What Is HPLC Testing? How It Verifies Pharmaceutical Purity
How HPLC Works
HPLC works by pushing a liquid sample through a column packed with a stationary phase material under high pressure. Different compounds in the sample interact differently with the stationary phase — some pass through quickly, others slowly. This separation produces a chromatogram: a graph showing peaks at different retention times, where each peak represents a specific compound.
The area under each peak is proportional to the concentration of that compound. By comparing peak areas to a known reference standard, analysts can calculate the exact percentage of each compound in the sample.
What HPLC Tests in Bacteriostatic Water
For bacteriostatic water, HPLC is used to verify:
- Benzyl alcohol concentration: Must be 0.9% ± 0.05% per USP specification
- Absence of degradation products: Benzyl alcohol degrades to benzaldehyde and benzoic acid — HPLC detects and quantifies these
- Absence of unexpected impurities: Any unknown peak in the chromatogram flags a potential contamination issue
Reading an HPLC Result on a COA
On a Renew Lab Group Certificate of Analysis, the HPLC section shows:
| Test | Specification | Result |
|---|---|---|
| Benzyl Alcohol Assay | 0.85% – 0.95% | Lot-specific value (e.g., 0.91%) |
| Related Substances | NMT 0.1% any individual | Complies |
Why Not All Bacteriostatic Water Is Equal
Without HPLC testing, there is no reliable way to verify benzyl alcohol concentration. Products sold without COA documentation may have incorrect preservative levels — too low means inadequate antimicrobial protection; too high raises cytotoxicity concerns. Renew Lab Group performs HPLC testing on every production lot and provides the results with every shipment.
Related: How HPLC Testing Ensures Purity | Certificate of Analysis | Our Lab Services
