What Is a Certificate of Analysis (CoA)?
A certificate of analysis (CoA) is a document from a laboratory reporting the results of specific tests performed on a specific batch of a product. For supplement buyers, it is the closest thing to proof that what the label says is what the product contains.
If you have never asked a supplement company for their CoA, you have been trusting labels without independent verification that the product does not contain contaminants above acceptable limits.
We publish batch-specific CoAs for our products. It adds cost (accredited testing is not cheap), but we think transparency on this should be a standard expectation, not a premium feature reserved for the most expensive brands. We wrote a detailed guide on how to read a certificate of analysis in our purity hub, covering what to check for heavy metals, potency, detection limits, and red flags.
What a CoA Should Tell You
- Laboratory name and accreditation: Independent, accredited lab (UKAS in the UK, ISO 17025 internationally)
- Batch number: Must match the batch on your product packaging
- Heavy metals tested: Lead, cadmium, arsenic, mercury (all four, not just one or two)
- Potency results: Active ingredient levels per serving as measured by the lab
- Detection limits: "Not detected" is only meaningful if the detection limit is stated and sufficiently low
- Microbial testing: Total plate count, yeast, mould, E. coli, Salmonella for whole-food products
Why It Matters More for Algae Supplements
Algae are efficient accumulators of whatever is in their growing environment. A chlorella or phytoplankton supplement grown in contaminated water will concentrate those contaminants in the biomass. The CoA is how you verify that a specific batch of the product you bought was tested and found to be within safe limits. Without batch-specific, independently tested documentation, you are trusting the label on faith.
What our research found
When we built our own testing protocol, we reviewed CoAs from multiple algae supplement suppliers and compared them against EU regulatory requirements and industry best practice. Three patterns stood out. If you are evaluating a supplement company, these are the gaps to look for.
EU maximum heavy metal limits for food supplements are specific and binding. Under Regulation 2023/915: lead 3.0 mg/kg, cadmium 1.0 mg/kg (3.0 for seaweed-based products), mercury 0.1 mg/kg. No EU-wide arsenic maximum for supplements exists yet.
The next time a company sends you a CoA, check whether these limits are explicitly referenced or whether the document just lists a number with no benchmark beside it. The second format is nearly useless.
Heavy metals alone are not enough for algae and omega-3 products. Algae supplements should also be screened for dioxins, PCBs, and dioxin-like PCBs. Omega-3 products need peroxide value, anisidine value, and TOTOX to confirm the oil has not oxidised.
A CoA that tests only heavy metals and microbiology is still better than no independent testing; most products on the market do not reach even that level. But it is doing the minimum, not a thorough job.
When we set up accredited testing for our own batches, the cost surprised us. A full panel through a UKAS-accredited lab runs from £200 to £800 per batch depending on the analyte list. We test every batch (heavy metals, microbiology, dioxins, and PCBs for our phytoplankton) and that cost is built into the price.
Companies that offer algae supplements at very low price points are usually not running this full panel per batch. The economics do not allow it.
Sources
Cara Hayes, MSc Nutrition and Dietetics (University of Sydney), writes all content in the Phytality Knowledge Centre. Read our editorial policy.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your healthcare provider before starting any supplement.
Methodology and Disclosure
Phytality tests every batch through independent laboratories and publishes CoAs. We have a commercial interest in testing transparency being valued. Testing standards (UKAS, ISO 17025) are internationally recognised accreditation frameworks. EU regulatory limits for heavy metals are from Commission Regulation (EU) 2023/915 (which replaced EC No 1881/2006).
Last reviewed: March 2026
