Elemental Impurities (ICH Q3D) in Pharmaceutical Intermediates: A Buyer's Guide

What Are Elemental Impurities and Why ICH Q3D Replaced the Old Heavy Metals Test

Elemental impurities are metallic and metalloid trace contaminants — lead, arsenic, cadmium, mercury, palladium, nickel, and others — that can enter pharmaceutical products through catalysts, raw materials, manufacturing equipment, or container closure systems. Unlike organic impurities, these inorganic elements have no therapeutic benefit and can cause neurotoxicity, nephrotoxicity, carcinogenicity, or sensitization even at trace levels.

For decades, the pharmaceutical industry relied on the outdated USP <231> Heavy Metals test, a non-specific colorimetric method using sulfide precipitation. This test measured total “heavy metals” as a group — it could not identify individual elements, lacked sensitivity, and frequently underestimated toxic elements present in pharmaceutical ingredients. The method had been in use for nearly 100 years when it was finally retired.

ICH Q3D, first adopted at Step 4 in December 2014 and revised to Q3D(R2) in April 2022, replaced this approach with a science-based framework that defines element-specific permitted daily exposure (PDE) limits for 24 elements, differentiated by route of administration. The guideline was implemented for new drug products in June 2016 and for previously authorized products in December 2017 across ICH regions.

For pharmaceutical intermediate buyers, the shift from USP <231> to ICH Q3D has a practical consequence: a COA stating “Heavy Metals ≤ 10 ppm” is no longer sufficient evidence of elemental impurity control. Buyers must now look for element-specific data — which elements were tested, by what method, and at what levels relative to established PDEs.

The Four Element Classes: What Intermediate Buyers Must Evaluate

ICH Q3D classifies 24 elements into four classes based on toxicity and the likelihood of occurrence in pharmaceutical manufacturing. This classification determines whether a risk assessment must include a given element.

Class 1: Highest Toxicity — Always Evaluate

Class 1 elements (As, Cd, Hg, Pb) are human toxicants with no permitted use in pharmaceutical manufacturing. Because they are ubiquitous environmental contaminants, ICH Q3D requires their evaluation in all risk assessments, regardless of route of administration or whether they are intentionally used.

Source: ICH Q3D(R2), Appendix 2, Table A.2.1 — PDE values adopted April 2022.

Class 2A: High Probability of Occurrence — Always Evaluate

Class 2A elements (Co, Ni, V) are toxicants with a relatively high probability of appearing in pharmaceutical manufacturing. They must be evaluated in risk assessments for all routes of administration. The most relevant for intermediate buyers is nickel, which is a common component of stainless-steel equipment and Raney nickel catalysts.

Source: ICH Q3D(R2), Appendix 2. Q3D(R2) corrected the Ni PDE from the original Q3D(R1) version.

Class 2B: Low Probability — Evaluate Only if Intentionally Added

Class 2B elements include the platinum-group metals — palladium (Pd), platinum (Pt), iridium (Ir), osmium (Os), rhodium (Rh), ruthenium (Ru) — along with gold (Au), silver (Ag), selenium (Se), and thallium (Tl). These elements are rare in nature and unlikely to appear in pharmaceuticals unless they are intentionally added as catalysts or reagents during synthesis.

For pharmaceutical intermediate buyers, this is the most critical class. If an intermediate’s synthetic route uses a palladium catalyst (e.g., for Suzuki coupling, Buchwald-Hartwig amination, or Heck reaction), the Pd must be included in the risk assessment and controlled. If no Class 2B elements are used in the synthesis, they can be excluded from evaluation with documented justification.

Source: ICH Q3D(R2), Appendix 2. Q3D(R2) corrected the PDEs for gold and silver from the R1 version.

Class 3: Low Oral Toxicity — Route-Dependent Evaluation

Class 3 elements (Li, Sb, Ba, Mo, Cu, Sn, Cr) have relatively low toxicity by the oral route and generally do not require evaluation for oral products unless intentionally added. However, for parenteral and inhalation products, these elements must be considered because their toxicity increases significantly via these routes.

For intermediate buyers, Class 3 matters when the intermediate is destined for an injectable or inhalation product. In that case, elements like chromium (from stainless-steel equipment) and copper (from reaction vessels) become relevant.

Where Elemental Impurities Come From in Intermediate Manufacturing

ICH Q3D Section 5.2 identifies five primary sources of elemental impurities. For pharmaceutical intermediate manufacturing, not all sources carry equal weight:

For most pharmaceutical intermediates, the dominant source of elemental impurities is catalyst residue. A single Suzuki coupling step using 0.5–5 mol% Pd catalyst can introduce 50–500 ppm of palladium into the crude product.

