A certificate of analysis (COA) is the lot-specific document that shows a batch of bacteriostatic water was tested and met its specification. Reading one takes two minutes once you know what each line means, and it is the fastest way to tell a properly qualified product from an unqualified one. This guide goes line by line.
What a COA is, and what it is not
A COA is issued for a specific lot, the batch of vials filled and sealed together. It lists each test performed on that lot, the acceptance criterion, and the result. It is signed or approved by the quality unit of the manufacturer or an independent testing laboratory. A COA is not a marketing sheet, a general product specification, or a safety data sheet; those describe the product in general, whereas a COA is evidence about the vials in your hand.
Header information
- Product name and grade. Bacteriostatic water, with the preservative and its concentration stated, for example 0.9% benzyl alcohol.
- Lot (batch) number. Must match the lot printed on the vial label and the outer tray. If it does not match, the document does not describe your product.
- Manufacture date and expiration date.
- Container size and type, for example 30 mL multi-use vial.
- Date of testing and date of release.
The test lines
Description / appearance
Specification: clear, colorless solution, free from visible particulate matter. This is a visual inspection of representative vials against a black and a white background under good lighting.
Identification
Confirms that the preservative present is benzyl alcohol, usually by a chromatographic or spectroscopic method that matches the sample against a reference standard.
Benzyl alcohol assay (antimicrobial agent content)
Specification: within a defined range of the labeled 0.9% w/v (9 mg/mL). The pharmacopeial standard requires the label to state the antimicrobial agent and its proportion, and requires the content to be verified. An assay result meaningfully below the label claim means the preservative may not protect the vial through repeated entries; a result above it is a formulation error. Either is a rejection.
pH
Specification: 4.5 to 7.0, measured under defined conditions (the standard method adds a small amount of saturated potassium chloride to the sample to stabilize the electrode reading in a low-ionic-strength solution). Typical results sit around 5.5 to 6.0.
Sterility
Specification: sterile, by a pharmacopeial sterility test (membrane filtration or direct inoculation, with incubation over 14 days in two media). The result is reported as "complies" or "pass". Note that sterility applies to the sealed vial; what happens after the first puncture depends on handling and the preservative.
Bacterial endotoxins
Specification: less than 0.5 endotoxin units (EU) per mL, by the Limulus amebocyte lysate (LAL) test. Endotoxins are heat-stable components of Gram-negative bacterial cell walls that survive sterilization; a sterile product can still fail this test if the base water or the process was contaminated before sterilization. This line is the reason bacteriostatic water is made from WFI-grade water rather than ordinary purified water.
Particulate matter
Specification: within the pharmacopeial limits for sub-visible particles, tested by light obscuration or microscopic counting. Reported as counts of particles at or above 10 µm and 25 µm per container.
Absence tests inherited from the base water
Some COAs also report tests carried over from the WFI monograph: absence of calcium, sulfate and carbon dioxide, and limits on conductivity and total organic carbon. These confirm the purity of the water before the preservative was added.
Container closure integrity
Not always listed, but increasingly common: a test that the sealed vial does not leak, by dye ingress, vacuum decay or a similar method. It supports the sterility claim over shelf life.
How to check a COA in practice
- Match the lot number on the COA to the vial and the tray.
- Confirm the expiration date has not passed.
- Check that sterility, endotoxins, benzyl alcohol assay and pH are all present with a result, not just a specification.
- Look for the test methods referenced, the testing laboratory, and an approval signature or electronic release.
- File the COA with your receiving record so it can be produced if a result is ever questioned.
Red flags
- No lot number, or a "typical values" sheet presented as a COA.
- Sterility or endotoxin lines missing entirely.
- Results that exactly equal the specification on every line.
- No testing laboratory or approver identified.
- A COA dated after the product shipped to you.
Why it matters
Water is the largest component of most preparations, so its purity sets the floor for everything made from it. A COA is the only lot-specific evidence that the endotoxin, sterility and preservative requirements were actually met. Every lot BAC Water Supply ships is tested before release; COAs are available on request through our contact page. For what the specification numbers mean chemically, see what is bacteriostatic water.
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.