mm → Ø20–50 mm → Ø100–200 mm → DAC Ø200–600 mm), so once a method is finalized on an analytical column it scales directly in proportion to cross-sectional area.
No need to redevelop the method
Changing column diameter does not change selectivity, so scale-up shrinks from "redevelop the method" to "recalculate the load once".
kg scale kept in house
With DAC preparative column capability, intermediate scale-up stays on the same service line without subcontracting.
Controllable cost at scale
With media costs internalized, solvent and media consumption on gram-scale and larger projects can be kept within bounds.
Media selection can be worked backwards
When a separation proves difficult, pore size, carbon load, endcapping and pH tolerance can be worked back from the problem, with a custom stationary phase where necessary.
08 · The structural evidence chain and assay assignment
Structural confirmation does not mean running every instrument available. Each technique answers one particular question, and they are combined according to structural complexity, so no one pays for spectra that add nothing.
| Level | Technique | Question it answers |
|---|---|---|
| Essential | HRMS high-resolution mass spectrometry | Molecular formula (elemental composition) and degree of unsaturation |
| Essential | ¹H NMR | Proton environments, proton counts and coupling relationships |
| For complex structures | ¹³C NMR + DEPT | Carbon skeleton, quaternary carbons and carbon type assignment |
| New structures / isomers | 2D-NMR（COSY · HSQC · HMBC · NOESY） | Connectivity and stereochemistry |
| Supporting | IR · UV · elemental analysis · melting point · specific rotation | Functional group evidence; UV is also the basis for determining the response factor |
| Definitive | Single-crystal X-ray | Only where the absolute configuration is in dispute |
qNMR (preferred)
Direct assay against an internal standard, without a reference standard of the same structure; fast and traceable to a primary standard.
Mass balance
100% − related substances − water − residual solvent − sulfated ash; suited to samples that can be fully characterized.
Chromatographic normalization
For purity reference only;Not to be used on its own as a quantitative basis。
09 · Project workflow, decision gates and deliverables
Seven swimlanes × seven stages, with four decision gates (G1–G4). The only purpose of publishing the workflow is to reduce uncertainty in outsourcing — who is doing what at each stage, what is being decided, and what happens if the decision is wrong, can all be seen in advance.
| Gate | Position | What is decided | Consequence of getting it wrong |
|---|---|---|---|
| G1 | S1→S2 feasibility at initiation | Whether there is enough crude (worked back from the material balance), what the level is, how the UV response looks, whether it is stable, and whether a more enriched matrix can be supplied | The most immediate in effect. Too optimistic and the material runs short during execution; too conservative and a viable order is lost |
| G2 | S2→S3 method finalization | Whether resolution and loading linearity hold on the analytical column, and whether selectivity is retained after scale-up | Scaling up without verification → resolution falls, components mix, and roughly half the crude is consumed with nothing to show for it |
| G3 | S4→S5 purity confirmation | Work-upafterwardsthe purity re-measured, not the purity of the prep fraction | Impurities that interconvert commonly fall back at this point — cases of 98% in the prep fraction dropping to 70% after lyophilization have occurred. Miss it and the delivery comes back |
| G4 | S6 report review | Review against the regulatory perspective: can the report go straight into the CTD; is the set of spectra complete; is the assignment table complete | The sample passes but the report cannot be used — a fairly common form of hidden failure |
Deliverables
Standard deliverables (included in the base proposal)
- The target sample (amber vial / foil pouch, labelled with lot number, purity and storage conditions)
- COA: appearance, HPLC purity, storage conditions, recommended shelf life
- HPLC purity chromatogram (with full method parameters)
- RRT correspondence check: evidence that the sample delivered is the peak on your chromatogram
- Statement of traceability of the experimental records
- Brief description of the preparation method (excluding proprietary process detail)
Optional deliverables (to be confirmed and priced separately)
- Structural elucidation report (CTD format, with signal assignment table)
- Assay assignment report (qNMR / mass balance)
- Water content (KF), residual solvent (GC), sulfated ash
- Preliminary stability study (storage stability of the impurity itself)
- Support for customer quality audits and regulatory inspections
- Retention sample custody and a commitment to resupply
Indicative durations
| Project type | Feasibility | Method Development | Preparative | Work-up | Confirmation | Total duration |
|---|---|---|---|---|---|---|
| Routine project | 2–3 d | 3–5 d | 3–5 d | 2–3 d | 5–7 d | 3–4 weeks |
| Moderate difficulty | 3–5 d | 5–10 d | 5–10 d | 3–5 d | 5–7 d | 5–7 weeks |
| Difficult case | 5–7 d | 10–20 d | 10–15 d | 5–10 d | 7–10 d | 8–12 weeks |
| Targeted synthesis P3 | 5 d route design | — | 30–60 d synthesis | 5–10 d | 7–10 d | 10–16 weeks |
| kg-scale intermediate P6 | 3–5 d | 5–10 d | Cycled by batch | By batch | — | Scheduled against capacity |
Four non-technical sources of delay:(1) arrival of the crude sample (easily underestimated); (2) NMR queueing; (3) repeated work-up forcing re-preparation; (4) a change of requirement mid-project. The table gives the duration of the technical work in each stage; the actual delivery date follows the schedule agreed when the proposal is confirmed.
Quality documentation and scope limits
Experimental records are complete, continuous and traceable (original spectra, weighing records, method parameters, lot chain); instrument calibration and interim check records are kept; samples and retention samples are managed to the agreed quantity, conditions and period; reports are checked by two people (technical review plus regulatory review). On confidentiality, projects are coded, structures de-identified, access restricted to named staff and an NDA signed in advance; customer compounds do not enter any public catalogue. We can support customer quality audits and regulatory inspections.
- This is atechnical service for R&D purposesand does not cover commercial manufacture under GMP
- We do not undertake impurity preparation for biological macromolecules (antibodies, nucleic acids); peptides are considered case by case
- We do not provide toxicological safety assessment or QSAR prediction (these can be referred to partners)
- Trace analysis such as elemental impurities and residual solvents is not a core service
- We do not act as regulatory agents or write filing dossiers, only the technical reports within them
- We do not promise that "any impurity can be prepared" — a feasibility assessment comes first, then the proposal
10 · Frequently Asked Questions
I have only 5 g of crude — can you produce 20 mg of the impurity at 98% purity?
What if the impurity has no UV absorbance?
The purity passes when it is prepared but falls after a few days — what can be done?
Can you provide a structural confirmation report that meets CTD requirements?
Does 99% chromatographic purity mean an assay of 99%?
Is this GMP manufacture?
How is confidentiality protected?
Can you work at kilogram scale?
How is it quoted, and how soon can I have a proposal?
11 · Submit Impurity Details
Fields marked * are the minimum set needed to complete the material balance and judge the difficulty. Fill these in and we can usually give a feasibility assessment in our reply rather than coming back with questions first.
Impurity preparation enquiry
A feasibility assessment and price range within 1–2 working days of submission; where information is insufficient we state exactly what is still needed.