One Molecule, Four Markets: Bile-Acid Grades and Their Specs

A cosmetic formulator asks for USP grade because it sounds safer than the alternative. A feed mill buys a 95 per cent material and assumes it can be sold into a capsule. A research group orders a catalogue number and treats the assay figure as a specification. Three different mistakes, one shared cause: the assumption that a grade is a number.

A grade is a specification plus a documentary route plus a regulatory position. The number in the assay column is the least informative part of it.

Four markets, four specifications

Market	Specification basis	Documentation	What decides acceptance
Pharmaceutical	Pharmacopoeial monograph where one exists, otherwise a filed in-house specification	Full batch file, CEP or DMF where applicable, TSE/BSE, residual solvents, elemental impurities	The customer's regulatory file and their qualified person
Feed	Feed additive specification, often an industry standard	Authorisation status, composition, stability in feed, safety data	The authorisation, not the certificate
Cosmetic	In-house specification plus safety assessment	Safety data sheet, toxicological assessment, impurity data	The product safety report
Research	Catalogue specification, often assay and identity only	Certificate with limited tests	The researcher's own acceptance criteria

The columns diverge more than the rows suggest. Two materials that both read 99 per cent on a certificate can sit in different rows, because the tests behind the number are different.

What the pharmacopoeial route actually adds

Where a monograph exists, it defines the test panel: identity by infrared and by a chemical reaction, related substances by a specified chromatographic method, assay by titration or by HPLC, loss on drying, residue on ignition, heavy metals, and specific optical rotation for the chiral members of the family.

Three of those tests are the ones that separate a pharmaceutical specification from an industrial one, and none of them appears in an assay figure.

Related substances. A limit on total impurities plus limits on named ones. The named ones are the process-related and degradation-related structures that the compendium has decided matter, and a supplier's in-house method may not resolve them at all.

Specific optical rotation. For a bile acid, this is a check on the stereochemistry of the whole molecule, not only on the chiral centres the assay can see. A material can be 99 per cent pure by area and still carry the wrong epimer at a level that rotation catches and chromatography does not.

Residue on ignition. A crude check on inorganic content that a purely chromatographic specification often omits, and which a customer's elemental impurity risk assessment will expect to see addressed.

None of these is exotic. All of them are absent from a typical industrial certificate.

The industry standard route, and what it is good for

For a synthetically produced bile acid sold into non-pharmaceutical applications, an industry standard provides a common reference: defined test items, defined methods, defined limits, agreed by a technical committee rather than a pharmacopoeial authority. It gives a buyer something to compare quotations against, which is genuinely useful.

It is not a monograph. It does not carry the legal force of a pharmacopoeia, and a certificate that cites it cannot be filed where a compendial monograph is required. The distinction is not a technicality; it is the difference between a document that supports a regulatory submission and one that supports a purchase order.

The expensive mistake, in both directions

Industrial into pharmaceutical. The material may be chemically adequate and the documentation is not. The impurity panel is short, the residual solvent statement may not exist, the microbial limits may never have been tested, and the TSE/BSE position may be a sentence rather than a statement. The customer discovers this at their own filing, which is the worst possible time.

Pharmaceutical into an application that does not need it. The material is over-specified and the price carries tests that add nothing to the application. A feed formulator paying for a chiral purity test they never use is a margin leak that nobody notices because the specification looks impressive.

Both errors come from treating grade as a quality hierarchy rather than a fit between specification and use.

Feed is the market most often misunderstood

Feed additives are regulated as a category of their own. In the EU, placing one on the market requires an authorisation specific to the substance, the target species and the conditions of use, following a safety assessment. A supplier's certificate addresses composition. It does not address authorisation, and it cannot, because the authorisation belongs to the applicant and the use.

A feed customer therefore needs two things from a supplier: a specification that matches the authorised use, and a documentary trail that supports their own dossier. A certificate with an assay figure and nothing else is not enough, however good the number is.

Cosmetics and research are the inverse case

Neither requires a pharmacopoeial grade, and both are sometimes sold one. A cosmetic ingredient needs a safety assessment and an impurity profile, not a monograph. A research reagent needs an identity and an assay, not a batch file.

The risk in these markets is not under-specification in the regulatory sense. It is that the buyer cannot tell what was tested, because the certificate format does not distinguish between "tested and passed" and "not tested". A line that reads "heavy metals: complies" without a method or a limit is a sentence, not a result.

How to choose

Start from the use, then the regulatory route, then the specification, then the supplier. In that order.