Traditional purification methods (activated carbon treatment, aqueous wash) may reduce this to 10–50 ppm — still above the ICH Q3D oral concentration limit of 10 ppm (based on a 10 g/day dose and the oral Pd PDE of 100 µg/day).

This gap between typical post-reaction levels and the regulatory limit is why catalyst residue control is the central challenge in intermediate elemental impurity management.

The 30% Control Threshold: When Does Your Supplier Need to Test?

One of the most important concepts in ICH Q3D is the control threshold, defined as 30% of the PDE for a given element in the drug product. This threshold determines whether additional control measures — including routine batch testing — are required.

The logic is as follows:

Source: ICH Q3D(R2), Section 5.5 and 5.6; Taiwan CDE FAQ on metal catalyst residue exemption.

What the 30% Threshold Means for Intermediate Suppliers

For intermediate manufacturers, demonstrating that elemental impurity levels are consistently below 30% of PDE allows them to skip routine batch testing for those elements. To justify this exemption, ICH Q3D and regional regulators require supporting data:

• China NMPA CDE guidance (2025):At least 3 consecutive commercial-scale batches or 6 consecutive pilot-scale batches, analyzed by a validated ICP-MS or ICP-OES method, showing elemental impurity levels below 30% of the applicable PDE.
• Taiwan CDE:Accepts any one of three approaches — (1) establish acceptance criteria at an appropriate intermediate, (2) conduct a purge study demonstrating effective catalyst removal, or (3) provide 3 consecutive commercial batches or 6 pilot batches with results below 30% of PDE.
• ICH Q3D lifecycle management:Even when routine testing is skipped, the risk assessment must be reviewed when any manufacturing change occurs — new supplier, process modification, equipment change, or synthetic route alteration.

Source: CDE common Q&A on elemental impurity assessment (August 2025); Taiwan CDE FAQ No. 1245 on metal catalyst residue exemption.

For intermediate buyers, the 30% threshold has a practical implication: a supplier who claims “no routine testing required” for a catalyst element should be able to produce the supporting batch data and risk assessment. If they cannot, the claim is unsubstantiated. For more on evaluating supplier documentation, see our guide on how to read a COA for pharmaceutical intermediates.

Pd, Pt, Ni: Your Intermediate’s Most Likely Elemental Impurities

Three elements dominate elemental impurity concerns in pharmaceutical intermediates: palladium, platinum, and nickel. Understanding why — and what levels to expect — helps buyers evaluate supplier capability.

Palladium (Pd) — Class 2B, Oral PDE: 100 µg/day

Palladium is the most common catalyst metal in modern pharmaceutical synthesis. Suzuki-Miyaura cross-coupling, Buchwald-Hartwig amination, Heck reaction, Sonogashira coupling, and hydrogenation (Pd/C) all use palladium catalysts. These reactions form carbon-carbon and carbon-nitrogen bonds that are central to building complex intermediate structures.

The challenge with Pd is the gap between catalyst loading and the regulatory limit:

Source: ICH Q3D(R2), Section 7 (concentration limit calculation); industry practice per published process chemistry literature.

This table shows why Pd residue control is not trivial: traditional purification brings the level to 10–50 ppm, but compliance requires ≤ 10 ppm (oral) or ≤ 1 ppm (parenteral). Suppliers who specialize in Pd-catalyzed intermediates must employ advanced purification — metal scavengers (e.g., SiliaMetS thiol), recrystallization, or activated carbon with optimized contact time — to close this gap.

Platinum (Pt) — Class 2B, Oral PDE: 100 µg/day

Platinum catalysts (PtO₂, Adams’ catalyst) are used in hydrogenation reactions, particularly for aromatic ring reduction or selective reduction of functional groups. Pt shares the same PDE as Pd (100 µg/day oral, 10 µg/day parenteral) but appears less frequently in modern intermediate synthesis because Pd catalysts are generally more versatile and cost-effective.

Nickel (Ni) — Class 2A, Oral PDE: 200 µg/day

Nickel enters intermediate manufacturing through two pathways: (1) Raney nickel catalysts used for hydrogenation and reductive amination, and (2) stainless-steel equipment (316L contains 10–14% Ni). While the oral PDE for Ni (200 µg/day) is more permissive than Pd, the parenteral PDE (20 µg/day) is 10× stricter, making Ni a significant concern for intermediates destined for injectable products.

