Potency Basis — As-Is, Dry and Anhydrous Foundations for Assay Calculations

This topic is part of the SG Systems Global regulatory & operations glossary.

Updated November 2025 • Batch-Specific Potency, Potency Adjustment Factor, LOD Adjustment, % Solids Basis • Assay, Basis, GMP, Batching

Potency basis describes the reference condition used to express assay or strength of a material – typically as-is, dry basis or anhydrous basis. The same lot can legitimately have three different “potency” numbers depending on whether moisture, volatiles or water of hydration are mathematically removed from the calculation. In regulated manufacturing, potency basis must be declared and used consistently; otherwise batch-specific potency, potency adjustment factors and dose calculations quickly become misleading or irreconcilable.

“Potency is only meaningful when you know the basis. Without that, 98 % can mean three different things – and none of them match the label claim.”

1) Why Potency Basis Matters

Two numbers can look identical – “98.5 % potency” – yet represent different realities depending on basis. On an as-is basis, 98.5 % potency includes whatever water, solvent or volatiles are present in the material at the time of testing. On a dry basis, the same chemical assay is adjusted to remove the influence of moisture; the percentage describes the composition of the dry residue. On an anhydrous basis, the calculation also strips out water of hydration built into the molecular structure.

For GMP manufacturers, this is not an academic distinction. The potency basis used by the lab must match the basis assumed by the recipe formulation and the execution system. If the batch is dosed using an as-is potency while the specification is defined on a dry basis, operators may add the wrong amount of active substance even though every individual calculation is mathematically correct in isolation. Potency basis is therefore a core piece of master data, not an optional lab detail.

2) As-Is Basis

As-is basis (sometimes called “as-received” basis) expresses potency using the total mass of the sample as the denominator. Moisture, volatiles and solvent present at the time of sampling are all included. If a sample weighs 1.000 g and contains 0.970 g of the active chemical and 0.030 g of water, the as-is potency is 97.0 %.

As-is basis is often attractive because it reflects the material the plant actually handles; scales and feeders see the moist powder or solution, not the dry residue. It is a natural fit for weighing, dosing and inventory control in WMS and MES. However, it can complicate comparison across lots, particularly when moisture content is highly variable. In many regulated settings, the underlying specification is defined on dry or anhydrous basis, with as-is values derived via a controlled LOD adjustment step for use in execution systems.

3) Dry Basis

Dry-basis potency removes the influence of moisture or volatile content from the denominator. Using the earlier example (0.970 g active, 0.030 g water), the dry residue is 0.970 g and the dry-basis potency is 100 % active on a dry basis. In practice, the dry basis may still include other excipients or non-volatile components; the key point is that water and volatiles are excluded.

Dry-basis calculations typically rely on loss-on-drying (LOD) adjustment or moisture results from Karl Fischer titration. The lab determines both chemical assay and moisture; the system then converts as-is assay to dry-basis assay. Specifications for actives, premixes and intermediates are often written on a dry basis because it stabilises comparisons across lots and over time. When a recipe is written assuming 100 % dry-basis potency, all potency-related calculations in MES should be based on the same dry-basis values, not on raw as-is figures.

4) Anhydrous Basis

Anhydrous basis goes one step further and removes both free moisture and bound water of hydration from the calculation. Many APIs and excipients exist as hydrates – the label might describe “X·H₂O” or a monohydrate, dihydrate or other stoichiometric form. On an anhydrous basis, potency is expressed relative to the mass of the pure, water-free chemical entity.

For example, if a monohydrate is 90 % active on an as-is basis, tests may show that, after correcting for surface moisture and water of hydration, the material corresponds to 100 % of the anhydrous active on a molar basis. The pharmacopeial specification may then require assay to be expressed on an anhydrous basis. In that case, recipes, batch-specific potency values and potency adjustment factors must all reference the same anhydrous basis; otherwise the amount of active substance charged per batch will not match the intended label claim.

5) Percent Solids Basis for Liquids and Slurries

For solutions, slurries and suspensions, potency may also be expressed on a percent solids basis. Here, the denominator is the mass of non-volatile solids rather than total mass. Concentrated liquid APIs, enzyme solutions, syrups and some cosmetic intermediates are commonly characterised by % solids and assay on solids basis.

