A buffer solution is an aqueous solution that keeps its pH value largely constant when acids or bases are added. In diagnostics and the laboratory, buffers are everywhere, as diluents, wash solutions, extraction buffers or components of test kits. As soon as they go on the market as a product, they must be manufactured reproducibly, filled with low bioburden and documented in a traceable way. This article explains what buffers do and what matters when filling them for diagnostics.
Key takeaways
- Buffers consist of a weak acid and its conjugate base, and typical examples are phosphate buffer, Tris and HEPES.
- For diagnostics, pH accuracy, low bioburden, freedom from endotoxins and exact fill volumes in small containers are what count.
- Lubeca fill fills buffers and reagents into micro screw tubes of 0.5, 1.5 and 2.0 ml as well as into bottles.
What is a buffer solution?
A buffer solution contains an acid-base pair that absorbs or releases added protons. As a result, the pH value remains stable within a range of about one unit around the pKa value. This is crucial for biological applications, because enzymes, antibodies and cells only work within a narrow pH window. A test kit whose buffer deviates from the target value delivers false results.
Which buffers are used in diagnostics?
| Buffer | pH range | Typical use |
|---|---|---|
| Phosphate-buffered saline, PBS | 7.2 to 7.4 | Dilution, washing steps, cell culture |
| Tris buffer | 7.0 to 9.0 | Molecular biology, PCR, electrophoresis |
| HEPES | 6.8 to 8.2 | Cell culture, enzyme assays |
| Citrate buffer | 3.0 to 6.2 | Antigen retrieval, preservation |
| Acetate buffer | 3.6 to 5.6 | Chromatography, protein purification |
| Extraction buffer for rapid tests | product-specific | Sample preparation in antigen rapid tests |
What matters when filling buffers?
pH value and composition
The batch must be checked with calibrated instruments and documented. Deviations of a few tenths of a pH unit can change a test result. Every batch is therefore released before filling.
Low bioburden and endotoxins
Buffers are growth media for microorganisms. They are therefore sterile filtered or preserved and filled in a controlled environment. For applications with cells or sensitive detection reactions, endotoxin limits must also be observed.
Fill volume in small containers
Extraction buffers for rapid tests are filled in volumes of a few hundred microlitres. Dosing must be accurate to the microlitre, because the ratio of sample to buffer determines the result.
Traceability
Under the In Vitro Diagnostic Regulation, all components of a test must be traceable via batch numbers. The filler documents raw materials, compounding, filling and tests for each batch.
Which containers are suitable?
- Micro screw tubes of 0.5, 1.5 and 2.0 ml for single portions in test kits
- Plastic dropper bottles for extraction buffers with metered dispensing
- Bottles from 10 to 250 ml for laboratory and wash buffers
- Bags and canisters for bulk containers in automated analysis systems
Filling of buffers at Lubeca fill
Lubeca fill was founded in 2019 and, in addition to sterile medicinal products, fills diagnostics and laboratory consumables in Çorlu near Istanbul. The equipment is designed for the smallest volumes and fills micro screw tubes with standing rim in 0.5, 1.5 and 2.0 ml as well as bottles from 10 to 250 ml. All processes are documented batch by batch. The equipment comes from Groninger, Bausch + Ströbel and Syntegon, and EU GMP certification is currently in preparation. Find out more on the page contract filling for diagnostics and laboratory consumables and in the article on contract filling of diagnostic products.
Frequently asked questions about buffer solutions
Do buffers for diagnostics have to be sterile?
Not necessarily, but low in bioburden. Many manufacturers have buffers sterile filtered to ensure shelf life and exclude contamination.
Can the filler also prepare the buffer?
Yes, if formulation and raw materials are specified. Compounding is then carried out at the filler with pH measurement and documentation.
How long do filled buffers keep?
This depends on composition, preservation and container. Shelf life is demonstrated by the manufacturer of the diagnostic through stability data.
Are you looking for a partner for the filling of buffers and reagents? Contact us.
