Author: Offline Receipts Team

  • HPLC vs Mass Spectrometry: What Each Lab Test Actually Proves

    Two tests show up on almost every serious certificate of analysis: HPLC and mass spectrometry. They are often listed side by side, so people assume they do the same job. They do not. One tells you how pure a sample is. The other tells you what the sample actually is. A report that has only one of them is missing half the proof.

    HPLC: the purity test

    High performance liquid chromatography pushes a dissolved sample through a packed column under pressure. Different components travel through the column at different speeds, so they exit at different times. A detector records each one as it comes out, producing a chart of peaks called a chromatogram.

    The largest peak should be the target compound. Its share of the total peak area is reported as purity, for example 99.1 percent. The smaller peaks are impurities, such as fragments or byproducts from manufacturing.

    What HPLC cannot tell you

    • Identity. A clean single peak proves the sample is mostly one thing. It does not prove that one thing is the compound on the label.
    • Hidden impurities. Two substances can exit the column at nearly the same time and appear as one peak.
    • Anything the detector cannot see. Detectors look at a set wavelength, so some substances barely register.

    Mass spectrometry: the identity test

    Mass spectrometry, or MS, turns molecules into charged particles and measures their mass to charge ratio. From that, the instrument works out molecular weight. The report compares the observed weight with the expected weight calculated from the compound’s known structure. A close match is strong evidence the molecule is what it claims to be.

    What mass spectrometry cannot tell you

    • Purity. MS confirms the target is present. It is not designed to report what percentage of the sample it makes up.
    • Quantity. It does not tell you how many milligrams are in the vial.

    Why you need both

    Put the two together and the gaps close. HPLC says the sample is, for example, 99 percent one substance. MS says that substance has the correct molecular weight. Many labs run them as one combined method, written as LC/MS, which separates the sample and identifies each peak in a single run.

    HPLCMass spec
    Question it answersHow pure is the sample?Is it the right molecule?
    What it measuresSeparation of components over timeMass of the molecules
    Typical resultPurity as area percent, plus a chromatogramObserved vs expected molecular weight
    Blind spotCannot confirm identity by itselfDoes not measure purity well

    Other tests you may see on a report

    • Net content or quantity. Confirms how much compound is actually in the vial.
    • Endotoxin testing. Often run with the LAL method described in USP <85>, it checks for bacterial endotoxins.
    • Sterility. Checks for microbial growth.
    • Heavy metals and residual solvents. Screens for contaminants left over from manufacturing.

    Three questions to ask any supplier

    • Does the COA include both a purity result and an identity result?
    • Is the chromatogram shown, or only a number?
    • Does the batch number on the COA match the batch you will receive?

    If the answer to any of these is no, ask why. A supplier with nothing to hide will show you the receipts.

    Want to see both tests on one report? Offline Peptides publishes an independent COA for every batch it sells. See the COAs

    Sources

    For educational purposes only. Compounds discussed on this site are for laboratory research use only and are not for human or animal use. Nothing here is medical advice.

  • How to Read a Certificate of Analysis (COA): A Line by Line Guide

    A certificate of analysis, or COA, is the receipt for a research compound. It is the document that says an independent lab tested a specific batch and found it to be what the label claims. A good one answers three questions: is it the right compound, how pure is it, and how much is in the vial. A bad one answers none of them while looking official.

    This guide walks through a COA line by line, so you can tell the difference in under two minutes.

    What a COA actually is

    A COA is a lab report tied to one batch. It is not a product description and it is not a marketing sheet. Because it covers one batch only, a COA from last year, or from a different batch, tells you nothing about the vial in front of you.

    Most COAs have four parts: the header, an identity result, a purity result, and a quantity result. Here is what to look for in each.

    1. The header: who tested it, and when

    The top of the report should name the testing lab, give a report date, and list a sample or batch number. Check each one:

    • Lab name and contact details. A real lab can be looked up. If the report has no lab name, or only a logo, treat it as unverified.
    • Accreditation. Many labs hold ISO/IEC 17025 accreditation, the international standard for testing laboratory competence. It is a strong signal, though not every good lab lists it.
    • Report date. It should be recent enough to match the batch being sold.
    • Batch number. This is the link between the paper and the product. If it does not match the batch you have, the COA is not your receipt.

    2. Identity: is it the right compound?

    Identity is usually confirmed with mass spectrometry, often shortened to MS. The instrument measures the mass of the molecules in the sample. The report compares the expected molecular weight, calculated from the compound’s known structure, with the observed molecular weight the instrument found.

    What you want to see: the observed value sits very close to the expected value, usually within a fraction of a dalton for small molecules and within the instrument’s stated tolerance for larger ones. A report that lists a purity number but no identity result has skipped the most basic question.

    3. Purity: how much of the sample is the target?

    Purity is usually measured with high performance liquid chromatography, or HPLC. The sample is pushed through a column that separates its components, and a detector records each one as a peak on a chart called a chromatogram.

    • The main peak is the target compound. Its share of the total peak area is the purity figure, often written as area percent.
    • Smaller peaks are impurities or related substances. A few small peaks are normal.
    • The chromatogram itself should be shown. A purity number with no chart behind it is a claim, not a result.

    Research grade material commonly reports purity at or above 98 percent. Treat a flat 100 percent with suspicion: real instruments almost always detect something.

    4. Quantity: is the amount in the vial right?

    A vial labeled 10 mg should contain about 10 mg of the target compound. Some COAs report this as net content or quantity, measured against a reference standard. Purity and quantity are different: a sample can be 99 percent pure and still be underfilled. If a supplier only reports purity, you only know half the story.

    5. Matching the COA to your vial

    The final check connects the paper to the product. Look for the batch number, and on some reports a photo of the tested vial, including the cap color and label. If the photo, batch or label does not match what you have, ask the supplier before using the material in any research.

    Five red flags

    1. No lab name, or a lab you cannot find anywhere.
    2. A purity figure with no chromatogram and no identity result.
    3. A perfect 100 percent purity score.
    4. A batch number or date that does not match the product.
    5. Signs of editing: mismatched fonts, blurred numbers, or a lab that will not confirm the report when you ask.

    The bottom line

    A COA is only as good as the three answers it gives: identity, purity and quantity, all tied to one batch. If any of the three is missing, you do not have a receipt. You have a flyer.

    Want to see real receipts? Offline Peptides publishes an independent COA for every batch it sells. See the COAs

    Sources

    For educational purposes only. Compounds discussed on this site are for laboratory research use only and are not for human or animal use. Nothing here is medical advice.