1. What is the material going into, and which authority regulates that product?
2. Does a pharmacopoeial monograph exist for this substance, and is it legally applicable in the destination market?
3. If not, what specification will the customer's own file accept?
4. Which tests in that specification are the ones the process actually needs to control?
5. Can the supplier provide the documentation route, not only the certificate?

Most grade confusion disappears at step two, and the rest disappears at step five.

Where this leaves a supply-chain partner

We ask what the material is for before quoting it, because the answer changes the specification, the documents and often the product. Where a customer needs a pharmaceutical route and the substance has no applicable monograph, we say so and describe what an in-house specification would have to contain, rather than selling the nearest catalogue grade and letting the customer discover the gap later.

A grade is a claim about what was tested. The useful question is always the same: which tests, against which limits, and who is entitled to rely on them.

Where the grade question actually starts

It starts with the destination of the material, not with the material. The same drum can be a pharmaceutical starting material, a feed additive, a cosmetic ingredient or a laboratory reagent, and the specification that matters is the one the destination requires rather than the most demanding one available.

Four questions, asked in order, settle it. What is the material going into? Which authority regulates that product in the destination market? Does a pharmacopoeial monograph exist for this substance, and is it legally applicable there? If not, what specification will the customer's own file accept?

Most grade confusion disappears at the third question. A substance with a monograph in one jurisdiction and none in another sits in two different positions, and a supplier who quotes a single grade across both is describing their catalogue rather than the customer's requirement. The ICH Q6A framework is the reference most customers use when no monograph applies, because it describes how a specification is justified rather than what its limits should be.

The documentation asymmetry

The three non-pharmaceutical markets differ from the pharmaceutical one less in their limits than in what they require to be written down.

A feed customer needs an authorisation position, which is a regulatory fact about the substance and the species, and a specification that matches the authorised use. The EFSA assessments and the European Commission feed pages are where that position is established, and a certificate of analysis does not speak to it at all.

A cosmetic customer needs a safety assessment, which is about exposure and toxicology rather than about assay. The specification still matters, and the impurity profile matters more than the assay figure, because the assessment is built on what else is in the material.

A research customer needs an identity and a purity figure, and usually nothing else. That is a real market with real requirements, and it is also where the word grade does the most damage, because a catalogue number looks like a specification and is not one.

The asymmetry has a commercial consequence. A supplier who sends a pharmaceutical-style certificate to a feed customer invites a documentation request the customer does not need. One who sends a research-grade certificate to a pharmaceutical customer invites a qualification failure. Matching the document to the destination is the whole job, and it is the same discipline that sits behind EP grade claims, origin and vegetal claims and the specification work for substances with no monograph.

Frequently asked questions

Is a 95 per cent assay product a lower grade of the same material?

Not necessarily. It is a product released against a different specification, and the assay figure is only one line of it. The more important differences are usually in the impurity profile, the microbial limits and the documentation. A 95 per cent material can be entirely suitable for a feed application and entirely unsuitable for a pharmaceutical one, without either statement being a criticism of the material.

Can we use an industrial-grade bile acid in a pharmaceutical process?

Only after qualifying it against the pharmaceutical specification, which usually means re-purifying it. An industrial standard does not carry the impurity control, the residual solvent control or the microbial control that a pharmaceutical file requires, and the certificate will not tell you what it did not test. Using it directly moves an unquantified risk into a regulated process.

What is the difference between a pharmacopoeia and an industry standard?

A pharmacopoeia is a legally recognised compendium with monographs that carry legal force in the jurisdictions that adopt it. An industry standard, such as a chemical-industry standard for a synthetically produced bile acid, is a voluntary technical consensus used in commerce, not a compendium monograph. Both can be rigorous. Only one is a pharmacopoeia, and they are not interchangeable in a regulatory filing.

Does a feed additive need an authorisation in the EU?

Yes. Feed additives placed on the EU market require authorisation under the feed additives regulation, following an EFSA assessment, and the authorisation is specific to the substance, the species and the conditions of use. A supplier's certificate of analysis says nothing about whether that authorisation exists, and the customer is the party who needs it.

Do cosmetics need a pharmacopoeial grade?

No. Cosmetic products are governed by a safety assessment and a product information file, not by a compendium monograph. The material still needs a specification, a safety data sheet and a toxicological assessment, and the impurity profile still matters, but the route is different and the word grade means something else.

What changes if the material is for laboratory research?

Usually very little documentation and a great deal of reliance on the assay figure. That is a legitimate market, and it is also where grade confusion starts, because a research catalogue number looks like a specification and is not one. A researcher who needs traceability should ask for the batch record extracts that a research-grade product does not normally carry.