Because Ni is a Class 2A element, it must always be included in risk assessments — even when not intentionally added as a catalyst — due to its ubiquitous presence in manufacturing equipment.

ICP-MS vs ICP-OES: Which Method Does Your COA Need?

ICH Q3D does not mandate a specific analytical method, but USP <233> and the harmonized pharmacopeial chapters recommend two techniques: ICP-MS and ICP-OES. Understanding the difference helps buyers evaluate whether a supplier’s COA data is adequate.

Source: QbD Group, “ICP-MS vs ICP-OES analysis: choosing the right elemental impurity testing method” (2025).

What This Means for Your COA

If your intermediate uses a Pd catalyst and the supplier provides only ICP-OES data, the detection limit may be insufficient to demonstrate compliance with the 30% control threshold — especially for parenteral-destined intermediates where the Pd concentration limit is 1 ppm. ICP-MS, with its ppt-level sensitivity, is the appropriate method for catalyst residue analysis at trace levels.

Conversely, for Class 3 elements like copper or tin present at moderate levels, ICP-OES is adequate and more cost-effective. A well-documented COA should specify which method was used for each element and why.

5 Red Flags on a Supplier’s Elemental Impurity Documentation

Red Flag 1: “Heavy Metals ≤ 10 ppm” on the COA.

This phrase indicates the supplier is still using the retired USP <231> sulfide precipitation method, which was replaced by ICH Q3D in 2016–2018. This test cannot identify individual elements and lacks the sensitivity to detect toxic metals at PDE-relevant levels. A Q3D-compliant COA should list specific elements (e.g., “Pd: not detected, LOQ 0.5 ppm, Method: ICP-MS”).

Red Flag 2: Pd catalyst used in synthesis, but no Pd listed on the COA.

If the synthetic route involves a palladium-catalyzed coupling step, Pd must appear in the risk assessment and on the COA — either as a tested result or as a justified exclusion based on supporting data. Its absence suggests the supplier has not conducted a Q3D risk assessment at all. This is especially critical for intermediates like empagliflozin intermediates, where multi-step synthesis often includes metal-catalyzed reactions.

Red Flag 3: Only Class 1 elements tested; no Class 2A or 2B data.

Some suppliers test only As, Cd, Hg, and Pb (the Class 1 “big four”) and assume compliance for everything else. But if the synthesis uses Ni, Pd, or Pt catalysts — or if stainless-steel equipment is involved — Class 2A/2B elements must be evaluated. A risk assessment that ignores catalyst residues is incomplete and will not survive regulatory scrutiny.

Red Flag 4: ICP-OES used for elements requiring ICP-MS sensitivity.

When a catalyst residue must be controlled to sub-ppm levels (e.g., Pd for parenteral products, where the concentration limit is 1 ppm), ICP-OES may not have the detection capability to demonstrate compliance with the 30% control threshold. The COA should use the method appropriate to the required detection limit — ICP-MS for trace-level catalyst residues, ICP-OES for higher-concentration elements.

Red Flag 5: A generic “statement of compliance” without batch-specific data.

Some suppliers provide a letter stating “This material complies with ICH Q3D” without any analytical data. While risk assessment-based exclusion is permitted under Q3D, the supplier should be able to produce the supporting batch data (3 commercial or 6 pilot batches below 30% PDE) and method validation report upon request. A statement alone, without traceable data, is not sufficient evidence of control.

3 Questions to Ask Your Intermediate Supplier About Elemental Impurities

Question 1: “Which elements did your Q3D risk assessment identify as requiring control?”

A competent supplier should be able to list the specific elements — not just “all Q3D elements” — and explain why each was included or excluded. For example: “Pd is controlled because our Step 3 uses a Suzuki coupling with Pd(PPh₃)₄; Ni is evaluated because 316L reactor contact; As, Cd, Hg, Pb are evaluated as Class 1 contaminants.”

Question 2: “At which synthetic step do you control catalyst residues, and what is your acceptance criterion?”

Catalyst residue can be controlled at the step where it is introduced (upstream control), at a later intermediate step, or at the final intermediate. The supplier should specify the control point, the acceptance criterion (ideally below 30% of PDE), and the analytical method used. For intermediates with multiple chiral centers or complex stereochemistry, also review our chiral purity and ee% guide to understand how catalyst steps interact with stereochemical control.

Question 3: “Can you provide the method validation report for your ICP-MS method?”

