What Is Assay?
Assay measures the amount of active substance in the product. HPLC is the most common method; titrimetric or spectrophotometric methods may also be used per the monograph. The result is expressed as a percentage of the declared content.
Purpose of Assay
The purpose is to verify the product contains the declared dose. Dose deviation creates a direct risk to both efficacy and safety.
Which Products Is Assay Applied To?
- Tablets, capsules and dragées
- Syrups, suspensions and drops
- Injectable solutions
- Creams, gels and ointments
- Active pharmaceutical ingredients
In Which Sectors Is Assay Used?
Standards Related to Assay
- Ph. Eur. 2.2.29 (liquid chromatography)
- Ph. Eur. 2.2.46 (chromatographic separation techniques)
- USP <621> (chromatography)
- ICH Q2(R2) (validation of analytical procedures)
- Relevant product monographs
Assay Conditions
- System suitability
- The system suitability criteria in the monograph must be met in every run
- Reference standard
- Pharmacopoeia or a qualified working standard
- Sample preparation
- Extraction and dilution defined in the monograph
Equipment for Assay
- HPLC / UPLC (with DAD or UV detector)
- Automatic titrator
- UV/Vis spectrophotometer
- Analytical balance (0.00001 g)
- Ultrasonic bath and centrifuge
Sample Requirements for Assay
- The number of units specified in the monograph (tablet, capsule, etc.)
- Batch number and declared dose must be provided
- The specimen must be sent in its original packaging
- Reference standard information must be provided
Duration of Assay
Chromatographic assay, together with sample preparation and the system suitability run, takes several working days.
Assay Procedure
- 1The method and conditions in the monograph are set up.
- 2The reference standard solution is prepared.
- 3A system suitability run is performed and the criteria are verified.
- 4The specimen is prepared per the monograph.
- 5Chromatographic or titrimetric measurement is performed.
- 6Active substance content is calculated as a percentage of the declared value.
Assay Acceptance Criteria
The acceptance criterion is not given on this page: for every active substance and every product, the limit comes from the relevant pharmacopoeia monograph or the approved specification in the marketing authorisation dossier. The pharmacopoeia's general chapter defines the method; the monograph sets the limit.
Evaluation of Results
A result obtained without meeting the system suitability criteria is not valid; these criteria prove the method worked correctly that day. The assay result alone is also not sufficient: content uniformity and dissolution testing show that every unit of the product delivers the correct dose.
Assay Report
- Specimen identification, batch and declared dose
- Monograph and method conditions applied
- System suitability results
- Assay result (% of declared)
- Chromatograms and calculations
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- 2001/83/EC Directive on Medicinal Products for Human Use
- GMP Guide (EudraLex Volume 4)
Pharmaceutical Analysis — What Does This Testing Field Cover?
The section below describes the field that the Assay test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Pharmaceutical analysis determines the identity, purity, quantity and behaviour of an active substance and of the finished product. What sets this family apart is that the methods are largely defined in PHARMACOPOEIAS: the European Pharmacopoeia (Ph. Eur.) and the United States Pharmacopeia (USP) give both the method and the acceptance framework together.
The binding nature of the pharmacopoeial method shapes how the field works. In other sectors a laboratory can choose a suitable method, whereas here the method in the monograph governs; if an alternative method is to be used, its equivalence must be demonstrated. This is what makes results comparable worldwide.
Analyses are carried out in several groups. Identity and assay (HPLC, UV, titration) show what the product is and how much active substance it contains. The impurity profile and residual solvents look for unwanted compounds arising from the manufacturing process. Elemental impurities address metals originating from catalysts and equipment. Dissolution and disintegration behaviour is the most important in vitro indicator of how the drug will be released in the body.
The DISSOLUTION TEST is one of the most critical measurements in the field. It is not enough for a tablet to contain the right amount of active substance; that substance must dissolve at a suitable rate. The dissolution profile is used to assess the effect of formulation changes on bioavailability and holds a central place in generic drug licensing.
METHOD VALIDATION is a mandatory step in this family. If a pharmacopoeial method is used, it is verified that the method works properly under that laboratory's conditions. If an in-house method has been developed, it is validated against parameters such as linearity, precision, accuracy, specificity, limits of detection and quantification, and robustness. A result produced with an unvalidated method cannot be used in a licence dossier.
Stability studies determine shelf life and are the longest-running work in the field. The product is held under defined temperature and humidity conditions, analysed at set intervals, and the results become the basis of the shelf life and storage condition claims. Accelerated conditions give preliminary information but real-time data is what counts.
The microbiological side is a separate body of work: microbial enumeration, testing for specified microorganisms, sterility testing for sterile products and the bacterial endotoxin test. For sterile products, packaging integrity and sterilisation validation also come into play.
Data integrity has moved to the centre of inspections in recent years. It is not enough for the result to be correct; the raw data must be traceable, unalterable and auditable. Validation of electronic record systems has therefore become an inseparable part of analysis.
Method groups in this field
Identity and assay
HPLC, UPLC, UV-Vis spectrophotometry, titration, identity confirmation by FTIR.
Impurities and residues
Related impurities, degradation products, residual solvents (GC headspace), nitrosamine screening.
Elemental impurities
Determination of elemental impurities by ICP-MS and ICP-OES and the associated risk assessment.
Physicochemical
Dissolution and disintegration, hardness, friability, uniformity of dosage units, water content (Karl Fischer), particle size.
Microbiological
Microbial enumeration, specified microorganisms, sterility, bacterial endotoxin, preservative efficacy.
Stability
Real-time and accelerated stability studies; photostability and in-use stability.
Commonly confused in this field
- The pharmacopoeial method is binding; an alternative method may be used only by demonstrating its equivalence.
- A result produced without method validation cannot be used in a licence dossier.
- Accelerated stability does not replace real-time data; shelf life is supported by real-time results.
- The dissolution profile is sensitive to apparatus type, agitation rate and medium; the conditions must be complete in the report.
- A shortcoming in data integrity produces a non-conformity in an inspection even when the result is correct.
- A change of formulation or supplier requires analytical comparison and, where necessary, a new stability study.
Which decisions these results support
- The licence dossier and batch release
- Determining shelf life and storage conditions
- Method transfer and method validation
- Incoming raw material acceptance control from suppliers
- Assessing the effect of a formulation change on bioequivalence
Related Tests
Frequently Asked Questions About Assay
The assay result passed — is the product compliant?
Not on its own. Assay gives the average content; content uniformity is separately needed for unit-to-unit distribution, and dissolution testing for predicting bioavailability.