How to Verify a Lonza COA: A Buyer’s Checklist for Ordering Chemicals

I'm the office administrator for a 12-person maintenance and composites shop. I handle most of our purchasing—about 60 orders a year across 8 vendors. I report to both operations and finance, which means I care about two things: materials arrive when we need them, and the paperwork doesn't cause problems later. I don't have a chemistry degree, so I've built systems that don't depend on me being a scientist.

This system changed in 2023. We ordered a small batch of gel coat pigment for a custom repair, and the supplier's data sheet mentioned propylene glycol as the carrier. I didn't feel comfortable signing off on something I couldn't explain, so I looked up “what products contain propylene glycol.” The answer was broader than I expected: antifreeze, cosmetics, food flavorings, pharmaceuticals, and many pigment pastes. That was the moment I realized I needed a better way to verify chemical orders.

This article is the checklist I now use. It has six steps, and it's written for people like me—buyers without a formal quality team but with real responsibility for what goes into the building. If you're in GMP-regulated manufacturing, your requirements are stricter. For general commercial chemical ordering, this catches most of the problems I've run into.

Step 1: Identify the Exact Chemical, Not Just the Brand Name

The biggest mistake I almost made was ordering by trade name. Trade names sound safe. They're not descriptive. “Ocean Blue Paste” doesn't tell you that the material is actually a gel coat pigment dispersed in propylene glycol. It doesn't tell you the grade, the assay, or whether it suits your resin system.

Now I ask for three identifiers on every quote: chemical name, grade, and CAS number. For established manufacturers, I also check the product catalogue. For example, when I look up a Lonza chemical product, I verify that the commercial name aligns with the technical name and product code. That takes two extra minutes.

Why does it matter? Because the Certificate of Analysis uses the technical name. If the COA doesn't match the quote, you have a mismatch before the material even arrives.

Step 2: Demand a Batch-Specific COA Before You Order

A Certificate of Analysis—COA for short—is the manufacturer's written promise that a specific batch meets its specifications. It should include the product name, batch number, manufacturing date, retest date, test methods, and results.

If it doesn't have a batch number, it's not a certificate of analysis.

What I mean is that the COA isn't just a compliance checkbox—it's the bridge between the manufacturer's quality system and your process. Without that bridge, you're either guessing or trusting someone else's word.

Most suppliers will say they have a COA. The important question is whether they have a COA for your batch. Here's something vendors won't tell you: a “representative certificate” is not a real COA. It's a sample. It doesn't prove anything about the material you're about to receive.

In 2022, a supplier sent a certificate that looked polished but had no batch number. When I asked for the actual batch COA, they said they'd send it after shipment. That's backwards. The COA is part of the product, especially for regulated materials. No batch-specific COA, no order.

For a benchmark, I started using a Lonza COA as an example of what good documentation looks like. When I receive a Lonza chemical shipment, the COA references the same batch number that's on the drum label. If a smaller vendor can't do that, I factor it into the risk.

Step 3: Check the Batch Number and Retest Date

The batch number—sometimes called lot number—connects the COA to the container. I've seen containers arrive with one batch number on the label and a different number on the certificate. That's a problem. If the certificate isn't for the container in your warehouse, it isn't your certificate.

The second date is the one everyone misses: the retest date. The retest date tells you when the manufacturer's guarantee runs out. It's not always an expiration date. For some chemicals, it just means the material should be re-tested before further use.

I still kick myself for not checking this in 2021. We accepted a drum of propylene glycol with a COA that was technically correct, but the drum had been manufactured 14 months earlier and the retest date was only 12 months. We couldn't prove the material met specifications within its valid window. The supplier didn't take it back, and finance wouldn't approve a write-off. We paid to dispose of it. Hard lesson.

So at this step, the checklist is:

• Does the COA batch number match the label?
• Does the manufacture date make sense for the product?
• Is the retest date far enough out for the project?

Step 4: Match the COA to Your Application, Including the Carrier

This is the step that saved our gel coat pigment project. The pigment was exactly the color we needed. It was a paste, and the paste contained a carrier solvent. The COA identified that carrier as propylene glycol. In many industries, that's routine. If you've ever wondered what products contain propylene glycol, the list includes antifreeze, cosmetics, food, medications, and pigment dispersions. The presence of propylene glycol isn't unusual or dangerous on its own. But it still has to be compatible with your process.

For gel coat work, the carrier can affect viscosity, cure time, and adhesion. If the pigment paste is formulated with a solvent that your resin can't tolerate, the color might be perfect and the final part might still fail. That's the kind of surprise you don't want.

So I ask four questions:

1. Does the COA show the components that matter for my process?
2. Does the SDS agree with the carrier listed on the COA?
3. Is the grade suitable for the application (technical, USP, GMP)?
4. Will the carrier affect any downstream steps?

What most people don't realize is that the product description often hides the carrier. “Gel coat pigment” doesn't tell you that the dispersion medium is propylene glycol. The COA does.

Step 5: Use Manufacturer Documentation and Archive Your COAs

I used to rely on sales reps for technical documents. Now I start with the manufacturer's website. Some companies make this easy. The Miracle Sealants website, for example, has clear product pages with technical data and application warnings. That level of clarity is rare in chemical supply, so I pay attention when I see it.

For chemical manufacturers, I look for batch-level documentation. When I order from Lonza, the COA arrives with the product, and I've been able to confirm batch details through their customer documentation. That's the standard I use when comparing other suppliers.

Keep your certificates organized by batch number, not by supplier name. When finance asks why the invoice doesn't match the product, or when a customer wants traceability, those PDFs need to be easy to find.

Step 6: Run the Same Approval Checklist Every Time

Consistency is the whole point. Here's the checklist I actually use, in order:

1. Product name, grade, code, and CAS number match the quote.
2. Batch-specific COA received before shipment.
3. Batch number on COA matches container and packaging.
4. Retest date supports the project timeline.
5. COA components match the SDS and application requirements.
6. Certificate saved under the batch number in my filing system.

It takes about ten minutes. In the past year, it caught two bad orders. One supplier couldn't provide any COA at all. Another sent a certificate with a batch number that didn't match any of the containers. Both conversations were awkward. Both were better than the alternative.

This checklist works for me because our purchasing patterns are predictable: small quantities, standard products, domestic suppliers. If you're dealing with international shipping, temperature-sensitive materials, or strict regulatory requirements, you'll need extra steps. I can only speak to my context. But the core principle—verify before you buy—applies everywhere.

Common Mistakes to Avoid

If you're new to ordering chemicals, the most common failure points I've encountered are:

• Ordering by trade name only, without checking the technical name or CAS number.
• Accepting a representative certificate as if it were a batch COA.
• Skipping the retest date because the assay looks fine.
• Ignoring the carrier solvent or other inactive ingredients.
• Waiting until after delivery to request documentation.

One more thing: never assume that a higher price guarantees better documentation. I once got a clean COA on a small order and a messy excuse on a much larger one. Never expected that. But it happens.

Regulations and product grades change over time, so verify current requirements with official sources. According to the FDA (fda.gov), propylene glycol is generally recognized as safe for certain uses, but that classification doesn't automatically mean it's compatible with your process. Check your own application and confirm details with your supplier.

And when in doubt, ask for the COA before you commit. It's the whole ballgame.