Method validation is required under ICH Q3D Section 9 and USP <233>. Key validation parameters include: specificity (no matrix interference), accuracy (70–150% recovery), precision (RSD ≤ 20%), and limit of quantitation (at or below the specification limit). A supplier who cannot produce validation data is using an unvalidated method, and the results should not be trusted.

Lifecycle Considerations: When to Re-evaluate Elemental Impurity Risks

ICH Q3D Section 10 requires that elemental impurity risk assessments be maintained throughout the product lifecycle. Any of the following changes should trigger a re-evaluation:

USP <233> Elemental Impurities — Procedures was published as a harmonized standard on April 25, 2025, with an official date of May 1, 2026. The harmonized chapter aligns USP with the European Pharmacopoeia, Japanese Pharmacopoeia, and Indian Pharmacopoeia, incorporating ICH Q3D concepts directly. Suppliers should be aware of this update and ensure their analytical methods meet the revised validation requirements.

Source: USP General Chapter <233> Elemental Impurities — Procedures, harmonized standard, official May 1, 2026.

Additionally, China’s 2025 Pharmacopoeia (effective October 1, 2025) introduces a new chapter on elemental impurities (Chapter 0862) aligned with ICH Q3D, establishing a from-raw-material-to-finished-product elemental impurity control framework. Chinese intermediate suppliers will face increasing scrutiny on elemental impurity data under this updated pharmacopeia.

For buyers managing intermediate storage conditions alongside quality parameters, it is worth noting that storage conditions (temperature, humidity) can also affect elemental impurity levels over time — particularly if packaging materials interact with the product. Q3D risk assessments should account for shelf-life stability, not just initial release testing.

Key Takeaways

1. ICH Q3D replaced the old “heavy metals” testwith element-specific PDE limits for 24 elements across four classes. A COA showing “Heavy Metals ≤ 10 ppm” is outdated and non-compliant.
2. Catalyst residue is the #1 elemental impurity concern for intermediates.Palladium (Pd, Class 2B) is the most common, with typical post-reaction levels of 10–50 ppm vs. a regulatory limit of 10 ppm (oral) or 1 ppm (parenteral).
3. The 30% control threshold determines testing requirements.If elemental impurity levels are consistently below 30% of PDE (demonstrated by 3 commercial or 6 pilot batches), routine batch testing may be skipped. But the supporting data must exist.
4. ICP-MS is the gold standard for trace-level catalyst residue analysis(ppt sensitivity). ICP-OES is adequate for higher-concentration elements but may lack sensitivity for sub-ppm Pd/Pt control.
5. A Q3D-compliant COA should list:specific elements tested, analytical method used (ICP-MS or ICP-OES), batch-specific results, LOQ, and reference to the risk assessment. A generic “complies with ICH Q3D” statement without data is insufficient.
6. USP <233> harmonized standard becomes official May 1, 2026, aligning US, European, Japanese, and Indian pharmacopeias. China’s 2025 Pharmacopoeia also introduces an aligned chapter (0862). Global harmonization is now essentially complete.

References

1. Guideline for Elemental Impurities Q3D(R2). Adopted April 26, 2022. Available at: https://database.ich.org/sites/default/files/Q3D-R2_Guideline_Step4_2022_0308.pdf
2. S. FDA. Q3D(R2) Elemental Impurities — Guidance for Industry. September 2022. Available at: https://www.fda.gov/media/148474/download
3. <233> Elemental Impurities — Procedures, Harmonized Standard. Posted April 25, 2025; Official May 1, 2026. Available at: https://www.usp.org/harmonization-standards/pdg/general-chapters/elemental-impurities
4. QbD Group (Quercus). “ICP-MS vs ICP-OES analysis: choosing the right elemental impurity testing method.” April 2025, updated March 2026. Available at: https://qbdgroup.com/en/blog/elemental-impurity-testing-icp-ms-vs-icp-oes
5. “Elemental impurities per USP and ICH Q3D guidelines.” July 2024. Available at: https://www.labcorp.com/education-events/articles/elemental-impurities-usp-and-ich-q3d-guidelines
6. NMPA CDE. Common Q&A: Assessment and Control of Elemental Impurities in Chemical APIs per ICH Q3D and 2025 Chinese Pharmacopoeia. August 2025.
7. Taiwan CDE. FAQ No. 1245: Exemption of Routine Testing for Metal Catalyst Residues in API Manufacturing. Available at: https://www.cde.org.tw/faq/faq_more?id=1245
8. China Pharmacopoeia 2025 Edition. Chapter 0862: Elemental Impurities(aligned with ICH Q3D). Effective October 1, 2025.