In these systems, potency basis often has two layers:

• % solids describes how much solid material exists per unit of liquid;
• assay on solids basis describes how much active exists per unit of solid.

The effective potency on an as-is basis is then the product of the two. When building concentration-adjusted charges and dynamic recipe scaling, it is essential that MES and ERP understand that the declared potency is contingent on a solids basis, not directly on total volume or mass of the liquid. Otherwise, dose calculations and mass balance will drift as density and solids content vary over time or across lots.

6) Linking Potency Basis to Batch-Specific Potency

Batch-specific potency is the lot-level strength value used by the plant. Potency basis defines how that number should be interpreted. Every potency value in master data should therefore be stored alongside its basis. Typical attributes might include:

• Potency value (e.g. 97.8 );
• Potency basis (as-is, dry, anhydrous or solids);
• Moisture / LOD result used to derive dry-basis values;
• Solids or solvent content where applicable;
• Reference standard and analytical method information via an analytical lot link.

Once this is in place, the system can reliably calculate potency adjustment factors, convert between bases if required and present clear, basis-specific values to operators and QA reviewers inside batch weighing, eBMR and process validation documentation.

7) Impact on Potency Adjustment Factors and Corrected Active Content

The declared potency basis directly affects the potency adjustment factor and the calculation of corrected active content. If the recipe assumes 100 % potency on an anhydrous basis and the laboratory reports potency on an as-is basis, the system must either convert the lab result to an anhydrous basis first or clearly flag the mismatch. Using as-is potency directly would under- or over-dose the batch depending on moisture content.

For example, suppose a material is 95.0 % assay on a dry basis and 4.0 % moisture based on LOD. If the specification is written on a dry basis and the batch is formulated at 100 % dry-basis potency, then the system should calculate the factor using 95.0 %, not the lower as-is value. If the same material is used in a different product where the recipe is written on an as-is basis, the system may need to derive the appropriate as-is potency from the same underlying data, then calculate the factor accordingly. In both cases, documenting the basis used in each calculation step is essential for defending the logic during audit.

8) LOD Adjustment, Moisture Results and Basis Conversions

LOD adjustment is the primary bridge between as-is and dry-basis potency. The lab determines both chemical assay and LOD; the system then calculates:

• Dry-basis assay = As-is assay ÷ (1 – LOD fraction);
• As-is assay = Dry-basis assay × (1 – LOD fraction).

For hydrates and materials specified on an anhydrous basis, additional stoichiometric conversions may be required. Where multiple conversions occur (for example, as-is → dry → anhydrous → solids), it is usually better to capture the final potency directly on the required basis in master data and keep the conversion logic under laboratory control, rather than allowing multiple independent conversions in execution systems.

From a compliance perspective, the key is that all conversions are traceable, reproducible and aligned with pharmacopeial or regulatory expectations. Basis declaration in the test method, test method validation (TMV) and specifications should match the basis used in recipes, QbD design space and PPQ studies.

9) Potency Basis in Test-Driven Setpoint Adjustment

Potency is often one of several tests used in test-driven setpoint adjustment. Solids, pH, viscosity and titer can all impact the amount of material or diluent to be added. In these multi-parameter strategies, potency basis ensures that assay data interacts correctly with other test results.

For example, a concentrate may be controlled by both titer (units/mL) and solids (% w/w on a solids basis). The effective potency used for batching may be a function of both. If the potency basis is not explicitly defined – and aligned with how solids and titer are expressed – the resulting calculations become opaque and difficult to verify. Clear use of potency basis in master data and calculation documentation simplifies validation and makes it easier to explain the rationale behind automated setpoint changes to regulators and technical reviewers.

10) Data Integrity, Audit Trails and Analytical Lot Links

Because potency basis influences dosing and label claim, it is a GxP-relevant attribute. Changes to basis (for example, switching a material from as-is to dry-basis specification) must be visible in audit trails and managed under change control. Basis assumptions embedded in spreadsheets or local calculations are hard to track; embedding basis explicitly in master data and calculation logic is far more robust.

An analytical lot link helps by tying potency (with its basis) back to the underlying lab results and test methods. If basis changes over time, the system can show which lots and batches used each basis, how conversions were performed and what impact that had on potency-normalised yields and stability studies. This level of traceability is often critical during regulatory inspections, especially when investigating OOS or OOT results that may be influenced by differences in how potency was expressed or interpreted over time.

11) Typical Use Cases Across Industries

Potency basis is relevant wherever materials contain water, solvents or bound moisture that influence assay:

• Pharmaceuticals and biologics: hydrates, solvates, lyophilised materials and intermediates with variable moisture content.
• Dietary supplements: botanical extracts, vitamin premixes and probiotics where potency and solids content evolve during processing or storage.
• Food and beverage: enzyme preparations, flavours, colours and fortification premixes measured on a % solids or anhydrous basis.
• Cosmetics and personal care: active ingredients supplied as hydrates or concentrates where label limits refer to the anhydrous active.
• Chemicals and speciality materials: catalysts and functional additives where activity is specified on an anhydrous or solids basis.

In each case, clearly defining and using potency basis keeps formulations, tests and execution logic aligned. It also reduces the risk of subtle, long-running dosing errors that only surface when yields, stability results or field complaints begin to drift in ways that are hard to explain.

12) Common Pitfalls and Basis-Related Errors

When potency basis is not managed explicitly, several predictable failure modes appear:

• Basis mismatch: lab reports potency on a dry basis, while recipes and MES treat the same value as as-is.
• Silent conversions: operators or analysts perform one-off conversions between bases using spreadsheets, leaving no trace in the batch record.
• Mixed bases across materials: some APIs controlled on as-is basis, others on dry basis, without clearly documenting which is which in master data.
• Inconsistent solids definitions: % solids defined differently across suppliers, methods or materials without harmonisation in the specification.
• Unclear label claim linkage: label strength defined on an anhydrous basis, while process calculations quietly use as-is potency, leading to unexplained assay bias.

Addressing these problems usually requires a master-data clean-up, explicit declaration of potency basis for each controlled material, and updates to SOPs, test methods and recipe documentation so that everyone – lab, QA, manufacturing and regulatory – is working from the same assumptions.

13) Practical Implementation Steps

For organisations formalising potency basis, a practical approach may include:

• Reviewing all potency-controlled materials and documenting the intended basis for each.
• Aligning specifications, pharmacopeial references and quality agreements with that basis.
• Updating laboratory methods so that assay and moisture results support the required conversions.
• Exposing basis as an explicit attribute in LIMS, ERP and MES master data, not just as text in methods or CoAs.
• Revalidating calculations for batch-specific potency, potency adjustment factors and potency-normalised yields using the clarified basis.

Once basis is treated as a controlled parameter rather than an implicit assumption, potency-adjusted batching becomes easier to validate, explain and defend, and the likelihood of basis-related deviations or investigations drops significantly.

FAQ

Q1. Is potency basis the same as moisture basis?
No. Moisture basis describes how water content is reported (for example, % w/w). Potency basis describes how the active assay is expressed relative to moisture and other components. Moisture results are often used to convert between as-is and dry-basis potency, but the two concepts are distinct.

Q2. Do all materials need a declared potency basis?
Any material with a controlled potency or assay should have a declared basis, even if it is simply as-is. For simple excipients used by weight only, basis may be less critical, but documenting it still aids clarity and future changes.

Q3. Can we change potency basis after a product is on the market?
Yes, but changes to potency basis can affect dose calculations, specifications and validation data. They should be handled under formal change control, with impact assessment on lab methods, recipes, historical data and regulatory filings.

Q4. How should potency basis appear on certificates of analysis?
CoAs should clearly state both the potency value and the basis (for example, “Assay: 98.5 % on anhydrous basis”). This allows manufacturing systems to interpret results correctly and avoids silent conversions or assumptions at the point of use.

Q5. What is a practical first step to standardise potency basis?
Start by inventorying all potency-controlled materials, noting how assay is currently reported and used. Then agree, material by material, whether the long-term basis should be as-is, dry or anhydrous, and update specifications, test methods and master data to reflect that decision.

Related Reading
• Potency & Batching: Batch-Specific Potency | Potency Adjustment Factor | Potency / Assay Adjustment
• Test-Driven Batching: LOD Adjustment | % Solids Basis | Concentration-Adjusted Charge | Test-Driven Setpoint Adjustment
• Yield, Mass Balance & Records: Mass Balance | Potency-Normalised Yield | Active-Equivalent Consumption | Electronic Batch Record (eBMR)